Eukaryote-like Ser/Thr protein kinase PrkA modulates sporulation via regulating the transcriptional factor σk in Bacillus subtilis

Protein kinase A (PrkA), also known as AMP-activated protein kinase, functions as a serine/threonine protein kinase (STPK), has been shown to be involved in a variety of important biologic processes, including pathogenesis of many important diseases in mammals. However, the biological functions of PrkA are less known in prokaryote cells. Here, we explored the function of PrkA as well as its underlying molecular mechanisms using the model bacterium Bacillus subtilis 168. When PrkA is inhibited by 9-beta-D-arabinofuranosyladenine (ara-A) in the wild type strain or deleted in the AprkA mutant strain, we observed sporulation defects in B. subtilis 168, suggesting that PrkA functions as a sporulation-related protein. Transcriptional analysis using the lacZ reporter gene demonstrated that deletion of prkA significantly reduced the expression of the transcriptional factor sigma(K) and its downstream genes. Complementation of sigK gene in prkA knockout mutant partially rescued the phenotype of Delta prkA, further supporting the hypothesis that the decreased sigma(K) expression should be one of the reasons for the sporulation defect resulting from prkA disruption. Finally, our data confirmed that Hpr (ScoC) negatively controlled the expression of transcriptional factor sigma(K), and thus PrkA accelerated sporulation and the expression of sigma(K) by suppression of Hpr (ScoC). Taken together, our study discovered a novel function of the eukaryotic-like STPK PrkA in spore development as well as its underlying molecular mechanism in B. subtilis.