OsABA3 is Crucial for Plant Survival and Resistance to Multiple Stresses in Rice

Preharvest sprouting (PHS) is a serious problem in rice production as it leads to reductions in grain yield and quality. However, the underlying mechanism of PHS in rice remains unclear. In this study, we identified and characterized a preharvest sprouting and seedling lethal (phssl) mutant. The heterozygous phssl/+ mutant exhibited normal plant development, but severe PHS in paddy fields. However, the homozygous phssl mutant was seedling lethal. Gene cloning and genetic analysis revealed that a point mutation in OsABA3 was responsible for the mutant phenotypes. OsABA3 encodes a molybdenum cofactor (Moco) sulfurase. The activities of the sulfureted Moco-dependent enzymes such as aldehyde oxidase (AO) and xanthine dehydrogenase (XDH) were barely detectable in the phssl mutant. As the final step of abscisic acid (ABA) de novo biosynthesis is catalyzed by AO, it indicated that ABA biosynthesis was interrupted in the phssl mutant. Exogenous application of ABA almost recovered seed dormancy of the phssl mutant. The knock-out (ko) mutants of OsABA3 generated by CRISPR-Cas9 assay, were also seedling lethal, and the heterozygous mutants were similar to the phssl/+ mutant showing reduced seed dormancy and severe PHS in paddy fields. In contrast, the OsABA3 overexpressing (OE) plants displayed a significant increase in seed dormancy and enhanced plant resistance to PHS. The AO and XDH activities were abolished in the ko mutants, whereas they were increased in the OE plants. Notably, the Moco-dependent enzymes including nitrate reductase (NR) and sulfite oxidase (SO) showed reduced activities in the OE plants. Moreover, the OE plants exhibited enhanced resistances to osmotic stress and bacterial blight, and flowered earlier without any reduction in grain yield. Taken together, this study uncovered the crucial functions of OsABA3 in Moco sulfuration, plant development, and stress resistance, and suggested that OsABA3 is a promising target gene for rice breeding.