Abstract: The sucrose non-fermenting 1（SNF1）protein kinase complex is a highly conserved heterotrimeric protein，including a catalytic subunit α and two regulatory subunits（β，γ），which plays an important role in fungal development and virulence. Our previous study revealed that catalytic subunit α of the tangerine pathotype of Alternaria alternata plays a crucial part in the utilization of alternative carbon sources and virulence. In order to determine the functions of other subunits of the SNF1 complex in the tangerine pathotype of A. alternata，we studied the protein sequence of the tangerine pathotype of A. alternata strain Z7 and identified one β subunit（AaSIP2）. The biological functions of AaSIP2 were characterized using gene knock-out and complementation strategy. The results showed that the mutants had less conidia and slower spore germination，more sensitive to sugar and partial salt stress compared with the wild type and complementary strain. The vegetative growth of the ΔAaSip2 mutants were reduced in MM medium with different single carbon sources. Additionally，virulence assays revealed that ΔAaSip2 induced significantly reduced necrotic lesions on detached citrus leaves. In conclution，we reveal that AaSIP2 is required for utilization of carbon source，conidiation，spore germination，stress response and virulence in A. alternata.

Key words: citrus, tangerine pathotype of Alternaria alternata, AaSIP2, utilization of carbon source；virulence