Signal Transduction Involved In Heterocyst Development In Anabaena PCC7120

Anabaena PCC 7120 is a filamentous cyanobacterium capable of both photosynthesis and dinitrogen fixation under aerobic conditions. Under conditions of combined nitrogen depletion, 5-10% of the cells along each fillament are induced to become specialized ones, called heterocysts, that are capable of molecular nitrogen fixation. Heterocyst create a microoxic environment to protect nitrogenase from oxygen. Up to now , the mechanism of singnal transduction involved in heterocyst differentiation is still unclear. The main objective of this study was to analyse genes of singnal transduction involved in heterocyst differentiation.Genome sequences of Anabaena PCC 7120 are available at the CyanoBase databank. Based on the genomic data, 211 genes encoding two-component signaling elements have been retrieved. There are 131 genes encoding histine kinase and 80 genes encoding response regulator, that are classified into 7 and 6 subfamilies respectively. Many proteins in Anabaena PCC 7120 have incorporated both modules of two-component systems and catalytic domains of either Ser/Thr kinases or phosphatases. A subfamily of 13 genes encode proteins with both a Ser/Thr kinase domain anti a His kinase domain, and another four genes were also found whose products have both a response regulator domain and a Ser/Thr phosphatase domain. Of all the signaling proteins in Anabaena PCC 7120, about one third (35%) are conserved in the genome of the unicellular cyanobacterium strain Synechocystis PCC 6803. Interestingly, one subfamily of His kinases and two subfamilies of response regulators are present in Anabaena PCC 7120, but absent in Synechocystis PCC 6803.109 genes were inactivated by insertion of a cassete confering antibiotic resistance. 19 single and 74 double recombinants were obtained. These mutants were examined for phenotypes after nitrogen depletion .The result showed that one mutant was unable to differentiate heterocyst, three formed heterocysts but still could not maintain normal growth, four growed slowly with heterocyst differentiation. These genes may play roles in hetetocyst differentiation or function.The gene chip used in this study contained 407 genes. The genes expression profil responding to nitrogen deprivation was analyzed using this gene-chip.The results indicated that 28 of 407 genes had an altered pattern of expression 24 hours after nitrogen deprivation. These studies provide a genetic and molecular basis for the understranding of the signaling network underlying heterocyst development in caynobacteria.