Genomic analyses of flowering transition and inflorescence development in grapevine = Análisis genómicos de la transición floral y del desarrollo de la inflorescencia en la vid

The general objective of this work is to analyze the regulatory processes underlying flowering transition and inflorescence and flower development in grapevine. Most of these crucial developmental events take place within buds growing during two seasons in two consecutive years. During the first season, the shoot apical meristem within the bud differentiates all the basic elements of the shoot including flowering transition in lateral primordia and development of inflorescence primordia. These events practically end with bud dormancy. The second season, buds resume shoot growth associated to flower formation and development. In grapevine, the lateral meristems can give rise either to tendril or inflorescence primordia that are homologous organs. With this purpose, we performed global transcriptome analyses along the bud annual cycle and during inflorescence and tendril development. In addition, we approach the genomic analysis of the MIKC type MADS-box gene family in grapevine to identify all its members and assign them putative biological functions. Regarding buds developmental cycle, the results indicate that the main factors explaining the global gene expression differences were the processes of bud dormancy and active growth as well as stress responses. Non dormant buds exhibited up-regulation in functional categories typical of actively proliferating and growing cells (photosynthesis, cell cycle regulation, chromatin assembly) whereas in dormant ones the main functional categories up-regulated were associated to stress response pathways together with transcripts related to starch catabolism. Major transcriptional changes during the dormancy period were associated to the para/endodormancy, endo/ecodormancy and ecodormancy/bud break transitions. Global transcriptional analyses along tendril and inflorescence development suggested that these two homologous organs share a common transcriptional program related to cell proliferation functions. Both structures showed a progressive decrease in the expression of categories such as cell-cycle, auxin metabolism/signaling, DNA metabolism, chromatin assembly and a cluster of five transcripts belonging to the GROWTH-REGULATING FACTOR (GRF) transcription factor family, that are known to control cell proliferation in other species and determine the size of lateral organs. However, they also showed organ specific transcriptional programs that can be related to their differential organ structure and function. Tendrils showed higher transcription of genes related to photosynthesis, hormone signaling and secondary metabolism than inflorescences, while inflorescences have higher transcriptional activity for genes encoding transcription factors (especially those belonging to the MADS-box gene family). Further analysis along inflorescence development evidenced the relevance of additional functions likely related to processes of flower development such as fatty acid and lipid metabolism, jasmonate signaling and oxylipin biosynthesis. The transcriptional analyses performed highlighted the relevance of several groups of transcriptional regulators in the developmental processes studied. The expression profiles along bud development revealed significant differences for some MADS-box subfamilies in relation to other plant species, like the members of the FLC and SVP subfamilies suggesting new roles for these groups in grapevine. In this way, it was found that VvFLC2 and VvAGL15.1 could participate, together with some members of the SPL-L family, in dormancy regulation, as was shown for some of them in other woody plants. Similarly, the expression patterns of the VvFLC1, VvFUL, VvSOC1.1 (together with VvFT, VvMFT1 and VFL) genes could indicate that they play a role in flowering transition in grapevine, in parallel to their roles in other plant systems. The expression levels of VFL, the grapevine LEAFY homolog, could be crucial to specify the development of inflorescence and flower meristems instead of tendril meristems. MADS-box genes VvAP3.1 and 2, VvPI, VvAG1 and 3, VvSEP1-4, as well as VvBS1 and 2 are likely associated with the events of flower meristems and flower organs differentiation, while VvAP1 and VvFUL-L (together with VvSOC1.1, VvAGL6.2) could be involved on tendril development given their expression patterns. In addition, the biological function ofVvAP1 and VvTFL1A was analyzed using a gene silencing approach in transgenic grapevine plants. Our preliminary results suggested a possible role for both genes in the initiation and differentiation of tendrils. Finally, the genomic analysis of the MADS-box gene family in grapevine revealed differential features regarding number and expression pattern of genes putatively involved in the flowering transition process as compared to those involved in the specification of flower and fruit organ identity. Altogether, the results obtained allow identifying putative candidate genes and pathways regulating grapevine reproductive developmental processes paving the way to future experiments demonstrating specific gene biological functions. RESUMEN El objetivo general de este trabajo es analizar los procesos regulatorios subyacentes a la inducción floral así como al desarrollo de la inflorescencia y la flor en la vid. La mayor parte de estos eventos cruciales tienen lugar en las yemas a lo largo de dos estaciones de crecimiento consecutivas. Durante la primera estación, el meristemo apical contenido