UV/blue light photoreceptors involved in photomovement of cyanobacterium Synechocystis sp. PCC 6803

Abstract

Photomovement in cyanobacteria is a complex interplay between perception of the directional light of various wavelengths, growth characteristics and external environment conditions. Synechocystis sp. PCC 6803 (hereafter Syn6803) has become the model system to study light signal transduction in cyanobacteria and several important players including photoreceptors and other partners have been identified recently. Multiple photoreceptors such as phytochrome-like proteins, BLUF proteins, and signal transduction pathways are involved in cyanobacterial photomovement. However, the dissection of these interacting pathways has not been accomplished yet. Despite considerable advances that were made during the past decades in the field of phytochrome, the mechanisms and photoreceptors that mediate UV/blue light reception have also remained largely unidentified. The work presented in this thesis can provide a clue to identify the UV/blue photoreceptors and the requisite signaling mechanisms. To elucidate the role of pterin in UV/blue light signal transduction of Syn6803, we analyzed the effects of inactivating the pteridine glycosyltransferase gene (pgtA) on the photomovement of the cyanobacterium Syn6803 under different light conditions. The pgtA mutant displayed abnormal photomovement under UV-A/blue light. Especially, the pgtA mutant showed a negative phototactic response under UV-A (315-400 nm), whereas wild-type did not show any photomovement. Inhibition of pterin biosynthesis by N-acetylserotonin (NAS), an inhibitor of sepiapterin reductase, also inhibited a positive phototactic response of wild-type under white and blue light. In addition, negative phototaxis of the pgtA mutant was observed under UV-A/blue light in the presence of NAS. These results indicated that the product of the PgtA enzyme, cyanopterin, is involved in the inhibition of the negative phototaxis of wild-type by sensing the UV-A. However, 2,4-diamino-6-hydroxypyrimidine-mediated inhibition of GTP ...