Impaired cell-cell communication in multicellular cyanobacteria affects carbon uptake, photosynthesis and the cell wall

Cell-cell communication is an essential attribute of multicellular organisms. We studied the effects of perturbed communication in multicellular filaments of mutant derivatives of the heterocyst-forming cyanobacterium Anabaena sp. strain PCC 7120, in which septal proteins were deleted. Filaments of sepJ and sepJ/fraC/fraD deleted strains showed marked differences in growth, pigment absorption spectra and spatial patterns of expression of the hetR gene encoding a master regulator of heterocyst differentiation. To understand the global changes in gene expression that take place as a result of impaired cell-cell molecular transfer, we mapped the transcriptional landscape of wild-type and mutant filaments using RNA-seq, both under nitrogen-replete and nitrogen-poor conditions. Our results show that the effects of sepJ and fraC/fraD deletions are not additive, and that far from affecting only passive transport between cells, perturbations to cell-cell communication in this model organism lead to significant changes in gene expression. Most significant effects include increased expression of genes encoding carbon uptake systems and some components of the photosynthetic apparatus, and decreased expression of genes encoding cell wall components related to heterocyst differentiation and to polysaccharide export. Thus, impairment of intercellular communication strongly affects specific aspects, notably related to carbon metabolism, of the biology of Anabaena. Anabaena PCC 7120 mRNA profiles of 18 hrs. nitrogen-replete and nitrogen-poor conditions, of Wild type (WT), sepJ deleted strain (CSVM34) and sepJ/fraC/fraD deleted strain(TM, CSVM141)