en la yema diferencia los elementos básicos del pámpano, lo cual incluye la inducción de la floración en los meristemos laterales y el subsiguiente desarrollo de primordios de inflorescencia. Estos procesos prácticamente cesan con la entrada en dormición de la yema. En la segunda estación, se reanuda el crecimiento del pámpano acompañado por la formación y desarrollo de las flores. En la vid, los meristemos laterales pueden dar lugar a primordios de inflorescencia o de zarcillo que son considerados órganos homólogos. Con este objetivo llevamos a cabo un estudio a nivel del transcriptoma de la yema a lo largo de su ciclo anual, así como a lo largo del desarrollo de la inflorescencia y del zarcillo. Además realizamos un análisis genómico de la familia MADS de factores transcripcionales (concretamente aquellos del tipo MIKC) para identificar todos sus miembros y tratar de asignarles posibles funciones biológicas. En cuanto al ciclo de desarrollo de la yema, los resultados indican que los principales factores que explican las diferencias globales en la expresión génica fueron los procesos de dormición de la yema y el crecimiento activo junto con las respuestas a diversos tipos de estrés. Las yemas no durmientes mostraron un incremento en la expresión de genes contenidos en categorías funcionales típicas de células en proliferación y crecimiento activo (como fotosíntesis, regulación del ciclo celular, ensamblaje de cromatina), mientras que en las yemas durmientes, las principales categorías funcionales activadas estaban asociadas a respuestas a estrés, así como con el catabolismo de almidón. Los mayores cambios observados a nivel de transcriptoma en la yema coincidieron con las transiciones de para/endodormición, endo/ecodormición y ecodormición/brotación. Los análisis transcripcionales globales a lo largo del desarrollo del zarcillo y de la inflorescencia sugirieron que estos dos órganos homólogos comparten un programa transcripcional común, relacionado con funciones de proliferación celular. Ambas estructuras mostraron un descenso progresivo en la expresión de genes pertenecientes a categorías funcionales como regulación del ciclo celular, metabolismo/señalización por auxinas, metabolismo de ADN, ensamblaje de cromatina y un grupo de cinco tránscritos pertenecientes a la familia de factores transcripcionales GROWTH-REGULATING FACTOR (GRF), que han sido asociados con el control de la proliferación celular y en determinar el tamaño de los órganos laterales en otras especies. Sin embargo, también pusieron de manifiesto programas transcripcionales que podrían estar relacionados con la diferente estructura y función de dichos órganos. Los zarcillos mostraron mayor actividad transcripcional de genes relacionados con fotosíntesis, señalización hormonal y metabolismo secundario que las inflorescencias, mientras que éstas presentaron mayor actividad transcripcional de genes codificantes de factores de transcripción (especialmente los pertenecientes a la familia MADS-box). Análisis adicionales a lo largo del desarrollo de la inflorescencia evidenciaron la relevancia de otras funciones posiblemente relacionadas con el desarrollo floral, como el metabolismo de lípidos y ácidos grasos, la señalización mediada por jasmonato y la biosíntesis de oxilipinas. Los análisis transcripcionales llevados a cabo pusieron de manifiesto la relevancia de varios grupos de factores transcripcionales en los procesos estudiados. Los perfiles de expresión estudiados a lo largo del desarrollo de la yema mostraron diferencias significativas en algunas de las subfamilias de genes MADS con respecto a otras especies vegetales, como las observadas en los miembros de las subfamilias FLC y SVP, lo cual sugiere que podrían desempeñar nuevas funciones en la vid. En este sentido, se encontró que los genes VvFLC2 y VvAGL15.1 podrían participar, junto con algunos miembros de la familia SPL-L, en la regulación de la dormición. De un modo similar, los patrones de expresión de los genes VvFLC1, VvFUL, VvSOC1.1 (junto con VvFT, VvMFT1 y VFL) podría indicar que desempeñan un papel en la regulación de la inducción de la floración en la vid, como se ha observado en otros sistemas vegetales. Los niveles de expresión de VFL, el homólogo en vid del gen LEAFY de A. thaliana podrían ser cruciales para la especificación del desarrollo de meristemos de inflorescencia y flor en lugar de meristemos de zarcillo. Los genes VvAP3.1 y 2, VvPI, VvAG1 y 3, VvSEP1-4, así como VvBS1 y 2 parecen estar asociados con los eventos de diferenciación de meristemos y órganos florales, mientras que VvAP1 y VvFUL-L (junto con VvSOC1.1 y VvAGL6.2) podrían estar implicados en el desarrollo del zarcillo dados sus patrones de expresión. Adicionalmente, se analizó la función biológica de los genes VvAP1 y VvTFL1A por medio de una estrategia de silenciamiento génico. Los datos preliminares sugieren un posible papel para ambos genes en la iniciación y diferenciación de los zarcillos. Finalmente, el análisis genómico de la familia MADS en vid evidenció diferencias con respecto a otras especies vegetales en cuanto a número de miembros y patrón de expresión en genes supuestamente implicados en la inducción de la floración, en comparación con aquellos relacionados con la especificación de identidad de órganos florales y desarrollo del fruto. En conjunto, los resultados obtenidos han permitido identificar posibles rutas y genes candidatos a participar en la regulación de los procesos de desarrollo reproductivo de la vid, sentando las bases de futuros experimentos encaminados a conocer la funciones biológicas de genes específicos.

