Functional dissection of Gα subunits in Ustilago esculenta: Uegpa3 governs cAMP-PKA-dependent dimorphism and virulence to Zizania latifolia.

Ustilago esculenta is a dimorphic endophytic fungus that specifically infects Zizania latifolia, inducing stem swelling to form the economically important aquatic vegetable "Jiaobai". The pathogenicity of U. esculenta is closely associated with its dimorphic switch. This study systematically characterized the four G protein α subunit genes (Uegpa1-Uegpa4) in U. esculenta. Functional analysis revealed that Uegpa3 plays an indispensable role in pathogenicity by regulating dimorphic transition via the cAMP-PKA signaling pathway. Deletion of Uegpa3 resulted in defective conjugation tube formation, impaired mating, and loss of infectivity, all of which were restored upon exogenous cAMP supplementation. In contrast, deletion of Uegpa2 or Uegpa4 resulted in no observable phenotypic alterations. This study provides the first systematic functional characterization of Gα subunits in U. esculenta, and specifically reveals the crucial role of Uegpa3 in regulating dimorphic transition and pathogenicity through the cAMP-PKA pathway. These findings offer new insights into the mechanisms underlying the interaction between U. esculenta and its host Z. latifolia.