Genome-wide identification and expression profiling of the YUCCA gene family in Malus domestica.

The plant hormone auxin is essential for plant growth and development. YUCCA proteins catalyse the rate-limiting step for endogenous auxin biosynthesis. In this study, we isolated 20 MdYUCCA genes from apple genome. MdYUCCA6a, MdYUCCA8a, and MdYUCCA10a were expressed in most organs and could support whole plant basal auxin synthesis. MdYUCCA4a, MdYUCCA10b, and MdYUCCA11a expression indicated roles for these genes in auxin biosynthesis in vegetative organs. MdYUCCA2b, MdYUCCA11b, and MdYUCCA11d were mainly expressed in flower organs. High temperature induced the expression of MdYUCCA4a, MdYUCCA6a, MdYUCCA8a, and MdYUCCA10a, and down-regulated the expression of MdYUCCA2b and MdYUCCA6b. Dual-luciferase assay indicated that MdPIF4 could trans-activate the MdYUCCA8a promoter. Overexpression of MdYUCCA8a increased IAA content, increased stem height, enhanced apical dominance, and led to silique malformation. These results provide a foundation for further investigation of the biological functions of apple MdYUCCAs.