Kai Wang, Zhengyu Shao , Feilong Guo, Ke Wang and Zengyan Zhang
　　Plant Physiology, IF: 7.394
　　doi:10.1093/plphys/kiab227
　　Abstract
　　Sharp eyespot disease, caused by the soil-borne fungus Rhizoctonia cerealis, seriously threatens production of wheat (Triticum
aestivum). Despite considerable advances in understanding the mechanisms of mitogen-activated protein kinase (MAPK) cascades
in innate immunity in model plant species, the roles of MAPK cascades in wheat are unknown. In this study, we identified
a wheat MAPK kinase TaMKK5, located on chromosome 6B, and deciphered its functional role in the innate immune responses
to R. cerealis attack. The TaMKK5-6B transcript level was elevated after R. cerealis infection and was higher in resistant wheat
genotypes compared to susceptible genotypes. Overexpressing TaMKK5-6B increased resistance to sharp eyespot and upregulated
the expression of multiple defense-related genes in wheat, including the MAPK gene TaMPK3, the ethylene response factor
gene TaERF3, the calcium-dependent protein kinase gene TaCPK7-D, the glutathione s-transferase-1 gene TaGST1, Defensin, and
Chitinase 2, while TaMKK5 knock-down compromised the resistance and repressed the expression of these defense-related genes.
Bimolecular fluorescence complementation, yeast two-hybrid, pull-down, and phosphorylation assays showed that TaMKK5
physically interacted with TaMPK3, and phosphorylated and activated TaMPK3, and that TaMPK3 interacted with and phosphorylated
TaERF3. The TaMKK5–TaMPK3 cascade modulates the expression of TaGST1, Defensin, and Chitinase 2 through
TaERF3. Collectively, TaMKK5 mediates resistance to sharp eyespot through the TaMKK5–TaMPK3–TaERF3 module and by
upregulating the expression of defense-related genes in wheat. This study provides insights into the role of the wheat MAPK cascades
in innate immunity. TaMKK5-6B is a promising gene for breeding wheat cultivars that are resistant to sharp eyespot.