GSE36781
The transcription factor Amr1 induces melanin biosynthesis and suppresses virulence in Alternaria brassicicola
Alternaria brassicicola is a successful saprophyte and necrotrophic plant pathogen.  Several A. brassicicola genes have been characterized as virulence factors affecting pathogenesis of Brassica species.  To study regulatory mechanisms of pathogenesis, we mined 421 genes in silico encoding putative transcription factors in a machine-annotated, draft genome sequence of A. brassicicola.  Targeted gene disruption mutants for 114 of the genes with proteins predicted to contain at least one putative zinc-finger domain were produced and functionally analyzed.  Six of these genes were associated with pathogenesis.  Disruption mutants corresponding to five of the genes were =50% less virulent than the wild type. Unexpectedly, the mutants of one gene (designated Amr1) were 100% more virulent.  Amr1 is a homolog of Cmr1, a transcription factor previously found to regulate melanin biosynthesis in several fungi.  Gene deletion mutants (?amr1) were created and their phenotypes characterized.  The ?amr1 mutants utilized pectin as a carbon source more efficiently than the wild type, were melanin-deficient, and more sensitive to UV light and glucanase digestion.  The Amr1 protein was localized in the nuclei of hyphae and in highly melanized conidia during the late stage of plant pathogenesis.  RNA-seq analysis revealed that three genes in the melanin biosynthesis pathway, along with the deleted Amr1 gene, were not expressed in the mutants.  In contrast, many hydrolytic enzyme-coding genes were expressed at much higher levels in the mutants than in the wild type during pathogenesis.  The results of this study suggested that only a small number of transcription factors with zinc finger domains are needed to maintain strong virulence.  Furthermore, a gene important for survival in nature negatively affected virulence, probably by less efficient use of pectin.  We speculate that the functions of the Amr1 gene are important to the success of A. brassicicola as a competitive saprophyte and plant parasite Overall design: gene expression profile comparisons between wild type and a transcription factor mutant during the late stage of host infection