The catalytic subunit of cAMP-dependent protein kinase A StPKA-c contributes to conidiation and early invasion in the phytopathogenic fungus Setosphaeria turcica.

Cyclic adenosine monophosphate (cAMP)-dependent protein kinase A (PKA) is an important mediator of signal transduction in eukaryotic cells. Thus, identifying its function is necessary to understand the cAMP signaling network. StPKA-c, the PKA catalytic subunit gene in Setosphaeria turcica, was investigated by RNA interference technology. Transformant strains M3, M5, and M9 with diverse StPKA-c silencing efficiency were confirmed by reverse transcription polymerase chain reaction and Northern blot. Compared with the wild-type strain 01-23, the transformant strains exhibited increased growth rate and significantly decreased conidium production. In addition, the ratios of spore germination and appressorium formation and penetration were slightly reduced. Relative to the wild-type strain, the transformants demonstrated different colony color, greatly reduced pathogenicity, and similar HT-toxin activity. Further studies showed that the content of intracellular melanin in the transformants significantly decreased, and the transcription of transcriptional factor StMR was down-regulated correspondingly. The transcription and enzyme activity of xylanase was also impaired. Thus, we proposed that StPKA-c was mainly involved in the mycelium growth, conidiation, and pathogenesis of S. turcica. Furthermore, it was positively correlated with the biosyntheses of melanin and xylanase but dispensable for the activity of HT-toxin.