Predicting Plant Performance Under Simultaneously Changing Environmental Conditions-The Interplay Between Temperature, Light, and Internode Growth

Plant performance is significantly influenced by prevailing light and temperature conditions during plant growth and development. For plants exposed to natural fluctuations in abiotic environmental conditions it is however laborious and cumbersome to experimentally assign any contribution of individual environmental factors to plant responses. This study aimed at analyzing the interplay between light, temperature and internode growth based on model approaches. We extended the light-sensitive virtual plant model L-Cucumber by implementing a common Arrhenius function for appearance rates, growth rates, and growth durations. For two greenhouse experiments, the temperature-sensitive model approach resulted in a precise prediction of cucumber mean internode lengths and number of internodes, as well as in accurately predicted patterns of individual internode lengths along the main stem. In addition, a system's analysis revealed that environmental data averaged over the experimental period were not necessarily related to internode performance. Finally, the need for a species-specific parameterization of the temperature response function and related aspects in modeling temperature effects on plant development and growth is discussed.

Complementation of the embryo-lethal T-DNA insertion mutant of AUXIN-BINDING-PROTEIN 1 (ABP1) with abp1 point mutated versions reveals crosstalk of ABP1 and phytochromes

The function of the extracytoplasmic AUXIN-BINDING-PROTEIN1 (ABP1) is largely enigmatic. We complemented a homozygous T-DNA insertion null mutant of ABP1 in Arabidopsis thaliana Wassilewskia with three mutated and one wild-type (wt) ABP1 cDNA, all tagged C-terminally with a strepII-FLAG tag upstream the KDEL signal. Based on in silico modelling, the abp1 mutants were predicted to have altered geometries of the auxin binding pocket and calculated auxin binding energies lower than the wt. Phenotypes linked to auxin transport were compromised in these three complemented abp1 mutants. Red light effects, such as elongation of hypocotyls in constant red (R) and far-red (FR) light, in white light supplemented by FR light simulating shade, and inhibition of gravitropism by R or FR, were all compromised in the complemented lines. Using auxin-or light-induced expression of marker genes, we showed that auxininduced expression was delayed already after 10 min, and light-induced expression within 60 min, even though TIR1/AFB or phyB are thought to act as receptors relevant for gene expression regulation. The expression of marker genes in seedlings responding to both auxin and shade showed that for both stimuli regulation of marker gene expression was altered after 10-20 min in the wild type and phyB mutant. The rapidity of expression responses provides a framework for the mechanics of functional interaction of ABP1 and phyB to trigger interwoven signalling pathways.

AUXIN-BINDING-PROTEIN1 (ABP1) in phytochrome-B-controlled responses

The auxin receptor ABP1 directly regulates plasma membrane activities including the number of PIN-formed (PIN) proteins and auxin efflux transport. Red light (R) mediated by phytochromes regulates the steady-state level of ABP1 and auxin-inducible growth capacity in etiolated tissues but, until now, there has been no genetic proof that ABP1 and phytochrome regulation of elongation share a common mechanism for organ elongation. In far red (FR)-enriched light, hypocotyl lengths were larger in the abp1-5 and abp1/ABP1 mutants, but not in tir1-1, a null mutant of the TRANSPORT-INHIBITOR-RESPONSE1 auxin receptor. The polar auxin transport inhibitor naphthylphthalamic acid (NPA) decreased elongation in the low R: FR light-enriched white light (WL) condition more strongly than in the high red: FR light-enriched condition WL suggesting that auxin transport is an important condition for FR-induced elongation. The addition of NPA to hypocotyls grown in R-and FR-enriched light inhibited hypocotyl gravitropism to a greater extent in both abp1 mutants and in phyB-9 and phyA-211 than the wild-type hypocotyl, arguing for decreased phytochrome action in conjunction with auxin transport in abp1 mutants. Transcription of FR-enriched light-induced genes, including several genes regulated by auxin and shade, was reduced 3-5-fold in abp1-5 compared with Col and was very low in abp1/ABP1. In the phyB-9 mutant the expression of these reporter genes was 5-15-fold lower than in Col. In tir1-1 and the phyA-211 mutants shade-induced gene expression was greatly attenuated. Thus, ABP1 directly or indirectly participates in auxin and light signalling.

Evaluation of reproductive barriers contributes to the development of novel interspecific hybrids in the Kalanchoe genus

Background: Interspecific hybridization is a useful tool in ornamental breeding to increase genetic variability and introduce new valuable traits into existing cultivars. The successful formation of interspecific hybrids is frequently limited by the presence of pre- and post-fertilization barriers. In the present study, we investigated the nature of hybridization barriers occurring in crosses between Kalanchoe species and evaluated possibilities of obtaining interspecific hybrids. Results: The qualitative and quantitative analyses of pollen tube growth in situ were performed following intra-and interspecific pollinations. They revealed occurrence of pre-fertilization barriers associated with inhibition of pollen germination on the stigma and abnormal growth of pollen tubes. Unilateral incongruity related to differences in pistil length was also observed. The pollen quality was identified as a strong factor influencing the number of pollen tubes germinating in the stigma. In relation to post-fertilization barriers, endosperm degeneration was a probable barrier hampering production of interspecific hybrids. Moreover, our results demonstrate the relation of genetic distance estimated by AFLP marker analysis of hybridization partners with cross-compatibility of Kalanchoe species. At the same time, differences in ploidy did not influence the success of interspecific crosses. Conclusions: Our study presents the first comprehensive analysis of hybridization barriers occurring within Kalanchoe genus. Reproductive barriers were detected on both, pre- and post-fertilization levels. This new knowledge will contribute to further understanding of reproductive isolation of Kalanchoe species and facilitate breeding of new cultivars. For the first time, interspecific hybrids between K. nyikae as maternal plant and K. blossfeldiana as well as K. blossfeldiana and K. marnieriana were generated.