OsMKKK70 Negatively Regulates Cold Tolerance at Booting Stage in Rice.

Cold stress at the booting stage leads to a lower seed setting rate and seriously threatens the production of rice ( L.), which has become a major yield-limiting factor in higher-altitude and -latitude regions. Because cold tolerance at the booting stage (CTB) is a complex trait and is controlled by multiple loci, only a few genes have been reported so far. In this study, a function of OsMKKK70 (Mitogen Activated Protein Kinase Kinase Kinase 70) in response to CTB was characterized. expression was rapidly induced by cold stress at the booting stage. overexpression () plants were more sensitive to cold stress at the booting stage with a lower seed setting and pollen fertility, but there was no significant difference between the mutant and WT. Considering the effect of functional redundancy, we further tested the CTB response of and , the double and triple mutants of with its closest homologs and , and found that and displayed significantly increased CTB with a higher seed setting and pollen fertility, indicating that OsMKKK70 negatively regulates rice CTB. Moreover, under the low-temperature (LT) condition, the mutant had slightly higher Gibberellin (GA) contents, increased expression of GA biosynthesis genes, and lower protein level of OsSLR1 in anthers than those in WT. By contrast, anther had a lower GA biosynthesis than that of WT. Together, these findings suggest that OsMKKK70 negatively regulates rice CTB by fine-tuning GA levels in anthers.