University of Hohenheim

About: University of Hohenheim is a education organization based out in Stuttgart, Germany. It is known for research contribution in the topics: Population & Soil water. The organization has 8585 authors who have published 16406 publications receiving 567377 citations.

Mutual interaction of auxin and cytokinins in regulating correlative dominance

Abstract: Correlative dominance requires correlative signals from a dominant to a dominated organ. Auxins, particularly IAA, and cytokinins are obviously important components of this correlative system. Using a vegetative pea shoot and a generative apple and tomato fruit system it can be demonstrated that dominant organs always export more IAA and have a higher 3H-IAA transport capacity and velocity compared to dominated organs. In both systems the dominant organ can be replaced by the application of auxin, e.g. NAA, which maintains the differences in IAA export. This is an indication that similar regulatory mechanisms control dominance in both of these diverse systems. The possibility of replacing a dominant organ by auxin also makes it unlikely that growth of that organ or allocation of nutrients regulates the correlative inhibition of the dominated organ.It is suggested that differences in IAA export from, and transport capacities of, dominant and dominated shoots, may be explained by a mechanism of auxin transport autoinhibition (ATA), whereby the earlier and stronger export of IAA from the dominant shoot inhibits auxin export from the dominated shoot at the point where the two auxin streams converge. This hypothesis was tested with explants of pea, apple and tomato. It was shown that the basal application of cold IAA significantly reduced endogenous as well as exogenous IAA transport through these explants.Since the reduced IAA transport of dominated organs was not followed by an accumulation of IAA in the auxin producing subtending organ, it was concluded that IAA biosynthesis was possibly reduced and/or IAA conjugation stimulated. This could have been one of the determinants of their growth inhibition. ATA might also explain how the unidirectional IAA signal may affect the growth rate of organs even lateral or acropetal to its transport pathway and thus polar IAA-transport becomes a ``multidirectional'' signal. From the experiments demonstrated it seems that ATA is a sufficient mechanism to impose growth inhibition in the dominated organ, without the need of other regulators.However, to release dominated organs from dominance cessation of ATA may not be sufficient and cytokinins are obviously a powerful antagonist to auxins. Their repeated exogenous application turns dominated lateral buds into strongly growing organs which ultimately may even dominate the previously dominant apex. These lateral shoots finally gain a strong IAA export capacity and inhibit, by ATA, IAA export from the hitherto dominant apex.In other experiments it was shown that interruption of polar IAA transport leads to a strong increase in root derived cytokinins. This can largely be prevented, in a concentration dependent manner, by the application of auxin, indicating that basipolar auxin may control cytokinin production in the roots and its possible delivery to lateral buds. In turn, the increased delivery of cytokinins to the lateral buds promotes a strong increase in IAA production and export. Thus there is a strong mutual interaction between auxin production in the shoots and cytokinin production in the roots, which may be important in regulating the balance between root and shoot growth.

Variation explained in mixed-model association mapping

Abstract: Genomic mapping of complex traits across species demands integrating genetics and statistics. In particular, because it is easily interpreted, the R(2) statistic is commonly used in quantitative trait locus (QTL) mapping studies to measure the proportion of phenotypic variation explained by molecular markers. Mixed models with random polygenic effects have been used in complex trait dissection in different species. However, unlike fixed linear regression models, linear mixed models have no well-established R(2) statistic for assessing goodness-of-fit and prediction power. Our objectives were to assess the performance of several R(2)-like statistics for a linear mixed model in association mapping and to identify any such statistic that measures model-data agreement and provides an intuitive indication of QTL effect. Our results showed that the likelihood-ratio-based R(2) (R(LR)(2)) satisfies several critical requirements proposed for the R(2)-like statistic. As R(LR)(2) reduces to the regular R(2) for fixed models without random effects other than residual, it provides a general measure for the effect of QTL in mixed-model association mapping. Moreover, we found that R(LR)(2) can help explain the overlap between overall population structure modeled as fixed effects and relative kinship modeled though random effects. As both approaches are derived from molecular marker information and are not mutually exclusive, comparing R(LR)(2) values from different models provides a logical bridge between statistical analysis and underlying genetics of complex traits.

Association mapping for quality traits in soft winter wheat

Abstract: Improvement of end-use quality in bread wheat (Triticum aestivum L.) depends on a thorough understanding of the genetic basis of important quality traits. The main goal of our study was to investigate the genetic basis of 1,000-kernel weight, protein content, sedimentation volume, test weight, and starch concentration using an association mapping approach. We fingerprinted 207 diverse European elite soft winter wheat lines with 115 SSR markers and evaluated the genotypes in multi-environment trials. The principal coordinate analysis revealed absence of a clear population but presence of a family structure. Therefore, we used linear mixed models and marker-based kinship matrices to correct for family structure. In genome-wide scans, we detected main effect QTL for all five traits. In contrast, epistatic QTL were only observed for sedimentation volume and test weight explaining a small proportion of the genotypic variation. Consequently, our findings suggested that integrating epistasis in marker-assisted breeding will not lead to substantially increased selection gain for quality traits in soft winter wheat.