Tight Genetic Linkage of Prezygotic Barrier Loci Creates a Multifunctional Speciation Island in Petunia

Most flowering plants depend on animal vectors for pollination and seed dispersal. Differential pollinator preferences lead to premating isolation and thus reduced gene flow between interbreeding plant populations [1, 2, 3 and 4]. Sets of floral traits, adapted to attract specific pollinator guilds, are called pollination syndromes [5]. Shifts in pollination syndromes have occurred surprisingly frequently [6], considering that they must involve coordinated changes in multiple genes affecting multiple floral traits. Although the identification of individual genes specifying single pollination syndrome traits is in progress in many species, little is known about the genetic architecture of coadapted pollination syndrome traits and how they are embedded within the genome [7]. Here we describe the tight genetic linkage of loci specifying five major pollination syndrome traits in the genus Petunia: visible color, UV absorption, floral scent production, pistil length, and stamen length. Comparison with other Solanaceae indicates that, in P. exserta and P. axillaris, loci specifying these floral traits have specifically become clustered into a multifunctional “speciation island” [ 8 and 9]. Such an arrangement promotes linkage disequilibrium and avoids the dissolution of pollination syndromes by recombination. We suggest that tight genetic linkage provides a mechanism for rapid switches between distinct pollination syndromes in response to changes in pollinator availabilities.

Stable two-element control of dTph1 transposition in mutator strains of Petunia by an inactive ACT1 introgression from a wild species

The high copy dTph1 transposon system of Petunia (Solanaceae) is one of the most powerful insertion mutagens in plants, but its activity cannot be controlled in the commonly used mutator strains. We analysed the regulation of dTph1 activity by QTL analysis in recombinant inbred lines of the mutator strain W138 and a wild species (P. integrifolia spp. inflata). Two genetic factors were identified that control dTph1 transposition. One corresponded to the ACT1 locus on chromosome I. A second, previously undescribed locus ACT2 mapped on chromosome V. As a 6-cM introgression in W138, the P. i. inflata act1(S6) allele behaved as a single recessive locus that fully eliminated transposition of all dTph1 elements in all stages of plant development and in a heritable fashion. Weak dTph1 activity was restored in act1(S6)/ACT2(S6) double introgression lines, indicating that the P. i. inflata allele at ACT2 conferred a low level of transposition. Thus, the act1(S6) allele is useful for simple and predictable control of transposition of the entire dTph1 family when introgressed into an ultra-high copy W138 mutator strain. We demonstrate the use of the ACT1(W138)/act1(S6) allele pair in a two-element dTph1 transposition system by producing 10 000 unique and fixed dTph1 insertions in a population of 1250 co-isogenic lines. This Petunia system produces the highest per plant insertion number of any known two-element system, providing a powerful and logistically simple tool for transposon mutagenesis of qualitative as well as quantitative traits.

Plant elicitor peptides are conserved signals regulating direct and indirect antiherbivore defense

Insect-induced defenses occur in nearly all plants and are regulated by conserved signaling pathways. As the first described plant peptide signal, systemin regulates antiherbivore defenses in the Solanaceae, but in other plant families, peptides with analogous activity have remained elusive. In the current study, we demonstrate that a member of the maize (Zea mays) plant elicitor peptide (Pep) family, ZmPep3, regulates responses against herbivores. Consistent with being a signal, expression of the ZmPROPEP3 precursor gene is rapidly induced by Spodoptera exigua oral secretions. At concentrations starting at 5 pmol per leaf, ZmPep3 stimulates production of jasmonic acid, ethylene, and increased expression of genes encoding proteins associated with herbivory defense. These include proteinase inhibitors and biosynthetic enzymes for production of volatile terpenes and benzoxazinoids. In accordance with gene expression data, plants treated with ZmPep3 emit volatiles similar to those from plants subjected to herbivory. ZmPep3-treated plants also exhibit induced accumulation of the benzoxazinoid phytoalexin 2-hydroxy-4,7-dimethoxy-1,4-benzoxazin-3-one glucoside. Direct and indirect defenses induced by ZmPep3 contribute to resistance against S. exigua through significant reduction of larval growth and attraction of Cotesia marginiventris parasitoids. ZmPep3 activity is specific to Poaceous species; however, peptides derived from PROPEP orthologs identified in Solanaceous and Fabaceous plants also induce herbivory-associated volatiles in their respective species. These studies demonstrate that Peps are conserved signals across diverse plant families regulating antiherbivore defenses and are likely to be the missing functional homologs of systemin outside of the Solanaceae.

