The LPA1-ITA1-BRXL4 module regulates shoot gravitropism and tiller angle in rice

Tiller angle is a critical agronomic trait influencing rice plant architecture and yield potential. However, the molecular mechanisms underlying its regulation remain incompletely understood. Here, we report that ITA1 (LOC_Os01g51260), encoding a MYB family transcription factor, positively regulates shoot gravitropism and restricts tiller angle in rice. The ita1 mutant, characterized by a 740-bp deletion in the ITA1 promoter, displays an enlarged tiller angle due to elevated ITA1 expression. Functional assays demonstrate that ITA1 directly activates BRXL4, a gene that modulates auxin transport by influencing the subcellular localization of LAZY1, a key regulator of shoot gravitropism. Yeast one-hybrid, ChIP-qPCR, EMSA, and luciferase assays reveal that the transcriptional repressor LPA1, a member of the IDD family, directly binds to the 740-bp region of the ITA1 promoter to repress its expression. Genetic evidence shows that the lpa1 mutant phenocopies ita1 and that the lpa1/ita1-c1 double mutant partially rescues the large tiller angle phenotype. Together, our findings define a previously unknown LPA1-ITA1-BRXL4 regulatory cascade that controls shoot gravitropism and tiller angle by modulating auxin distribution. This study provides new insights into plant architectural regulation and offers potential genetic targets for optimizing rice planting density and yield.