Genome-wide identification of cytokinin oxidases/dehydrogenase (CKXs) in grape and expression during berry set

Cytokinin oxidase/dehydrogenase (CKX) is a flavoenzyme, which irreversibly degrades the cytokinins and plays an important role in plant growth and development. They have been identified in many plants, but little is known in grape. Also, how CKXs meditated cytokinin signal pathway in grape berry set process is unclear. In this study, a total of 8 VvCKX gene family members (GFMs) were identified from ‘Kyoho’ grape genome, which divided into four group (group I, II, III, IV) based on phylogenetic analysis. Further structural analysis found that all VvCKXs had 3–5 intron and VvCKX GFMs that clustered together according to a phylogenetic tree had similar motif. The CKX GFMs had two highly conserved domains: an oxidase FAD-binding domain and a cytokinin dehydrogenase 1, FAD/cytokinin binding domain. In addition, the 8 VvCKX GFMs distributed on 6 chromosome and chromosome mapping indicated that three group genes of VvCKX were identified segment duplication genes. Growth and development, light response, phytohormone responsive and abiotoc elements were identified from the cis-regulatory elements analysis of VvCKX GFMs. The expression profiles of VvCKX GFMs in different organs suggested that VvCKX4 and VvCKX8 had highly expression in inflorescence and may play important role in grape berry set. Furthermore, the expression of VvCKX GFMs following application of N-(2-chloro-4-pyridyl)-N'-phenylurea (CPPU) showed that the majority of VvCKX GFMs were up-regulated, especially VvCKX4, VvCKX6 and VvCKX8. But VvCKX5 was consistently down-regulated. These results indicate that VvCKX GFMs may play important role in the set of grape berries. Our results provide valuable information for future studies on the functional characteristics of VvCKX GFMs in grape berry set.