The Interaction Mechanism Study Between Two-Component Signal Transduction Systems And Serine/Thronine Kinase Systems In Synechocystis Sp. PCC6803under Specific Stress Conditions

Cyanobacteria have developed various response mechanisms in long evolution to sense and adapt to external or internal changes under abiotic stresses. The signal transduction system of a model cyanobacterium Synechocystis sp. PCC6803includes mainly two-component signal transduction systems of eukaryotic-type serine/threonine kinases (STKs), on which most have been investigated at present. These two-component systems play a major role in regulating cell activities in cyanobacteria. At home and abroad, functional study was now mainly on one signal two-component transduction system, while there were limited fuctional study on STKs system in cyanobacteria. The experiment confirmed that SpkG in Synechocystis sp. PCC6803was indicated to be involved in response to high-salt stress. And it is for the first time to found that a STK and two-component signal transduction system work together in the high-salt mediated signal transduction process. However, the detailed information on how they cooperate and interact each other is still mysterious. For example, how these two system kinases transfer signals to downstream proteins, and especially, could these kinases regulate gene expression directly, remain unknown.In order to address the issues above mentioned, we will perform this project based on the sequenced Synechocystis genome. Herein, the model cyanobacterial species Synechocystis sp. PCC68O3was chosen as a study material, in which STK and two-component systems were investigated under low-temperature (LT) and nitrogen deficiency (ND) stress by mutant. Real Time RT-PCR, and DNA microarray analysis, respectively. We have found that the serine/threonine kinase SpkE is not only participate in the signal transduction induced by LT and ND stresses, but also work together with the histidine kinase Hik34to respond to changes under ND stress. And spkE maybe regulated by the histidine kinase Hik34under ND condition. Moreover, it was also found that the serine/threonine kinase SpkG and histidine kinase Hik33were together involved in ND-inducible signal transduction, and was likely that SpkG regulated hik33gene negatively.There were three points demonstrated by our experimental studies. First of all, SpkE showing no protein kinase activities, which may be related to nitrogen metabolism, was indicated to be involved in LT-and ND-inducible signal transduction. Perhaps spkE was regulated by the histidine kinase Hik34under ND condition. Secondly, there are two pairs of interacting kinases in two signal transduction pathways could be both activated by certain environmental factors. At the same time, the same pair of interacting kinases could both act on responding to changes under different abiotic stresses. Lastly, we found that there were interactions between three serine/threonine kinases and two histidine kinases, and the similar phenomenon occurred between two serine/threonine kinases. It initially revealed the interaction mechanism in between the two signal transduction systems, which provided a fundation for outlining detailed regulatory network for stress resistance in cyanobacteria. In addition, cyanobacteria possess the features of both bacteria and plant, which can be transformed naturally and could be a useful reference to study signal transduction system in higher plants.