AUTHOR=Wang Mingshuang , Yang Xiao , Ruan Ruoxin , Fu Huilan , Li Hongye 

TITLE=Csn5 Is Required for the Conidiogenesis and Pathogenesis of the Alternaria alternata Tangerine Pathotype

JOURNAL=Frontiers in Microbiology

VOLUME=9

YEAR=2018

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2018.00508

DOI=10.3389/fmicb.2018.00508

ISSN=1664-302X

ABSTRACT=<p>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 of <italic>csn5</italic> in phytopathogenic fungi are poorly understood. Here, we knocked out the <italic>csn5</italic> ortholog (<italic>Aacsn5</italic>) in the tangerine pathotype of <italic>Alternaria alternata</italic>. The Δ<italic>Aacsn5</italic> mutant showed a moderately reduced growth rate compared to the wildtype strain and was unable to produce conidia. The growth of Δ<italic>Aacsn5</italic> mutant was not affected in response to oxidative and osmotic stresses. Virulence assays revealed that Δ<italic>Aacsn5</italic> induced no or significantly reduced necrotic lesions on detached citrus leaves. The defects in hyphal growth, conidial sporulation, and pathogenicity of Δ<italic>Aacsn5</italic> were restored by genetic complementation of the mutant with wildtype <italic>Aacsn5</italic>. To explore the molecular mechanisms of conidiation and pathogenesis underlying <italic>Aacsn5</italic> regulation, we systematically examined the transcriptomes of both Δ<italic>Aacsn5</italic> and the wildtype. Generally, 881 genes were overexpressed and 777 were underexpressed in the Δ<italic>Aacsn5</italic> mutant 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 of <italic>csn1–4</italic> and <italic>csn7</italic> in Δ<italic>Aacsn5</italic> was 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 of <italic>csn5</italic> on conidiation and pathogenicity in plant pathogenic fungi and provide a foundation for future investigations.</p>