P s H int1, associated with the G ‐protein α subunit PsGPA1 , is required for the chemotaxis and pathogenicity of P hytophthora sojae

Summary Zoospore chemotaxis to soybean isoflavones is essential in the early stages of infection by the oomycete pathogen P hytophthora sojae . Previously, we have identified a G ‐protein α subunit encoded by PsGPA1 which regulates the chemotaxis and pathogenicity of P . sojae . In the present study, we used affinity purification to identify PsGPA1 ‐interacting proteins, including P s H int1, a histidine triad ( HIT ) domain‐containing protein orthologous to human HIT nucleotide‐binding protein 1 ( HINT1 ). P s H int1 interacted with both the guanosine triphosphate ( GTP )‐ and guanosine diphosphate ( GDP )‐bound forms of PsGPA1 . An analysis of the gene‐silenced transformants revealed that P s H int1 was involved in the chemotropic response of zoospores to the isoflavone daidzein. During interaction with a susceptible soybean cultivar, P s H int1 ‐silenced transformants displayed significantly reduced infectious hyphal extension and caused a strong cell death in plants. In addition, the transformants displayed defective cyst germination, forming abnormal germ tubes that were highly branched and exhibited apical swelling. These results suggest that P s H int1 not only regulates chemotaxis by interacting with PsGPA1 , but also participates in a G α‐independent pathway involved in the pathogenicity of P . sojae .