Carotenoid Biosynthesis in Cyanobacteria: Structural and Evolutionary Scenarios Based on Comparative Genomics
Liang C, Zhao F, Wei W, Wen Z, Qin S. Carotenoid Biosynthesis in Cyanobacteria
Key Laboratory of Experimental Marine Biology, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China
Graduate University, Chinese Academy of Sciences, Beijing 100039, China.
The recent access to the overwhelming amount genomic data of cyanobacteria has given birth to a novel approach called comparative genomics. The putative enzymes involved in the carotenoid biosynthesis among the cyanobacteria were determined by similarity-based tools. The reconstruction of biosynthetic pathway was based on the related enzymes. It is interesting to find that nearly all the cyanobacteria share quite similar pathway to synthesize β-carotene except for Gloeobacter violaceus PCC 7421. The enzymes, crtE-B-P-Qb-L, involved in the upstream pathway are more conserved than the subsequent ones (crtW-R). In addition, many carotenoid synthesis enzymes exhibit diversity in structure and function. Such examples in the families of ζ –carotene desaturase, lycopene cylases and carotene ketolases were described in this article. When we mapped these crt genes to the cyanobacterial genomes, the crt genes showed great structural variation among species. All of them are dispersed on the whole chromosome in contrast to the linear adjacent distribution of the crt gene cluster in other eubacteria. Moreover, in unicellular cyanobacteria, each step of the carotenogenic pathway is usually catalyzed by one gene product, whereas multiple ketolase genes are found in filamentous cyanobacteria. Such increased numbers of crt genes and their correlation to the ecological adaptation were carefully discussed.
Keywords: Cyanobacteria, Comparative genomics, Carotenoid pathway
Int J Biol Sci 2006; 2:197-207 ©Ivyspring International Publisher