Identification of the flavin-dependent monooxygenase-encoding YUCCA gene family in Populus trichocarpa and their expression in vegetative tissues and in response to hormone and environmental stresses

Auxin is a plant hormone that regulates many processes of plant growth such as apical dominance, cell growth, adventitious rooting, and fruit and seed development. Expression of a family of YUCCA genes important for auxin biosynthesis has been shown to be spatially and temporally regulated in Arabidopsis. In this study, we report on the identification of 12 YUCCA genes from the completely sequenced Populustrichocarpa genome database and characterized them by comparing them with ArabidopsisYUCCA genes. The PopulusYUCCA genes are distributed on eight chromosomes. All Populus and Arabidopsis YUCCA genes can be divided into two phylogenetic groups, one of which can be divided into two subgroups. Populus YUCCA genes are expressed in the shoot tip, immature and mature leaf, young root, stem, and bark tissues in an tissue-specific manner. Transcript accumulation of the Populus YUCCA genes is reduced by exogenous applications of various plant growth regulators except auxin. Steady-state mRNA levels of different Populus YUCCA genes vary considerably depending on the experimental treatments. These results suggest that, similar to the Arabidopsis and rice YUCCA genes, the Populus YUCCA genes may also have diversified roles in Populus growth and development, and their expression may be regulated in a complex manner by developmental and environmental cues.