SNARE genes CcSec22 and CcSso1 coordinate fungal growth, sporulation, cell wall stress tolerance, endocytosis and full virulence in Cytospora chrysosperma.

Soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) facilitate intracellular vesicle trafficking and membrane fusion in eukaryotic organisms, significantly influencing fungal growth, development, and pathogenicity. Despite their importance, the specific functions of individual SNARE subunits remain largely unexplored. In Cytospora chrysosperma, a pathogen causing substantial damage to woody plants and leading to considerable ecological and economic impacts, 22 SNAREs have been identified. Yet, their functional roles have not been previously characterized. In this study, we focused on two SNARE-encoding genes, CcSec22 and CcSso1 that are supposed to mediate endoplasmic reticulum (ER)-Golgi and trans-Golgi Network (TGN)-secretory vesicle transport respectively. Notably, both genes demonstrate significantly elevated expression during the infection process. Targeted deletion of either of them resulted in retarded mycelial growth and remarkably decreased tolerance towards different cell-wall stressors. Interestingly, CcSec22 deletion mutants formed more hyphal branches while CcSso1 was required for morphological maintenance of conidiospores. More importantly, lack of either of them significantly reduced hyphal endocytosis and fungal virulence on host poplar. Collectively, our data highlighted that the SNARE genes CcSec22 and CcSso1 play pleiotropic roles in mycelial growth and development, stress responses, conidiation, endocytosis and in particular, they are required for the full virulence of C. chrysosperma. This study provides an insight into the role of SNARE proteins in C. chrysosperma pathogenesis.