Photoregulation of pigmentation during complementary chromatic acclimation (CCA) is well studied inFremyella diplosiphon; however, mechanistic insights into the CCA-associated morphological changes are still emerging.F. diplosiphoncells are rectangular under green light (GL), whereas cells are smaller and spherical under red light (RL). Here, we investigate the role of morphogenesbolAandmreBduring CCA using gene expression and gene function analyses. TheF.diplosiphonbolAgene is essential as its complete removal from the genome was unsuccessful. Depletion ofbolAresulted in slow growth, morphological defects and the accumulation of high levels of reactive oxygen species in a partially segregated ΔbolAstrain. Higher expression ofbolAwas observed under RL and was correlated with lower expression ofmreBandmreCgenes in wild type. In a ΔrcaEstrain that lacks the red-/green-responsive RcaE photoreceptor, the expression ofbolAandmregenes was altered under both RL and GL. Observed gene expression relationships suggest thatmreBandmreCexpression is controlled by RcaE-dependent photoregulation ofbolAexpression. Expression ofF. diplosiphonbolAandmreBhomologues inEscherichia colidemonstrated functional conservation of the encoded proteins. Together, these studies establish roles forbolAandmreBin RcaE-dependent regulation of cellular morphology.