The Intermediates in Branched-Chain Amino Acid Biosynthesis Are Indispensable for Conidial Germination of the Insect-Pathogenic Fungus Metarhizium robertsii

Abstract

Branched-chain amino acid (BCAA) metabolism plays a significant role in many biological activities beyond protein synthesis. Spore germination initiates the first stage of vegetative growth, which is critical for the virulence of pathogenic fungi. In this study, we demonstrated that the keto-acid reductoisomerase MrILVC, a key enzyme for BCAA biosynthesis, from the insect-pathogenic fungus Metarhizium robertsii is associated with conidial germination and fungal pathogenicity. Surprisingly, the germination of the Δ MrilvC mutant was restored when supplemented with the intermediates of BCAA metabolism rather than three BCAAs. The result was significantly different from that of plant-pathogenic fungi. Therefore, this report highlights that the intermediates in BCAA biosynthesis are indispensable for conidial germination of M. robertsii .