Mingshuang Wang, Xiao Yang, Ruoxin Ruan, Huilan Fu, Hongye Li
Abstract
The COP9 signalosome (CSN) is a highly conserved protein complex involved in the ubiquitin-proteasome system. Its metalloisopeptidase activity resides in subunit 5 (CSN5). Functions ofcsn5in phytopathogenic fungi are poorly understood. Here, we knocked out thecsn5ortholog (Aacsn5) in the tangerine pathotype ofAlternaria alternata. The ΔAacsn5mutant showed a moderately reduced growth rate compared to the wildtype strain and was unable to produce conidia. The growth of ΔAacsn5mutant was not affected in response to oxidative and osmotic stresses. Virulence assays revealed that ΔAacsn5induced no or significantly reduced necrotic lesions on detached citrus leaves. The defects in hyphal growth, conidial sporulation, and pathogenicity of ΔAacsn5were restored by genetic complementation of the mutant with wildtypeAacsn5. To explore the molecular mechanisms of conidiation and pathogenesis underlyingAacsn5regulation, we systematically examined the transcriptomes of both ΔAacsn5and the wildtype. Generally, 881 genes were overexpressed and 777 were underexpressed in the ΔAacsn5mutant during conidiation while 694 overexpressed and 993 underexpressed during infection. During asexual development, genes related to the transport processes and nitrogen metabolism were significantly downregulated; the expression ofcsn1-4andcsn7in ΔAacsn5was significantly elevated; secondary metabolism gene clusters were broadly affected; especially, the transcript level of the whole of cluster 28 and 30 was strongly induced. During infection, the expression of the host-specific ACT toxin gene cluster which controls the biosynthesis of the citrus specific toxin was significantly repressed; many other SM clusters with unknown products were also regulated; 86 out of 373 carbohydrate-active enzymes responsible for breaking down the plant dead tissues showed uniquely decreased expression. Taken together, our results expand our understanding of the roles ofcsn5on conidiation and pathogenicity in plant pathogenic fungi and provide a foundation for future investigations.
