Transcriptional and Developmental Responses by Anabaena to Deprivation of Fixed Nitrogen
Xudong Xu, Jeff Elhai, and C. Peter Wolk
from: The Cyanobacteria: Molecular Biology, Genomics and Evolution (Edited by: Antonia Herrero and Enrique Flores). Caister Academic Press, U.K. (2008)
Deprivation of fixed nitrogen, to which the formation of dinitrogen-fixing cells called heterocysts is a conspicuous response, appears to initiate a switch from reliance on photosynthesis for ATP, reductant, and carbon to reliance-in developing cells-on endogenous glycogen stores, heightened utilization of the oxidative pentose phosphate pathway, and-at least in mature heterocysts-photosystem I and influx from vegetative cells. Sugars are needed to produce heterocyst envelope layers of polysaccharide and glycolipid. Decreased transcription and translation of a few highly expressed genes may make possible the increased transcription and translation of many others. Although we interpret metabolic capabilities from microarray data, we stress the hazards of doing so, and emphasize that the interpretations remain to be evaluated. Little is known of the regulation of gene expression during heterocyst differentiation. NtcA is required for the expression of nrrA and many other genes, NrrA is required for the full induction of hetR, and HetR is required for the expression of many downstream genes. Numerous regulatory-family genes are significantly induced during heterocyst differentiation and may importantly regulate the process. Some genes of unknown function increase many-fold in expression during differentiation, leading one to wonder what their roles may be read more ...