The role of cytokinin and CKX genes in regulating seed yield in barley and oilseed rape

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Due to the rapidly growing world population, stabilizing or increasing the yields of agricultural plants is of great importance. Regulation of crop yield is a complex process involving numerous genes, most of which are unknown. CKX genes have been shown to play a role in yield control in monocots and dicots. These genes code for proteins, which catalyze the breakdown of the plant hormone cytokinin. It is the aim of this proposal to investigate the role of certain CKX genes in barley (Hordeum vulgare L.) and oilseed rape (Brassica napus L.) in more detail. The first part of the project proposes to investigate the role of two genes, HvCKX2.1 and HvCKX2.2, which are related to the well-known yield gene OsCKX2 of rice, in yield formation in barley. Here, the focus is on the molecular and phenotypic characterization of corresponding Hvckx2.1 and Hvckx2.2 single and double mutants generated by genome editing. Mutant reproductive development and yield formation will be analyzed in the greenhouse and in the field, with a focus on spike and seed development. The second crop studied is oilseed rape, the most important oil crop in Europe. The applicant's research group has discovered two CKX genes that play a key role in controlling sink strength, which is important for high yields. The simultaneous inactivation of BnCKX3 and BnCKX5 leads to a higher cytokinin content and thereby to an activation of the inflorescence meristem and other reproductive tissues. This results in the formation of more flowers, more pods with more ovules, and ultimately a higher seed yield. In the proposed project, the reasons for a high oil content in the seeds of a specific Bnckx3,5 rapeseed mutant are to be investigated. Furthermore, the contribution of each of the six BnCKX3 and BnCKX5 alleles to yield formation in the greenhouse and in the field is analyzed. The effect of additional yield genes, which in particular increase source formation, is examined in oilseed rape and comparatively in Arabidopsis. Last but not least, the selection of CKX genes during domestication is explored in genomic data from wild, land and breeding lines of barley and oilseed rape.