OsBOR1 Mediating Boron Efflux Controls Panicle Development via ROS Homeostasis in Rice

Panicle development is a critical determinant of the grain yield in rice ( Oryza sativa ). In this study, we identified a bor1 mutant ( boron transporter 1 ), which exhibits severe defects in panicle development. Bulked segregant analysis sequencing, genetic complementation, and gene knockout experiments demonstrated that OsBOR1 corresponds to LOC_Os12g37840. OsBOR1 encodes a boron efflux transporter that localizes to the plasma membrane and is highly expressed in roots and panicles. Disruption of the OsBOR1 function resulted in altered boron distribution among stems, leaves, and panicles, indicating a loss of boron homeostasis. Transcriptome analysis of the bor1 mutant revealed a significant enrichment of differentially expressed genes associated with primary metabolism, secondary metabolic processes, and oxidative stress responses. Consistently, elevated reactive oxygen species levels were observed in the mutant. Together, these results demonstrate that OsBOR1 is required for maintaining normal panicle development in rice, likely through the regulation of boron homeostasis and reactive oxygen species balance.