AaRgs1 and AaRgs2 differential regulate fungal development, stress response and appressorium-like formation in Alternaria alternata

Alternaria alternata can recognize and respond to physichemical cues from the host plant epidermis through a complex signaling network to initiate infectious structures formation. The primarily functions of RGS as a negative regulator of G protein signaling has been characterized in several model fungi, but its biological function in A. alternata remains unclear. In present study three RGS proteins were identified in A. alternata by Blast alignment and designed as AaRgs1, AaRgs2 and AaRgs3. Targeted genes deletion demonstrated that AaRgs1 and AaRgs2 play the opposite function in vegetative growth, melanin production and secretion, stress response and appressorium-like formation rate in A. alternata, while AaRgs3 had no certain regulatory effect. Differently, AaRgs1 negatively regulated tolerance to high-osmosis stress response and cell wall synthesis inhibitors by down regulating the expression level of AaHog1 and AaSlt2. AaRgs2 acts as a negative role in regulating appressorium-like formation rates through decreasing intracellular cyclic adenosine monophosphate (cAMP) accumulation. Deletion of AaRgs1 and AaRgs2 also resulted in significantly reducing penetrating ability and pathogenicity. The findings indicated that RGS proteins play multiple roles in fungal development, stress response and appressorium-like formation of A. alternata.