Functional Analysis of TAC4 and its Homolog TAC4L in Regulating Secondary Cell Wall Cellulose Biosynthesis in Rice

The secondary cell wall (SCW) is a crucial structural component in plants, providing mechanical strength and regulating developmental processes through intricate transcriptional regulatory networks. In this study, we identified TAC4L as a functional homolog of TAC4 in rice, which exhibits overlapping spatial–temporal expression patterns with TAC4. The tac4l tac4 double-knockout mutants exhibit a severe brittle phenotype distinct from their single mutants, underscoring their synergistic effect in SCW deposition. Based on RNA-Seq data and molecular biochemical assays, we propose a working hypothesis that both TAC4L and TAC4 directly bind to the OsMYB103L promoter, and physically interact with OsTCP19 to facilitate its expression. This putative activation cascade subsequently upregulates downstream SCW biosynthesis genes, including cellulose synthase genes ( OsCesAs ). These findings advances our understanding of the molecular mechanisms governing SCW biosynthesis and provide potential genetic targets for improving crop mechanical strength and biomass utilization.