The role of BoFLC2 in cauliflower (Brassica oleracea var. botrytis L.) reproductive development

In agricultural species that are sexually propagated or whose marketable organ is a reproductive structure, management of the flowering process is critical. Inflorescence development in cauliflower is particularly complex, presenting unique challenges for those seeking to predict and manage flowering time. In this study, an integrated physiological and molecular approach was used to clarify the environmental control of cauliflower reproductive development at the molecular level. A functional allele of BoFLC2 was identified for the first time in an annual brassica, along with an allele disrupted by a frameshift mutation (boflc2). In a segregating F2 population derived from a cross between late-flowering (BoFLC2) and early-flowering (boflc2) lines, this gene behaved in a dosage-dependent manner and accounted for up to 65% of flowering time variation. Transcription of BoFLC genes was reduced by vernalization, with the floral integrator BoFT responding inversely. Overall expression of BoFT was significantly higher in early-flowering boflc2 lines, supporting the idea that BoFLC2 plays a key role in maintaining the vegetative state. A homologue of Arabidopsis VIN3 was isolated for the first time in a brassica crop species and was up-regulated by two days of vernalization, in contrast to findings in Arabidopsis where prolonged exposure to cold was required to elicit up-regulation. The correlations observed between gene expression and flowering time in controlled-environment experiments were validated with gene expression analyses of cauliflowers grown outdoors under 'natural' vernalizing conditions, indicating potential for transcript levels of flowering genes to form the basis of predictive assays for curd initiation and flowering time.

Ensemble projections for wine production in the Douro Valley of Portugal

Wine production is largely governed by atmospheric conditions, such as air temperature and precipitation, together with soil management and viticultural/enological practices. Therefore, anthropogenic climate change is likely to have important impacts on the winemaking sector worldwide. An important winemaking region is the Portuguese Douro Valley, which is known by its world-famous Port Wine. The identification of robust relationships between atmospheric factors and wine parameters is of great relevance for the region. A multivariate linear regression analysis of a long wine production series (1932–2010) reveals that high rainfall and cool temperatures during budburst, shoot and inflorescence development (February-March) and warm temperatures during flowering and berry development (May) are generally favourable to high production. The probabilities of occurrence of three production categories (low, normal and high) are also modelled using multinomial logistic regression. Results show that both statistical models are valuable tools for predicting the production in a given year with a lead time of 3–4 months prior to harvest. These statistical models are applied to an ensemble of 16 regional climate model experiments following the SRES A1B scenario to estimate possible future changes. Wine production is projected to increase by about 10 % by the end of the 21st century, while the occurrence of high production years is expected to increase from 25 % to over 60 %. Nevertheless, further model development will be needed to include other aspects that may shape production in the future. In particular, the rising heat stress and/or changes in ripening conditions could limit the projected production increase in future decades.

