4.7 Article

Aaprb1, a subtilsin-like protease, required for autophagy and virulence of the tangerine pathotype of Alternaria alternata

Journal

MICROBIOLOGICAL RESEARCH
Volume 240, Issue -, Pages -

Publisher

ELSEVIER GMBH
DOI: 10.1016/j.micres.2020.126537

Keywords

Alternaria alternata; Subtilisin-like serine protease; Autophagy; Virulence; Aaprb1

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Funding

  1. National Natural Science Foundation of China [31571948]
  2. earmarked fund for China Agriculture Research System [CARS-26]

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Subtilisin-like serine protease secreted by pathogenic fungi can facilitate the infection and acquisition of nutrients. Functions of subtilisin-like serine proteases in the phytopathogenic fungus Alternaria alternata remains unknown. In the current study, 15 subtilisin-like serine proteases were individually deleted in the citrus fungal pathogen A. alternata. Only one, designated AaPrb1, was found to be required for A. alternata pathogenesis. The AaPrb1 deficiency strain (Delta Aaprb1) reduced growth, conidiation, the formation of aerial hyphae, protease production, and virulence on citrus leaves. However, biochemical analyses and bioassays revealed that Delta Aaprb1 plays no role in the production of ACT toxin. Through Y2H assays, Aaprb1 was found to interact with Aapep4, a vacuole-localized proteinase A in A. alternata. Furthermore, silencing AaPep4 in A. alternata resulted in phenotypes similar with those of Delta Aaprb1. Expression of AaPrb1 was found to be regulated by AaPep4. TEM showed that AaPrb1 and AaPep4 were involved in the suppression of the degradation of autophagosomes. Deletion of the autophagy gene AaAtg8 in A. alternata decreased conidiation, the formation of aerial hyphae and pathogenicity similar to Delta Aaprb1, implying that some phenotypes of Delta Aaprb1 were due to the impairment of autophagy. Overall, this study expands our understanding of how A. alternata utilizes the subtilisin-like serine protease to achieve successful infection in the plant host.

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