Genome-Wide Identification of Poplar YABBY Transcription Factors Reveals Dual Roles of PtoYABBY6 in Leaf Polarity and Floral Initiation.

Abstract

YABBY transcription factors are an essential class of plant-specific macromolecules that regulate cellular processes, response to stress, secondary metabolite biosynthesis, and developmental regulation. Despite their significance in plant macromolecular networks, their roles in woody perennials remain underexplored. In this study, we identified and classified 13 YABBY proteins from Populus trichocarpa and 22 YABBY proteins from P. tomentosa into five distinct subfamilies. Subsequently, we constructed a phylogenetic tree based on the YABBY proteins of five plant species, and we analyzed the conserved structural domains, motifs, promoter regions, and collinearity of the poplar YABBYs. Expression patterns of the poplar YABBYs were characterized in vegetative organs and male/female flower buds. The results indicated that PtoYABBY6 is predominantly expressed in reproductive organs, with higher expression levels observed in female flower buds compared to male flower buds. Functional analysis of PtoYABBY6 demonstrated that its overexpression in Arabidopsis thaliana led to partial alterations in the adaxial-abaxial axis polarity of leaves and delayed flowering. Additionally, the expression levels of FLOWERING LOCUS T (FT), a gene associated with flowering time, as well as FILAMENTOUS FLOWER (FIL), KANADI (KAN), REVOLUTA (REV), and PHAVOLUTA (PHV; genes related to leaf adaxial-abaxial polarity) were altered in Arabidopsis. Furthermore, transient overexpression of PtoYABBY6 in poplar leaves induced subtle changes in adaxial epidermal cell morphology and increased the palisade-to-spongy tissue ratio, providing partial evidence suggesting a potential role in leaf development within a poplar cellular context. These findings provide a foundation for future functional studies and contribute to a better understanding of the molecular mechanisms underlying YABBY protein functions in poplar.