Statistical modelling of grapevine yield in the Port Wine region under present and future climate conditions

The impact of projected climate change on wine production was analysed for the Demarcated Region of Douro, Portugal. A statistical grapevine yield model (GYM) was developed using climate parameters as predictors. Statistically significant correlations were identified between annual yield and monthly mean temperatures and monthly precipitation totals during the growing cycle. These atmospheric factors control grapevine yield in the region, with the GYM explaining 50.4% of the total variance in the yield time series in recent decades. Anomalously high March rainfall (during budburst, shoot and inflorescence development) favours yield, as well as anomalously high temperatures and low precipitation amounts in May and June (May: flowering and June: berry development). The GYM was applied to a regional climate model output, which was shown to realistically reproduce the GYM predictors. Finally, using ensemble simulations under the A1B emission scenario, projections for GYM-derived yield in the Douro Region, and for the whole of the twenty-first century, were analysed. A slight upward trend in yield is projected to occur until about 2050, followed by a steep and continuous increase until the end of the twenty-first century, when yield is projected to be about 800 kg/ha above current values. While this estimate is based on meteorological parameters alone, changes due to elevated CO2 may further enhance this effect. In spite of the associated uncertainties, it can be stated that projected climate change may significantly benefit wine yield in the Douro Valley.

Silencing of the ACC synthase gene ACACS2 causes delayed flowering in pineapple [Ananas comosus (L.) Merr.]

Flowering is a crucial developmental stage in the plant life cycle. A number of different factors, from environmental to chemical, can trigger flowering. In pineapple, and other bromeliads, it has been proposed that flowering is triggered by a small burst of ethylene production in the meristem in response to environmental cues. A 1-amino-cyclopropane-1-carboxylate synthase (ACC synthase) gene has been cloned from pineapple (ACACS2), which is induced in the meristem under the same environmental conditions that induce flowering. Two transgenic pineapple lines have been produced containing co-suppression constructs designed to down-regulate the expression of the ACACS2 gene. Northern analysis revealed that the ACACS2 gene was silenced in a number of transgenic plants in both lines. Southern hybridization revealed clear differences in the methylation status of silenced versus non-silenced plants by the inability of a methylation-sensitive enzyme to digest within the ACACS2 DNA extracted from silenced plants, indicating that methylation is the cause of the observed co-suppression of the ACACS2 gene. Flowering characteristics of the transgenic plants were studied under field conditions in South East Queensland, Australia. Flowering dynamics studies revealed significant differences in flowering behaviour, with transgenic plants exhibiting silencing showing a marked delay in flowering when compared with non-silenced transgenic plants and control non-transformed plants. It is argued that the ACACS2 gene is one of the key contributors towards triggering 'natural flowering' in mature pineapples under commercial field conditions.

Inflorescence and floral development of Dahlstedtia species (Leguminosae: Papilionoideae: Millettieae)

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Overexpression of the kiwifruit SVP3 gene affects reproductive development and suppresses anthocyanin biosynthesis in petals, but has no effect on vegetative growth, dormancy, or flowering time

