Shade‐Induced Regulation of Cell Wall Thickening in Moso Bamboo: A Molecular Pathway Involving <i>XTH</i> Activity

How plants adapt to shade and perform specific morphogenesis is one of the secrets of the kingdom, and unravelling the underlying molecular mechanisms is crucial. Scanning electron microscope results have revealed that a low R/FR ratio (indicating shade conditions) inhibited the cell wall thickness of parenchyma cells and sieve tube cells of Moso bamboo (Phyllostachys edulis). Xyloglucan Endotransglucosylase/hydrolase3 (PheXTH3) was identified as a circadian rhythm gene responsive to a low R/FR ratio by qRT-PCR analysis, and it showed peak activity in the vascular system. PheXTH3 enhanced interfascicular fibre cell wall thickening and lignin accumulation in stable transgenic Arabidopsis thaliana lines. A low R/FR ratio downregulated PheXTH3 expression, subsequently suppressing cell wall thickening in vessel and interfascicular fibre cells. Both Yeast One-Hybrid experiments and Dual-LUC assays revealed that WOX3b1, AP2-39, and XTH3 may form a regulatory pathway. Collectively, we proposed a WOX3b1-AP2-39-XTH3 molecular pathway mediated by the ratio of low R/FR, which may regulate the thickening of cell wall in Moso bamboo.