Aabrm1-mediated melanin synthesis is essential to growth and development, stress adaption, and pathogenicity in Alternaria alternata

Scytalone dehydratase (brm1) is one of the key enzymes in 1, 8-dihydroxynaphthalene (DHN) melanin synthesis, which mediates melanin biosythesis and regulates cell biological process of plant fungi, but its function in Alternaria alternata , the causal agent of pear black spot, is unclear. Brm1 in A. alternata was cloned, identified, and named as Aabrm1 . An Aabrm1 -deletion mutant was generated and revealed that the deletion of Aabrm1 leads to a significant decrease in melanin production and forms orange colony smooth spores. In addition, the deletion of Aabrm1 gene impaired infection structure information and penetration. The external stress resistance of Δ Aabrm1 was significantly weakened, and, in particular, it is very sensitive to oxidative stress, and the contents of H 2 O 2 and O 2 .- in Δ Aabrm1 were significantly increased. Virulence of Δ Aabrm1 was reduced in non-wound-inoculated pear leaves but not changed in wound-inoculated pear fruit. These results indicated that Aabrm1- mediated melanin synthesis plays an important role in the pathogenicity of A. alternata.