SVP-like MADS domain transcription factors have been shown to regulate flowering time and both inflorescence and flower development in annual plants, while having effects on growth cessation and terminal bud formation in perennial species. Previously, four SVP genes were described in woody perennial vine kiwifruit (Actinidia spp.), with possible distinct roles in bud dormancy and flowering. Kiwifruit SVP3 transcript was confined to vegetative tissues and acted as a repressor of flowering as it was able to rescue the Arabidopsis svp41 mutant. To characterize kiwifruit SVP3 further, ectopic expression in kiwifruit species was performed. Ectopic expression of SVP3 in A. deliciosa did not affect general plant growth or the duration of endodormancy. Ectopic expression of SVP3 in A. eriantha also resulted in plants with normal vegetative growth, bud break, and flowering time. However, significantly prolonged and abnormal flower, fruit, and seed development were observed, arising from SVP3 interactions with kiwifruit floral homeotic MADS-domain proteins. Petal pigmentation was reduced as a result of SVP3-mediated interference with transcription of the kiwifruit flower tissue-specific R2R3 MYB regulator, MYB110a, and the gene encoding the key anthocyanin biosynthetic step, F3GT1. Constitutive expression of SVP3 had a similar impact on reproductive development in transgenic tobacco. The flowering time was not affected in day-neutral and photoperiod-responsive Nicotiana tabacum cultivars, but anthesis and seed germination were significantly delayed. The accumulation of anthocyanin in petals was reduced and the same underlying mechanism of R2R3 MYB NtAN2 transcript reduction was demonstrated.

The Gerbera cDNA Microarray: A Tool for Large-Scale Identification of Genes Involved in Flower Development

During the past ten years, large-scale transcript analysis using microarrays has become a powerful tool to identify and predict functions for new genes. It allows simultaneous monitoring of the expression of thousands of genes and has become a routinely used tool in laboratories worldwide. Microarray analysis will, together with other functional genomics tools, take us closer to understanding the functions of all genes in genomes of living organisms. Flower development is a genetically regulated process which has mostly been studied in the traditional model species Arabidopsis thaliana, Antirrhinum majus and Petunia hybrida. The molecular mechanisms behind flower development in them are partly applicable in other plant systems. However, not all biological phenomena can be approached with just a few model systems. In order to understand and apply the knowledge to ecologically and economically important plants, other species also need to be studied. Sequencing of 17 000 ESTs from nine different cDNA libraries of the ornamental plant Gerbera hybrida made it possible to construct a cDNA microarray with 9000 probes. The probes of the microarray represent all different ESTs in the database. From the gerbera ESTs 20% were unique to gerbera while 373 were specific to the Asteraceae family of flowering plants. Gerbera has composite inflorescences with three different types of flowers that vary from each other morphologically. The marginal ray flowers are large, often pigmented and female, while the central disc flowers are smaller and more radially symmetrical perfect flowers. Intermediate trans flowers are similar to ray flowers but smaller in size. This feature together with the molecular tools applied to gerbera, make gerbera a unique system in comparison to the common model plants with only a single kind of flowers in their inflorescence. In the first part of this thesis, conditions for gerbera microarray analysis were optimised including experimental design, sample preparation and hybridization, as well as data analysis and verification. Moreover, in the first study, the flower and flower organ-specific genes were identified. After the reliability and reproducibility of the method were confirmed, the microarrays were utilized to investigate transcriptional differences between ray and disc flowers. This study revealed novel information about the morphological development as well as the transcriptional regulation of early stages of development in various flower types of gerbera. The most interesting finding was differential expression of MADS-box genes, suggesting the existence of flower type-specific regulatory complexes in the specification of different types of flowers. The gerbera microarray was further used to profile changes in expression during petal development. Gerbera ray flower petals are large, which makes them an ideal model to study organogenesis. Six different stages were compared and specifically analysed. Expression profiles of genes related to cell structure and growth implied that during stage two, cells divide, a process which is marked by expression of histones, cyclins and tubulins. Stage 4 was found to be a transition stage between cell division and expansion and by stage 6 cells had stopped division and instead underwent expansion. Interestingly, at the last analysed stage, stage 9, when cells did not grow any more, the highest number of upregulated genes was detected. The gerbera microarray is a fully-functioning tool for large-scale studies of flower development and correlation with real-time RT-PCR results show that it is also highly sensitive and reliable. Gene expression data presented here will be a source for gene expression mining or marker gene discovery in the future studies that will be performed in the Gerbera Laboratory. The publicly available data will also serve the plant research community world-wide.

