Cyanobacterial hybrid kinase Sll0043 regulates phototaxis by suppressing pilin and twitching motility protein.

The unicellular cyanobacterium Synechocystis sp. PCC 6803 glides toward a light source through the interplay of positive phototaxis genes and proteins. In genetic analysis, the complete disruption of the hybrid sensory kinase sll0043 produced negative phototaxis. Furthermore, Sll0043 was found to be a hub protein by in silico prediction of protein-protein interaction, in which Sll0043 was predominantly linked to seven two-component proteins with high confidence. To understand the regulation and networking of positive phototaxis proteins, the proteomic profile of the sll0043 mutant was compared to that of wild-type. In the sll0043 mutant, 18 spots corresponding to 15 unique proteins were altered by 1.3 to 59 fold; the spots were identified by 2-DE/MALDI-MS analysis. Down-regulated proteins in the sll0043 null-mutant included chaperonins, superoxide dismutase, and phycocyanin beta-subunit. In contrast, nine proteins involved in photosynthesis, translation, regulatory function, and other functions were up-regulated. In particular, a twitching motility protein (PilT1) was induced over 2-fold in sll0043 mutant. Moreover, semi-quantitative and quantitative RT-PCR analysis revealed that pilin (pilA1), pili motor (pilT1), and pili switch gene (pilT2) were significantly increased in sll0043 mutant. These results suggest that the hybrid kinase Sll0043 regulates positive phototaxis by suppressing the expression of pili biosynthesis and regulatory genes and through the interplay with positive phototaxis/motility two-component proteins.