Transcription factor AacmrA mediated melanin synthesis regulates the growth, appressorium formation, stress response and pathogenicity of pear fungal Alternaria alternata

CmrA, as transcription factor for regulating DHN-melanin synthesis, controls melanin synthesis gene expression of pksA , brm1 and brm2 , and also regulate growth, development, stress response and virulence of plant fungi. However, little is known about the roles of CmrA on infection structure formation, penetration and pathogenicity of Alternaria alternata, the causal agent of pear black spot. Here, we identified c mrA gene in A. alternata and assigned as AacmrA , sequence alignment and phylogenetic analysis revealed that AacmrA is highly conserved among fungi and encoded protein contain two Cys2His2 zinc finger motifs and one Zn(II)2Cys6 zinc cluster protein motif. ΔAacmrA severely decreased melanin production and DHN melanin synthesis related genes expression. Deletion of AacmrA impaired the morphology of spore and hyphae. Spore germination and appressorium formation induced by hydrophobicity surfaces and fruit wax significantly decreased in Δ AacmrA mutant. Δ AacmrA mutants were more sensitive than the wild type to osmotic stress and cell wall inhibitors, especially more sensitive to oxidative stress. In addition, lesion diameter of pear fruit wound inoculated with the Δ AacmrA mutant was reduced by 40.8% compared with the wild type 12 d after inoculation. All findings of this study suggested that AacmrA is required for melanin biosynthesis, infection structure formation, and pathogenicity in A. alternata .