The expression of Aldo-keto reductase gene OsKOB1 coordinates ABA homeostasis and antioxidant defense to maintain seed vigor under osmotic stress.

Successful initiation of seed germination is essential for rice production. However, rice seed germination is highly sensitive to osmotic stresses such as high salinity and drought. The aldo/keto reductase (AKR) superfamily governs key physiological processes in plants, including substance metabolism, growth regulation, and stress adaptation etc. However, the dynamics of AKR conferring tolerance to osmotic stress in rice seeds during germination remain unclear. In this paper, we investigated the function of the rice AKR gene OsKOB1 under osmotic stress. RT-qPCR results showed that rice AKR gene OsKOB1 was highly expressed in rice embryos, young roots, and flowers under normal conditions, and was significantly up-regulated under salt and drought stress. The promoter region of OsKOB1 contains elements that respond to abscisic acid (ABA), salt, and drought stress, such as ABRE, ARE, W-box, DPBF, and ACGTATERD1 cis-elements. Phenotypic comparisons demonstrated that OsKOB1 mutant seeds exhibited compromised tolerance to salt and drought, delayed germination, elevated ABA and malondialdehyde (MDA) levels, and reduced proline accumulation and antioxidant enzyme activity compared to wild-type (WT) and OsKOB1-overexpressing lines. Furthermore, OsKOB1 expression correlated with synergistic changes in its interacting partners OsPER1 and Os07g0633100 in WT, oskob1, and OsKOB1-overexpressed seeds, implying coordinated regulation of stress-responsive pathways. Collectively, our findings highlight OsKOB1 expression as a key regulator of rice seed germination under osmotic stress, modulating ABA homeostasis, osmoprotectant biosynthesis, and antioxidant defense to enhance stress resilience. This study provides novel insights into AKR-mediated stress adaptation mechanisms in crops.