Phytochrome B modulates arsenite stress tolerance and arsenic accumulation in rice (Oryza sativa L.)

Arsenic (As) contamination severely limits plant growth and poses a significant threat to human health due to its accumulation in crops like rice. Phytochrome B (PhyB) regulates plant development and responses to abiotic stress, but its role in modulating As stress and regulating As accumulation in rice remains unclear. In this study, we examined the physiological and molecular responses of rice phytochrome B ( OsPHYB ) knockout ( OsPHYB -KO) lines compared with wild-type (WT) plants under arsenite [As(III)] stress. Under As(III) exposure for 7 days, OsPHYB -KO seedlings exhibited significantly increased root length (40.42 %-58.08 %), shoot height (7.41 %-9.22 %), and dry biomass (18.88 %-37.41 %) compared with WT. Chlorophyll fluorescence analysis showed enhanced photosynthetic efficiency in OsPHYB -KO lines, with significant increases in maximum photochemical efficiency of PSII (Fv/Fm) and effective photochemical quantum yield of PSII (φPSII). Notably, As concentrations in both shoots and roots of OsPHYB -KO plants were reduced by 39.78 %-51.89 % and 28.26 %-33.79 %, respectively, compared with WT. OsPHYB -KO lines had 25.56 %-55.63 % higher antioxidant enzyme activities and 43.10 %-54.60 % lower malondialdehyde levels, indicating improved tolerance to oxidative stress. Transcriptomic profiling and qRT-PCR revealed upregulation of genes involved in melatonin (MT) biosynthesis and glutathione (GSH) metabolism, with MT content increased by 16.20 %-67.96 % and GSH content elevated by 38.51 %-117.12 % in both roots and shoots of OsPHYB -KO plants. These results demonstrate that OsPHYB plays a crucial role in As(III) detoxification and provide a foundation for developing low-As rice cultivars.