PdeMIXTA04 triggers epidermal cells of placenta to differentiate into poplar catkins through forming MBW complexes with PdeMYC and PdeWD40

Differentiation of plant epidermal cells is a keen research topic in plant biology. Our study on Populus deltoides revealed that epidermal cells of the female flower placenta protruded to form catkin fibers immediately after pollination. We discovered that PdeMIXTA04 was explicitly expressed in placenta of female poplar flowers. Heterologous expression of PdeMIXTA04 in Arabidopsis demonstrated that it significantly promoted the leaf epidermal cells to differentiate into trichomes. Compared with the wild type, significant increases in trichome density and trichome branches were observed on leaves of all 35S:PdeMIXTA04 transgenic lines. Furthermore, transformation of PdeMIXTA04 in the trichomeless Arabidopsis mutant (gl1) restored trichome development to that of the wild type. GUS expression in poplar, driven by the promoter of PdeMIXTA04, also confirmed trichome-specific expression. We then screened a yeast library with PdeMIXTA04 and captured two interacting genes, PdeMYC and PdeWD40. Interactions between these two proteins were verified by yeast two-hybrid (Y2H), biomolecular fluorescence complementation (BiFC), dual-luciferase (dual-LUC), and pull-down assays, indicating that PdeMIXTA04 functions through the MYB-BHLH-WD40 (MBW) ternary complex. Our work presents evidence of PdeMIXTA04 as a candidate gene for editing to resolve catkins associated pollution and provides distinctive understanding of the molecular mechanism triggering differentiation of plant epidermal cells.