The effect of temperature stress on recombination in barley
Plant breeding is ultimately dependent on the process of recombination which is responsible for the generation of different genotypes with new allelic combinations. The control of meiotic recombination is increasingly being considered as a possible means of aiding plant breeding to tackle the challenges that it faces, such as the effect of linkage drag. Plant breeding could benefit from controlling meiotic recombination in many ways, as increasing the crossover (CO) frequency and changing CO distribution would help to break up current linkage blocks, which could facilitate introgression of exotic alleles or potentially release useful genetic variation. Such tools would also facilitate related academic tasks such as genetic mapping and cloning. Given the particular nature of its genome structure, barley is a crop that could particularly profit from the breaking up of established linkage blocks, which potentially constitute a bottleneck in breeding as it is estimated that around 25-30% of genes rarely recombine. The present study was initiated following previous studies that indicated that heat stress could increase and change the distribution of COs in barley. This phenomenon was confirmed in the initial experiments of present work by a long temperature treatment. However, the application of this phenomenon in a practical context was complicated by the need to target the heat stress to the correct meiotic stage of the plants to keep the impact on fertility to a minimum. In order to achieve this, a modular tray growing system has been investigated, which allowed a considerable improvement in the accuracy of the application of targeted temperature treatments. This system was used to apply short heat and cold treatments, which showed an increase and decrease in the frequency of COs in pericentromeric regions respectively. This approach is the first complete demonstration of the utility of the application of temperature in a breeding context, as the temperature effect was shown to affect the phenotypic variability observed in a field trial with the progeny of the treated plants. In addition to the modular tray growing system used, a spike and meiosis prediction model based on whole plant phenotypes is proposed, which could have application in multiple studies of meiosis in barley. Furthermore, this working platform was used as a baseline for an anther transcription experiment under heat stress, which highlighted interesting transcriptional changes, and the role of heat shock proteins such as HSP70 and HSP90, and the differential expression of some meiosis-related genes. The heat stress treatment has been also studied in other barley genotypic backgrounds, pointing to a potential variability in the heat stress resistance during meiosis, in terms of final fertility. Overall, this work studies the influence of temperature in recombination in barley and extends this to the unrelated crop sugar beet. It proposes a working platform for the application of abiotic stress in a breeding context for barley. This platform has also utility as a research tool for investigations into the underlying mechanisms of this phenomenon, with studies carried out on the transcription changes of anthers under heat stress and others on the variability of a diverse germplasm for maintenance of fertility under heat stress.
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