Abstract
In photosynthetic organisms, photoprotection to avoid overexcitation of photosystems is a prerequisite for survival. Green algae have evolved light-inducible photoprotective mechanisms mediated by genes such as light-harvesting complex stress-related (LHCSR). Studies on the light-dependent regulation of LHCSR expression in the green alga Chlamydomonas reinhardtii have revealed that photoreceptors for blue light (phototropin) and ultraviolet light perception (UVR8) play key roles in initiating photoprotective signal transduction. Although initial light perception via phototropin or UVR8 is known to result in increased LHCSR3 and LHCSR1 gene expression, respectively, the mechanisms of signal transduction from the input (light perception) to the output (gene expression) remain unclear. In this study, to further elucidate the signal transduction pathway of the photoprotective response of green algae, we established a systematic screening protocol for UV-inducible LHCSR1 gene expression mutants using a bioluminescence reporter assay. Following random mutagenesis screening, we succeeded in isolating mutants deficient in LHCSR1 gene and protein expression after UV illumination. Further characterization revealed that the obtained mutants could be separated into 3 different phenotype groups, the “UV-specific”, “LHCSR1-promoter/transcript-specific” and “general photoprotective” mutant groups, which provided further insight into photoprotective signal transduction in C. reinhardtii.
Highlights
In photosynthesis, solar energy is utilized by photochemical reactions in two photosystems (PSI and PSII)[1]
Allorent et al reported that LHCSR1 and PSBS gene expression is mainly under the control of ultraviolet (UV) signal transduction, which is initiated by UV perception via the photoreceptor UVR811
The deficiency in UVR8 resulted in severe chlorophyll bleaching under HL11, suggesting that the presence of LHCSR1 and/or PSBS effectively protect PSII under light with UV components because UV light is very detrimental to the oxygen-evolving manganese cluster of PSII15
Summary
Solar energy is utilized by photochemical reactions in two photosystems (PSI and PSII)[1]. LHCSR1, thermally dissipates excitation energy on the light-harvesting complex II (LHCII), and mediates it from LHCII to PSI at low pH, allowing green algae to alleviate overexcitation of PSII at the cost of PSI excitation[13] These NPQ-related proteins play crucial roles in photoprotection in both land plants and green algae. To elucidate the signal transduction pathways in C. reinhardtii, we established a systematic forward mutagenesis screening protocol based on a luciferase-dependent bioluminescence reporter assay In this system, we fused a firefly luciferase to the LHCSR1 gene (including its 5′ UTR sequences) for monitoring UV-dependent activation of LHCSR1 expression as described in a previous study[17]. Among the DSR mutants isolated, three displayed a severe chlorophyll bleaching phenotype under HL conditions, implying that the mutants were deficient in UV-inducible photoprotection and overall photoprotection
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
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 callDisclaimer: 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.
