Abstract
The orange carotenoid protein (OCP) family of proteins are light-activated proteins that function in dissipating excess energy absorbed by accessory light-harvesting complexes, i.e., phycobilisomes (PBSs), in cyanobacteria. Some cyanobacteria contain multiple homologs of the OCP-encoding gene (ocp). Fremyella diplosiphon, a cyanobacterium studied for light-dependent regulation of PBSs during complementary chromatic acclimation (CCA), contains several OCP homologs – two full-length OCPs, three Helical Carotenoid Proteins (HCPs) with homology to the N-terminus of OCP, and one C-terminal domain-like carotenoid protein (CCP) with homology to the C-terminus of OCP. We examined whether these homologs are distinctly regulated in response to different environmental factors, which could indicate distinct functions. We observed distinct patterns of expression for some OCP, HCP, and CCP encoding genes, and have evidence that light-dependent aspects of ocp homolog expression are regulated by photoreceptor RcaE which controls CCA. RcaE-dependent transcriptional regulator RcaC is also involved in the photoregulation of some hcp genes. Apart from light, additional environmental factors associated with cellular redox regulation impact the mRNA levels of ocp homologs, including salt, cold, and disruption of electron transport. Analyses of conserved sequences in the promoters of ocp homologs were conducted to gain additional insight into regulation of these genes. Several conserved regulatory elements were found across multiple ocp homolog promoters that potentially control differential transcriptional regulation in response to a range of environmental cues. The impact of distinct environmental cues on differential accumulation of ocp homolog transcripts indicates potential functional diversification of this gene family in cyanobacteria. These genes likely enable dynamic cellular protection in response to diverse environmental stress conditions in F. diplosiphon.
Highlights
Oxygenic photosynthesis, a process comprised of a series of lightdriven redox reactions that results in the production of ATP and NADPH and carbohydrates, is a characteristic feature of the metabolism of cyanobacteria
To investigate whether ocp homologs are controlled at the transcriptional level in response to changes in light availability, cultures of WT F. diplosiphon were grown under various intensities of green light (GL) and red light (RL) and RNA was harvested so that the mRNA levels of ocp homologs could be measured using quantitative real-time PCR (qPCR)
Relative expression of ocp1 and frp trended higher in low RL relative to low GL, and levels somewhat decreased with increased light intensity, these differences were not significant (Figure 1A)
Summary
A process comprised of a series of lightdriven redox reactions that results in the production of ATP and NADPH and carbohydrates, is a characteristic feature of the metabolism of cyanobacteria. Under some conditions, such as excessive light exposure or during nutrient deprivation, cyanobacteria can become unable to effectively utilize the light energy absorbed for photosynthesis. Fremyella diplosiphon exhibits a particular form of chromatic acclimation known as complementary chromatic acclimation (CCA) that involves tuning cellular pigmentation and morphology to changes in available green versus red light (Bennett and Bogorad, 1973; Bordowitz and Montgomery, 2008). Complementary chromatic acclimation is regulated by the red/green-responsive photoreceptor RcaE (Kehoe and Grossman, 1996; Bordowitz and Montgomery, 2008)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.