The Molecular Characterization of a Predicted Glycosyltransferase from Lycopersicon esculentum

The synthesis of the plant cell wall is very complex, and understanding how this process occurs will lead to many benefits for future research and industries dependent upon cell walls for their products. The recent discovery of the functions of AtMUR3 and AtGT18 in Arabidopsis thaliana as xyloglucan galactosyltransferases has led to the identification of many more putative glycosyltransferases in the Arabidopsis genome. Due to the structural differences between the xyloglucans of Arabidopsis and solanaceous plants, we decided to search for putative arabinosyltransferases in the Solanaceae. Solanaceous xyloglucan is substituted by one to two arabinosyl residues at the second xylose position, and sometimes contains an arabinose at the first xylose position. In contrast, Arabidopsis xyloglucan does not contain arabinose, and is substituted by galactose at the second and third xylose position. Furthermore, the second galactose residue in Arabidopsis xyloglucan is usually fucosylated, a modification not found in solanaceous plants. Searching the database of expressed sequence tags (dbEST), we identified many likely glycosyltransferases in solanaceous plants, including tomato (Lycopersicon esculentum). AtMUR3 and AtGT18 search queries resulted in the identification of three putative glycosyltransferases in L. esculentum, which were tentatively designated LeGT1, Le1GT18, and Le2GT18. Based on phylogenetic considerations, Le2GT18 was thought to be a putative arabinosyltransferase. The gene was transformed into atmur3-3 and atgt18 mutant plants, and the resulting plants will be screened for homozygous plants with the inserted gene. The homozygous T2 plants can then be screened for changes in the composition of their cell walls. Because Le2GT18 is thought to be an arabinosyltransferase, the levels of arabinose may be increased in the xyloglucan fraction of the cell wall. If so, further testing can be performed to reveal the true function of Le2GT18.

Physalis viscosa : un nuevo hospedero de Leveillula taurica en Argentina

Leveillula taurica (Lév.) Salm. es un hongo patógeno que se encuentra actualmente en expansión en nuestro país y en particular en la provincia de Mendoza. Physalis viscosa (camambú) es una especie muy difundida en Argentina. La misma es principalmente una maleza que crece espontáneamente en numerosos cultivos de interés económico y en sus alrededores. El hallazgo de L. taurica sobre una especie tan difundida fue el motivo de su estudio. Los síntomas característicos observados fueron parches cuneiformes amarillos en la cara adaxial de las hojas y en correspondencia con los mismos, en la abaxial se presentó un afelpado blanquecino formado por las fructificaciones asexuales del patógeno. El estudio etiológico realizado mediante la histopatología de los órganos afectados y la morfometría del patógeno confirmó la presencia del hongo parásito obligado Leveillula taurica (Lév.) Salm., en su forma anamórfica Oidiopsis taurica Sal. [= Oidiopsis sicula (Scal)]. La enfermedad en el camambú se ha difundido en forma importante en la provincia de Mendoza desde su primer hallazgo en el departamento de Tupungato en 1996. Se encuentra presente desde diciembre hasta mayo. Este prolongado período puede representar una importante fuente de inóculo para cultivos susceptibles al patógeno. La presente constituye la primera cita, no sólo a nivel nacional sino también mundial, de L. taurica sobre Physalis viscosa.

Los árboles y arbustos indígenas cultivados como ornamentales en la ciudad de Mendoza y alrededores

En el presente trabajo los autores pasan en revista treinta y cuatro representantes indígenas de la Flora Argentina cultivados como ornamentales en la ciudad de Mendoza y alrededores, señalando su ubicación en parques, plazas, calles y paseos y aportando datos sobre fuste, floración, fructificación y viabilidad de sus semillas en base a observaciones directas de muchos años y a materiales de herbario, reunidos al efecto.

Los árboles indígenas cultivados en la ciudad de San Juan

Uno de los efectos de la catástrofe que en mil novecientos cuarenta y cuatro, destruyera la ciudad de San Juan, ha sido el de poner en descubierto la flora endrológica cultivada en los predio urbanos, que no podía ser vista por el viajero, antes de aquella fecha. El autor hace una clasificación preliminar de la misma, ocupándose de forma preferente de la flora autóctona representada por diez y siete especies indígenas que enumera, muchas de las cuales están documentadas con ejemplares de herbario, citado, o fotografías que ilustran el trabajo. Una corta lista de veinticuatro especies no indígenas, cultivadas, totalizan cuarenta y una especie arbóreas cultivadas, que menciona, en forma preliminar, para la ciudad de San Juan.

Palynological and geochemical data of sediment core GeoB3910-2 located offshore Northeast Brazil

High resolution palynological and geochemical data of sediment core GeoB 3910-2 (located offshore Northeast Brazil) spanning the period between 19 600 and 14 500 calibrated year bp (19.6-14.5 ka) show a land-cover change in the catchment area of local rivers in two steps related to changes in precipitation associated with Heinrich Event 1 (H1 stadial). At the end of the last glacial maximum, the landscape in semi-arid Northeast Brazil was dominated by a very dry type of caatinga vegetation, mainly composed of grasslands with some herbs and shrubs. After 18 ka, considerably more humid conditions are suggested by changes in the vegetation and by Corg and C/N data indicative of fluvial erosion. The caatinga became wetter and along lakes and rivers, sedges and gallery forest expanded. The most humid period was recorded between 16.5 and 15 ka, when humid gallery (and floodplain) forest and even small patches of mountainous Atlantic rain forest occurred together with dry forest, the latter being considered as a rather lush type of caatinga vegetation. During this humid phase erosion decreased as less lithogenic material and more organic terrestrial material were deposited on the continental slope of northern Brazil. After 15 ka arid conditions returned. During the humid second phase of the H1 stadial, a rich variety of landscapes existed in Northeast Brazil and during the drier periods small pockets of forest could probably survive in favorable spots, which would have increased the resilience of the forest to climate change.