The Gα subunit gene SsGpa1 regulates virulence and mycovirus horizontal transmission in Sclerotinia sclerotiorum

Abstract Fungal vegetative incompatibility (VIC) usually inhibits the horizontal transmission of mycoviruses. Our previous work demonstrated that Sclerotinia sclerotiorum mycoreovirus 4 (SsMYRV4), a hypovirulence-associated mycovirus, suppresses VIC to facilitate horizontal transmission of heterologous mycoviruses in Sclerotinia sclerotiorum, while downregulating heterotrimeric G protein genes. However, the biological function of these genes in mycovirus horizontal transmission and mycovirus-mediated hypovirulence remains poorly understood. To address this knowledge gap, we generated targeted gene deletion mutants of the Gα subunit gene (SsGpa1) in S. sclerotiorum. SsGpa1 deletion mutants displayed reduced hyphal growth, increased abiotic stress sensitivity, defective sclerotia formation, and attenuated virulence on rapeseed. Moreover, SsGpa1 deletion partially impairs the death barrage formation during the vegetative incompatibility response, promoting mycovirus horizontal transmission between incompatible S. sclerotiorum strains. Comparative transcriptomic analysis between ΔSsGpa1 and its parental strain Ep-1PNA367 during dual-culture of VIC strains revealed that apoptosis- and autophagy-related genes and ROS generation and scavenging genes act as potential downstream effectors of the SsGpa1 signaling pathway. Together, the regulatory role of SsGpa1 in VIC response unveils novel molecular targets for biocontrol strategies by manipulating mycovirus transmission in phytopathogenic fungi.