The role of MADS and TCP transcription factors in Gerbera hybrida flower development

Angiosperms represent a huge diversity in floral structures. Thus, they provide an attractive target for comparative developmental genetics studies. Research on flower development has focused on few main model plants, and studies on these species have revealed the importance of transcription factors, such as MADS-box and TCP genes, for regulating the floral form. The MADS-box genes determine floral organ identities, whereas the TCP genes are known to regulate flower shape and the number of floral organs. In this study, I have concentrated on these two gene families and their role in regulating flower development in Gerbera hybrida, a species belonging to the large sunflower family (Asteraceae). The Gerbera inflorescence is comprised of hundreds of tightly clustered flowers that differ in their size, shape and function according to their position in the inflorescence. The presence of distinct flower types tells Gerbera apart from the common model species that bear only single kinds of flowers in their inflorescences. The marginally located ray flowers have large bilaterally symmetrical petals and non-functional stamens. The centrally located disc flowers are smaller, have less pronounced bilateral symmetry and carry functional stamens. Early stages of flower development were studied in Gerbera to understand the differentiation of flower types better. After morphological analysis, we compared gene expression between ray and disc flowers to reveal transcriptional differences in flower types. Interestingly, MADS-box genes showed differential expression, suggesting that they might take part in defining flower types by forming flower-type-specific regulatory complexes. Functional analysis of a CYCLOIDEA-like TCP gene GhCYC2 provided evidence that TCP transcription factors are involved in flower type differentiation in Gerbera. The expression of GhCYC2 is ray-flower-specific at early stages of development and activated only later in disc flowers. Overexpression of GhCYC2 in transgenic Gerbera-lines causes disc flowers to obtain ray-flower-like characters, such as elongated petals and disrupted stamen development. The expression pattern and transgenic phenotypes further suggest that GhCYC2 may shape ray flowers by promoting organ fusion. Cooperation of GhCYC2 with other Gerbera CYC-like TCP genes is most likely needed for proper flower type specification, and by this means for shaping the elaborate inflorescence structure. Gerbera flower development was also approached by characterizing B class MADS-box genes, which in the main model plants are known regulators of petal and stamen identity. The four Gerbera B class genes were phylogenetically grouped into three clades; GGLO1 into the PI/GLO clade, GDEF2 and GDEF3 into the euAP3 clade and GDEF1 into the TM6 clade. Putative orthologs for GDEF2 and GDEF3 were identified in other Asteraceae species, which suggests that they appeared through an Asteraceae-specific duplication. Functional analyses indicated that GGLO1 and GDEF2 perform conventional B-function as they determine petal and stamen identities. Our studies on GDEF1 represent the first functional analysis of a TM6-like gene outside the Solanaceae lineage and provide further evidence for the role of TM6 clade members in specifying stamen development. Overall, the Gerbera B class genes showed both commonalities and diversifications with the conventional B-function described in the main model plants.

Effects of shoot pruning and inflorescence thinning on plant growth, yield and fruit quality of greenhouse tomatoes in a tropical climate

The combined effects of shoot pruning (one or two stems) and inflorescence thinning (five or ten flowers per inflorescence) on greenhouse tomato yield and fruit quality were studied during the dry season (DS) and rainy season (RS) in Central Thailand. Poor fruit set, development of undersized (mostly parthenocarpic) fruits, as well as the physiological disorders blossom-end rot (BER) and fruit cracking (FC) turned out to be the prevailing causes deteriorating fruit yield and quality. The proportion of marketable fruits was less than 10% in the RS and around 65% in the DS. In both seasons, total yield was significantly increased when plants were cultivated with two stems, resulting in higher marketable yields only in the DS. While the fraction of undersized fruits was increased in both seasons when plants were grown with a secondary stem, the proportions of BER and FC were significantly reduced. Restricting the number of flowers per inflorescence invariably resulted in reduced total yield. However, in neither season did fruit load considerably affect quantity or proportion of the marketable yield fraction. Inflorescence thinning tended to promote BER and FC, an effect which was only significant for BER in the RS. In conclusion, for greenhouse tomato production under climate conditions as they are prevalent in Central Thailand, the cultivation with two stems appears to be highly recommendable whereas the measures to control fruit load tested in this study did not proof to be advisable.

