Role of in Filamentous Growth and Pathogenicity of .

is a dimorphic fungus that specifically infects , causing stem swelling and the formation of an edible fleshy stem known as jiaobai. The pathogenicity of is closely associated with the development of jiaobai and phenotypic differentiation. Msb2 acts as a key upstream sensor in the MAPK (mitogen-activated protein kinase) signaling pathway, playing critical roles in fungal hyphal growth, osmotic regulation, maintenance of cell wall integrity, temperature adaptation, and pathogenicity. In this study, we cloned the gene from (GenBank No. MW768949). The open reading frame of is 3015 bp in length, lacks introns, encodes a 1004-amino-acid protein with a conserved serine-rich domain, and is localized to the vacuole. Expression analysis revealed that is inducibly expressed during both hyphal growth and infection processes. Deletion of did not affect haploid morphology or growth rate in vitro but significantly impaired the strain's mating ability, suppressed filamentous growth, slowed host infection progression, and downregulated the expression of signaling pathway genes associated with pathogenicity. Notably, the deletion of did not influence the in vitro growth of under hyperosmotic, thermal, or oxidative stress conditions. These findings underscore the critical role of in regulating the pathogenicity of . This study provides insights into the interaction between and , particularly the mechanisms that drive host stem swelling.