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The relevance of pilus-related genes to motility, pilus structure on the cell surface and competency of natural transformation was studied by gene disruption analysis in the unicellular motile cyanobacterium Synechocystis: sp. PCC 6803. The genes disrupted in this study were chosen as related to the pil genes for biogenesis of the type IV pili in a Gram-negative bacterium Pseudomonas aeruginosa. It was found that motility of Synechocystis cells was lost in the mutants of slr0063, slr1274, slr1275, slr1276, slr1277 and sll1694 together with a simultaneous loss of the thick pili on the cell surface. Competency of the natural transformation was lost in the mutants listed above and slr0197-disruptant. The gene slr0197 was previously predicted as a competence gene by a search with sequence-independent DNA-binding structure [Yura et al. (1999) DNA Res. 6: 75]. It was suggested that both DNA uptake for natural transformation and motility are mediated by a specific type IV-like pilus structure, while a putative DNA-binding protein encoded by slr0197 is additionally required for the DNA uptake. Based on the homology with the pil genes in P: aeruginosa, slr0063, slr1274, slr1275, slr1276, slr1277 and sll1694 were designated pilB1, pilM, pilN, pilO, pilQ and pilA1, respectively. The gene slr0197 was designated comA.

Gametophytes of Ceratopteris richardii developed into strap-shaped prothalli in the dark. The prothalli had an apical meristem, a subapical elongation zone and a basal zone where no growth occurred. Continuous irradiation of blue light inhibited cell growth of the elongation zone, although red or far-red light had no effect on elongation. Cortical microtubules (MTs) of subapical cells reoriented from transverse to oblique or parallel to the growing axis during blue light inhibition. Each region of the strap-shaped prothallus was irradiated with a micro-beam of blue light. Cell elongation in the subapical region was not inhibited by irradiation at the apical meristem. Irradiation of the subapical region inhibited cell elongation to a similar extent as the whole irradiation control. When a single elongating cell at one side of the subapical region was irradiated by a blue microbeam, elongation was inhibited in a cell at the irradiate side only, resulting in a bowing prothallus. Cortical MTs reoriented from transverse to longitudinal to the cell axis in irradiated cells only. The results indicate that each cell in the subapical region perceives blue light by itself, reorients only its cortical MTs and ceases only its cell elongation, independent of surrounding cells.