Water deficits promote flowering in Rhododendron via regulation of pre and post initiation development

Flowering is generally considered to be advanced by water deficits in many woody perennial species. A long-standing paradigm being that as a plant senses severe environmental conditions resources are diverted away from vegetative growth and towards reproduction before death. It is demonstrated that in Rhododendron flowering is promoted under water deficit treatments. However, the promotion of flowering is not achieved via all increase in floral initiation, but through separate developmental responses. If regulated deficit irrigation (RDI) is imposed prior to the time of initiation, fewer vegetative nodes are formed before the apical meristems switch to floral initiation, and chronologically, floral initiation occurs earlier. Both RDI and partial rootzone drying (PRD) treatments stimulate the development of more flowers Oil each inflorescence if the treatments are continued after the plant has undergone floral initiation. However, floral initiation is inhibited by soil water deficits. If the soil water deficit continues beyond the stages of floral development then anthesis call occur prematurely oil the fully formed floral buds without a need for a winter chilling treatment. It is hypothesised that inhibition of floral initiation in plants experiencing severe soil water deficits results from the inhibitory action Of ABA transportation to the apical meristem from stressed roots. It is demonstrated that ABA applications to well-watered Rhododendron inhibit floral initiation. (c) 2008 Elsevier B.V. All rights reserved.

Floral morphology and development in quillajaceae and surianaceae (Fabales), the species-poor relatives of leguminosae and polygalaceae

Background and Aims: Molecular phylogenies have suggested a new circumscription for Fabales to include Leguminosae, Quillajaceae, Surianaceae and Polygalaceae. However, recent attempts to reconstruct the interfamilial relationships of the order have resulted in several alternative hypotheses, including a sister relationship between Quillajaceae and Surianaceae, the two species-poor families of Fabales. Here, floral morphology and ontogeny of these two families are investigated to explore evidence of a potential relationship between them. Floral traits are discussed with respect to early radiation in the order. Methods: Floral buds of representatives of Quillajaceae and Surianaceae were dissected and observed using light microscopy and scanning electron microscopy. Key Results Quillajaceae and Surianaceae possess some common traits, such as inflorescence morphology and perianth initiation, but development and organization of their reproductive whorls differ. In Quillaja, initiation of the diplostemonous androecium is unidirectional, overlapping with the petal primordia. In contrast, Suriana is obdiplostemonous, and floral organ initiation is simultaneous. Independent initiation of five carpels is common to both Quillaja and Suriana, but subsequent development differs; the antesepalous carpels of Quillaja become fused proximally and exhibit two rows of ovules, and in Suriana the gynoecium is apocarpous, gynobasic, with antepetalous biovulate carpels. Conclusions: Differences in the reproductive development and organization of Quillajaceae and Surianaceae cast doubt on their potential sister relationship. Instead, Quillaja resembles Leguminosae in some floral traits, a hypothesis not suggested by molecular-based phylogenies. Despite implicit associations of zygomorphy with species-rich clades and actinomorphy with species-poor families in Fabales, this correlation sometimes fails due to high variation in floral symmetry. Studies considering specific derived clades and reproductive biology could address more precise hypotheses of key innovation and differential diversification in the order.

Floral meristem indeterminacy depends on flower position and is facilitated by acarpellate gynoecium development in Impatiens balsamina

Floral meristems are generally determinate. Termination of their activity varies with species, occurring after carpel or ovule development, depending on the placentation type. In terminal flowering Impatiens balsamina (cv. Dwarf Bush Flowered) some flowers exhibit meristem indeterminacy; they produce organs from the placenta after ovule development. Here we provide a detailed description of gynoecium development in this line and explore the basis of the indeterminate nature of some of its floral meristems. We find that the placenta is sometimes established without complete carpel fusion. Proliferative growth derives from meristematic remnants of the placenta and is more common in the terminal inflorescence. RNA in situ hybridization reveals that IbLFY (Impatiens LFY homologue) is expressed in all meristem states, even in proliferating meristems. Expression of IbAG in axillary flowers is as expected in the meristem, stamens and carpels but absent from the proliferating meristem. We conclude that I. balsamina has cauline placentation. Incomplete suppression of inflorescence identity in flowers of the terminal inflorescence leads to floral meristem proliferation after ovule development in this species.

