Uncoupling of nutrient metabolism and cellular redox by cytosolic routing of the mitochondrial G-3-P dehydrogenase Gpd2 causes loss of conidiation and pathogenicity in Pyricularia oryzae

Oxidation of self-stored carbohydrates and lipids provides the energy for the rapid morphogenetic transformation during asexual and infection-related development in Pyricularia oryzae, which results in intracellular accumulation of reducing equivalents NADH and FADH₂, requiring a cytosolic shuttling machinery towards mitochondria. Our previous studies identified the mitochondrial D-lactate dehydrogenase MoDld1 as a regulator to channel the metabolite flow in conjunction with redox homeostasis. However, the regulator(s) facilitating the cytosolic redox balance and the importance in propelling nutrient metabolite flow remain unknown. The G-3-P shuttle is a conserved machinery transporting the cytosolic reducing power to mitochondria. In P. oryzae, the mitochondrial G-3-P dehydrogenase Gpd2 was required for cellular NAD⁺/NADH balance and fungal virulence. In this study, we re-locate the mitochondrial G-3-P dehydrogenase Gpd2 to the cytosol for disturbing cytosolic redox status. Our results showed overexpression of cytosolic gpd2^Δmts without the mitochondrial targeted signal (MTS) driven by Ribosomal protein 27 promoter (PR27) exerted conflicting regulation of cellular oxidoreductase activities compared to the ΔModld1 deletion mutant by RNA-seq and prevented the conidiation and pathogenicity of P. oryzae. Moreover, overexpression of gpd2^Δmts caused defects in glycogen and lipid mobilization underlying asexual and infectious structural development associated with decreased cellular NADH production and weakened anti-oxidation activities. RNA-seq and non-targeted metabolic profiling revealed down-regulated transcriptional activities of carbohydrate metabolism and lower abundance of fatty acids and secondary metabolites in RP27:gpd2^Δmts. Thus, our studies indicate the essential role of cytosolic redox control in nutrient metabolism fueling the asexual and infection-related development in P. oryzae.