Genome-wide investigation of cytokinin oxidase/dehydrogenase (CKX) family genes in Brassica juncea with an emphasis on yield-influencing CKX

Rapeseed mustard (Brassica juncea) is an important edible oilseed crop whose yield is impacted not only by the biotic and abiotic stresses but the low productivity of the cultivars also has a great impact over it. In the past, cytokinin oxidase/dehydrogenase (CKX) family gene manipulation has increased yield and stress tolerance and has been cloned and characterized in different plant species. Cytokinin oxidase/dehydrogenase (CKX) is an important enzyme regulating cytokinin homeostasis and regulating the yield and tolerance traits in plants. This study demonstrated a comprehensive investigation of the CKX gene family in B. juncea cv. Varuna. As a result, a total of 24 CKX genes were identified across the 36 chromosomes (AABB) and classified into seven distinct subgroups. These seven subgroups were annotated based on their homology with their counterparts present in Arabidopsis thaliana. Expression pattern analysis by RT-qPCR in the high-and low-yielding B. juncea cultivars showed that all 24 CKX expressed differentially in various tissues; most were expressed in leaves, stems and developing siliques. The two functional domains, FAD-binding and Cytokinin-binding domains required for CKX activity, were conserved across the CKX family genes. Our findings systematically revealed the evolutionary dynamics of the BjCKX family genes. They led the foundation for subsequent validation of the CKX for their functional role in yield enhancement in B. juncea.