The D-lactate dehydrogenase MoDLD1 is essential for growth and infection-related development in Magnaporthe oryzae

Rice blast disease caused by Magnaporthe oryzae is initiated by the attachment of conidia to plant surfaces. Germ tubes emerging from conidia develop melanized appressoria to physically penetrate the host surface. Previous studies revealed that appressorium development requires the breakdown of storage lipids and glycogen that occur in peroxisomes and the cytosol respectively, culminating in production of pyruvate. However, the downstream product(s) entering the mitochondria for further oxidation is unclear. In this study, we aimed to investigate the molecular basis underlying the metabolic flux towards the mitochondria associated with the infectious-related development in M. oryzae. We showed that D-lactate is a key intermediate metabolite of the mobilization of lipids and glycogen, and its oxidative conversion to pyruvate is catalysed by a mitochondrial D-lactate dehydrogenase MoDLD1. Deletion of MoDLD1 caused defects in conidiogenesis and appressorium formation, and subsequently the loss of fungal pathogenicity. Further analyses demonstrated that MoDLD1 activity is involved in the maintenance of redox homeostasis during conidial germination. Thus, MoDLD1 is a critical modulator that channels metabolite flow to the mitochondrion coupling cellular redox state, and contributes to development and virulence of M. oryzae.