Evolution and expression patterns of cytokinin oxidase genes in Fragaria vesca

- Eight cytokinin oxidase (CKX) genes are identified in woodland strawberry.
- Expansion patterns and functional divergence of FvCKX genes are characterized.
- FvCKX genes are differentially expressed in the organs at the reproductive stage.
- Most FvCKX genes are induced by drought, salt and ABA treatments, but not by heat.

Cytokinin oxidases/dehydrogenases (CKXs) are the only known enzymes that specifically catalyze the degradation of cytokinins (CKs). CKXs regulate CK levels in plants and play an essential role in CK regulatory processes. In spite of their physiological importance, systematic analyses of CKX genes in woodland strawberry, Fragaria vesca, have not been performed yet. In this paper, we report a genome-wide identification and characterization of FvCKX genes. A total of eight FvCKX genes were identified. Phylogenetic analysis showed that species-specific expansion of FvCKX genes have occurred, possibly through segmental duplication or single gene transposition-duplication. Various types of cis-elements detected in the promoters suggested a functional diversification of the FvCKX genes. Quantitative PCR assays were carried out, demonstrating differential expression patterns of FvCKX genes in the organs, under abiotic stresses including drought, salt and heat, and under abscisic acid (ABA) treatments. Most expressed FvCKXs exhibited relatively high expression in roots, stolons, leaves, flowers and young fruits. Significant induction of FvCKX genes was observed in leaves and roots under salt treatment, and in leaves under drought and ABA treatments, suggesting that CKs were negative regulators in strawberry responses to drought, salt and ABA. More FvCKX genes were repressed after heat treatment, indicating a possible different pattern of CK modulation under heat. Taken together, our results show moderate expansion and diverse expression patterns of FvCKX genes in woodland strawberry. This will help to enhance the understanding of functional divergence of these FvCKX genes and provide a basis for improving stress tolerance of strawberries by manipulating the CK content.