OsMAPKKK69 Negatively Regulates Resistance to Blast and Bacterial Blight Diseases in Rice (Oryza sativa L.)

Rice blast is one of the main diseases of rice, causing severe economic losses to agricultural production; thus, the search for blast resistance is a top priority for rice breeding. When challenged by the blast causal fungus <i>Magnaporthe oryzae</i> the expression level of <i>OsMAPKKK69</i> gene in rice cultivar Nipponbar was found to increase significantly. Such an induction was also found in a different genetic material, cultivar Shufanggaonuo, indicating that <i>OsMAPKKK69</i> plays an important role in blast disease response. However, the function of <i>OsMAPKKK69</i> remains unclear. In this study, wild type ZH11 was selected as the background material to investigate the expression and functions of <i>OsMAPKKK69</i> in rice disease resistance by constructing knockout mutants. The results showed that <i>OsMAPKKK69</i> is mainly expressed in <i>four-week-old shoots</i> and localized in cell membrane, cytoplasm, and nucleus. The two allelic knockout mutants, <i>osmapkkk69-1</i> and <i>osmapkkk69-2</i>, were more resistant to <i>M. oryzae</i> and bacterial blight <i>Xanthomonas oryzae</i> pv. <i>Oryzae</i> (<i>Xoo</i>). Further agronomic trait analysis revealed that the <i>osmapkkk69-1</i> and <i>osmapkkk69-2</i> mutants had reduced plant height, smaller grain size, a significant increase in tillering number, but also a significant increase in yield per plant. Our results show that <i>OsMAPKKK69</i> is involved in the immune response of rice by negatively regulating the resistance to rice blast and blight diseases, and in regulating important agronomic traits. This study lays a foundation for revealing the molecular mechanism of <i>OsMAPKKK69</i> in the immune response to rice diseases and provides novel genetic resources for rice breeding.