Differential activity of CYTOKININ OXIDASE/DEHYDROGENASE3 (CKX3) and CKX5 genes in regulating yield components in Brassica napus L.

Cytokinin is a plant hormone that regulates several yield-related traits in plants. Previously, it was demonstrated that in tetraploid oilseed rape (Brassica napus L.), mutation of all four cytokinin-degrading BnCKX3 and both BnCKX5 genes resulted in increased cytokinin concentration, larger and more active inflorescence meristems, and a higher number of ovules per gynoecium. This resulted in the formation of more flowers and pods on the main stem, thereby increasing seed yield from the main stem of the plants. Here, we investigated the relative contributions of distinct combinations of BnCKX3 and BnCKX5 genes of the A and C genomes to these yield components. Our analysis revealed an unexpectedly strong role for BnCKX5 in regulating these traits and identified distinct supportive BnCKX3 gene mutant combinations. These findings facilitate the selection of relevant alleles for breeding. Furthermore, seeds from BnCKX gene mutant plants showed oil content and concentrations of unsaturated fatty acids similar to those of the wild type. Taken together, this study provides further insight into the role of cytokinin and BnCKX genes in regulating yield components in oilseed rape and provides novel information on functionally relevant alleles.