Genome-Wide Analysis of AGC Kinases Reveals that MoFpk1 Is Required for Development, Lipid Metabolism, and Autophagy in Hyperosmotic Stress of the Rice Blast Fungus Magnaporthe oryzae

Abstract

ABSTRACT During eukaryotic evolution, the TOR-AGC kinase signaling module is involved in the coordinated regulation of cell growth and survival. However, the AGC kinases in plant-pathogenic fungi remain poorly understood. In this study, we have identified 20 members of the AGC family of protein kinases. Evolutionary and biological studies have revealed that AGC kinases are highly conserved and involved in the growth (8 genes), conidiation (13 genes), conidial germination (9 genes), appressorium formation (9 genes), and pathogenicity (5 genes) of Magnaporthe oryzae, in which a subfamily protein of the AGC kinases, MoFpk1, the activator of flippase, specifically exhibited diverse roles. Two kinase sites were screened and found to be critical for MoFpk1: 230K and 326D. Moreover, MoFpk1 is involved in cell wall integrity through the negative regulation of MoMps1 phosphorylation. The deletion of MoFpk1 resulted in defective phosphatidylacetamide (PE) and phosphatidylserine (PS) turnover and a series of lipid metabolism disorders. Under hyperosmotic stress, since the ΔMofpk1 mutant is unable to maintain membrane asymmetry, MoYpk1 phosphorylation and MoTor activity were downregulated, thus enhancing autophagy. Our results provide insights into the evolutionary and biological relationships of AGC kinases and new insight into plasma membrane (PM) homeostasis, i.e., responses to membrane stress and autophagy through lipid asymmetry maintenance. IMPORTANCE Our identification and analysis of evolutionary and biological relationships provide us with an unprecedented high-resolution view of the flexible and conserved roles of the AGC family in the topmost fungal pathogens that infect rice, wheat, barley, and millet. Guided by these insights, an AGC member, MoFpk1, was found to be indispensable for M. oryzae development. Our study defined a novel mechanism of plasma membrane homeostasis, i.e., adaptation to stress through the asymmetric distribution of phospholipids. Furthermore, defects in the asymmetric distribution of phospholipids in the membrane enhanced autophagy under hyperosmotic stress. This study provides a new mechanism for the internal linkage between lipid metabolism and autophagy, which may help new fungicide target development for controlling this devastating disease.

Keywords

• Magnaporthe oryzae
• AGC kinases
• MoFpk1
• lipid metabolism
• autophagy