Abstract
In the chlorophyll biosynthesis pathway, the 8-vinyl group of the chlorophyll precursor is reduced to an ethyl group by 8-vinyl reductase. Two isozymes of 8-vinyl reductase have been described in oxygenic photosynthetic organisms: one encoded by BciA and another by BciB. Only BciB contains an [Fe-S] cluster and most cyanobacteria harbor this form; whereas a few contain BciA. Given this disparity in distribution, cyanobacterial BciA has remained largely overlooked, which has limited understanding of chlorophyll biosynthesis in these microorganisms. Here, we reveal that cyanobacterial BciA encodes a functional 8-vinyl reductase, as evidenced by measuring the in vitro activity of recombinant Synechococcus and Acaryochloris BciA. Genomic comparison revealed that BciB had been replaced by BciA during evolution of the marine cyanobacterium Synechococcus, and coincided with replacement of Fe-superoxide dismutase (SOD) with Ni-SOD. These findings imply that the acquisition of BciA confers an adaptive advantage to cyanobacteria living in low-iron oceanic environments.
Highlights
Almost all the energy that sustains life on Earth is produced through photosynthesis
This study provides a better understanding of the enzymatic diversity supporting chlorophyll biosynthesis in cyanobacteria
After incubation of 8V chlorophyllide with these recombinant proteins, a chlorophyllide with an ethyl group at position 8 was detected (Fig. 2). These results confirm that BciA from marine cyanobacteria encodes 8V reductase
Summary
Almost all the energy that sustains life on Earth is produced through photosynthesis. Chlorophyll is a pigment that captures light energy. In addition to chlorophyll a, green algae, plants, and some cyanobacteria possess chlorophyll b (Fig. 1). In plants, both chlorophylls are degraded enzymatically (Kuai et al 2018). The first step in chlorophyll a degradation is the extraction of the central magnesium atom by Mg-dechelatase, which is encoded by Stay-Green, to form pheophytin a. To the best of our knowledge, Mg-dechelatase or pheophorbide a oxygenase have not been identified in cyanobacteria, and it remains unclear whether chlorophyll is degraded to smaller molecules within cyanobacterial cells
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
