Carotenoid Biosynthetic Pathways Are Regulated by a Network of Multiple Cascades of Alternative Sigma Factors in Azospirillum brasilense Sp7

Abstract

Importance: Carotenoids play very important role in coping with photooxidative stress in prokaryotes and eukaryotes. Although extracytoplasmic function (ECF) sigma factors are known to directly regulate the expression of carotenoid biosynthetic genes in bacteria, regulation of carotenoid biosynthesis by cascade/s of sigma factors had not been reported. This study provides the first evidence of the involvement of multiple cascades of sigma factors in the regulation of carotenoid synthesis in any bacterium by showing the regulation of a gene encoding geranylgeranyl pyrophosphate synthase (crtE2) by RpoE1→RpoH2→CrtE2 and RpoE2→RpoH1→CrtE2 cascades in A. brasilense It also provides an insight in to existence of additional cascade/s regulating expression of another paralog of crtE.