Regulator of G-Protein Signalling Protein AaRgs2 Negatively Regulates Appressorium-Like Formation of Alternaria alternata Induced by Pear Cutin Monomer via the AaRgs2-AaGα1-AaAC Module.

Pathogenic fungi have developed complex and specific infection strategies to invade host tissues successfully. Regulator of G-protein signalling (RGS) proteins exhibit GTPase-accelerating protein activities and play a crucial role in the formation of infection structures in pathogenic fungi. However, specific regulatory mechanisms remain unclear. In the present study, observations of infection structure indicated that the deletion of AaRgs2 resulted in a significant increase in spore germination. Appressorium-like formation rate was compared to that of the wild-type strain on a Gelbond hydrophobic membrane coated with 16-hydroxyhexadecanoic acid or 1,16-hexadecanediol, which are cutin monomers in pear peel. Transcriptome analysis during the appressorium-like formation stage revealed 4124 differentially expressed genes (DEGs) that were annotated in the wild-type strain and the ΔAaRgs2 mutant. KEGG enrichment analysis showed that the cAMP-PKA signalling pathway, MAPK signalling pathway, peroxisome and autophagy pathway were closely associated with appressorium-like formation regulated by AaRgs2. Yeast two-hybrid and bimolecular fluorescence complementation assays demonstrated a specific physical interaction between AaRgs2 and AaGα1, further confirming that AaGα1 interacted with the Pfam domain of adenylate cyclase AC. Our studies provide evidence suggesting that AaRgs2 negatively regulates appressorium-like formation of A. alternata induced by pear cutin monomer via the AaRgs2-AaGα1-AaAC module.