Mechanisms and function of flower and inflorescence reversion

Flower and inflorescence reversion involve a switch from floral development back to vegetative development, thus rendering flowering a phase in an ongoing growth pattern rather than a terminal act of the meristem. Although it can be considered an unusual event, reversion raises questions about the nature and function of flowering. It is linked to environmental conditions and is most often a response to conditions opposite to those that induce flowering. Research on molecular genetic mechanisms underlying plant development over the last 15 years has pinpointed some of the key genes involved in the transition to flowering and flower development. Such investigations have also uncovered mutations which reduce floral maintenance or alter the balance between vegetative and floral features of the plant. How this information contributes to an understanding of floral reversion is assessed here. One issue that arises is whether floral commitment (defined as the ability to continue flowering when inductive conditions no longer exist) is a developmental switch affecting the whole plant or is a mechanism which assigns autonomy to individual meristems. A related question is whether floral or vegetative development is the underlying default pathway of the plant. This review begins by considering how studies of flowering in Arabidopsis thaliana have aided understanding of mechanisms of floral maintenance. Arabidopsis has not been found to revert to leaf production in any of the conditions or genetic backgrounds analysed to date. A clear-cut reversion to leaf production has, however, been described in Impatiens balsamina. It is proposed that a single gene controls whether Impatiens reverts or can maintain flowering when inductive conditions are removed, and it is inferred that this gene functions to control the synthesis or transport of a leaf-generated signal. But it is also argued that the susceptibility of Impatiens to reversion is a consequence of the meristem-based mechanisms controlling development of the flower in this species. Thus, in Impatiens, a leaf-derived signal is critical for completion of flowering and can be considered to be the basis of a plant-wide floral commitment that is achieved without accompanying meristem autonomy. The evidence, derived from in vitro and other studies, that similar mechanisms operate in other species is assessed. It is concluded that most species (including Arabidopsis) are less prone to reversion because signals from the leaf are less ephemeral, and the pathways driving flower development have a high level of redundancy that generates meristem autonomy even when leaf-derived signals are weak. This gives stability to the flowering process, even where its initiation is dependent on environmental cues. On this interpretation, Impatiens reversion appears as an anomaly resulting from an unusual combination of leaf signalling and meristem regulation. Nevertheless, it is shown that the ability to revert can serve a function in the life history strategy (perenniality) or reproductive habit (pseudovivipary) of many plants. In these instances reversion has been assimilated into regular plant development and plays a crucial role there.

Homologies of the flower and inflorescence in the early-divergent grass anomochloa (poaceae)

Premise of the study: The grass subfamily Anomochlooideae is phylogenetically significant as the sister group to all other grasses. Thus, comparison of their structure with that of other grasses could provide clues to the evolutionary origin of these characters. Methods: We describe the structure, embryology, and development of the flower and partial inflorescence of the monotypic Brazilian grass Anomochloa marantoidea. We compare these features with those of other early-divergent grasses such as Pharus and Streptochaeta and closely related Poales such as Ecdeiocolea. Key results: Anomochloa possesses several features that are characteristic of Poaceae, notably a scutellum, a solid style, reduced stamen number, and an ovary with a single ovule that develops into a single indehiscent fruit. Interpretation of floral patterning in Anomochloa is problematic because the ramification pattern of the florets places the bracts and axes in unusual positions relative to the primary inflorescence axis. Our study indicates that there is a single abaxial carpel in Anomochloa, probably due to a cryptic type of pseudomonomery in Anomochloa that resembles the pseudomonomery of other grasses. On the other hand, the Anomochloa flower differs from the typical grass flower in lacking lodicules and possessing four stamens, in contrast with the tristaminate condition that characterizes many other grasses. Conclusions: Using the median part of the innermost bract as a locator, we tentatively homologize the inner bract of the Anomochloa partial inflorescence with the palea of other grasses. In this interpretation, the pattern of monosymmetry due to stamen suppression differs from that of Ecdeiocolea. © 2012 Botanical Society of America.