The methionine biosynthesis regulator AaMetR contributes to oxidative stress tolerance and virulence in Alternaria alternata.

The tangerine pathotype of A. alternata, which produces a unique host-selective ACT toxin causes brown spots on citrus leaves and fruits. In this study, we report a methionine biosynthesis regulator (MetR), which belong to bZIP transcription factor, is required for methionine metabolism, oxidative stress tolerance and pathogenicity. We generated two ΔAaMetR mutants in the tangerine pathotype of Alternaria alternata and investigated the resulting mutant phenotypes. The ΔAaMetR disruption mutant grew poorly in the absence of methionine and unable to produce conidia. Furthermore, pathogenicity tests have shown that ΔAaMetR mutant on their tangerine host can neither penetrate nor cause disease. These ΔAaMetR mutants exhibit an increased sensitivity to exogenous H₂O₂ and many ROS generating oxidants. To elucidate the transcription network of AaMetR, we performed RNA-Seq experiments on wild-type and ΔAaMetR mutant and identified genes that were differentially expressed between the two genotypes. Transcriptome data demonstrated that AaMetR contributes in many other biological processes including ROS detoxification, sulfur transfer, and amino acid metabolism. Comparative transcriptome analysis indicated that the ΔAaMetR mutant up-regulated several genes involved in cysteine and methionine metabolism. In conclusion, our results highlight the global regulatory role of AaMetR in cysteine and methionine metabolism and provide new insights into the crucial role of ROS detoxification, sporulation and pathogenicity in the tangerine pathotype of A. alternata.