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Inverse regulation of light harvesting and photoprotection is mediated by a 3'-end-derived sRNA in cyanobacteria.

ABSTRACT: Phycobilisomes (PBSs), the principal cyanobacterial antenna, are among the most efficient macromolecular structures in nature, and are used for both light harvesting and directed energy transfer to the photosynthetic reaction center. However, under unfavorable conditions, excess excitation energy needs to be rapidly dissipated to avoid photodamage. The orange carotenoid protein (OCP) senses light intensity and induces thermal energy dissipation under stress conditions. Hence, its expression must be tightly controlled; however, the molecular mechanism of this regulation remains to be elucidated. Here, we describe the discovery of a posttranscriptional regulatory mechanism in Synechocystis sp. PCC 6803 in which the expression of the operon encoding the allophycocyanin subunits of the PBS is directly and in an inverse fashion linked to the expression of OCP. This regulation is mediated by ApcZ, a small regulatory RNA that is derived from the 3'-end of the tetracistronic apcABC-apcZ operon. ApcZ inhibits ocp translation under stress-free conditions. Under most stress conditions, apc operon transcription decreases and ocp translation increases. Thus, a key operon involved in the collection of light energy is functionally connected to the expression of a protein involved in energy dissipation. Our findings support the view that regulatory RNA networks in bacteria evolve through the functionalization of mRNA 3'-UTRs.

SUBMITTER: Zhan J

PROVIDER: S-EPMC8136909 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Sunscreen and sunblock are crucial skincare products to prevent photoaging and photocarcinogenesis through the addition of chemical filters to absorb or block ultraviolet (UV) radiation. However, several sunscreen and sunblock ingredients, mostly UV filters, have been associated with human and environmental safety concerns. Therefore, the exploration and discovery of promising novel sources of efficient and safer compounds with photoprotection-related activities are currently required. Marine invertebrates, particularly their associated microbiota, are promising providers of specialized metabolites with valuable biotechnological applications. Nevertheless, despite Actinobacteria members being a well-known source of bioactive metabolites, their photoprotective potential has been poorly explored so far. Hence, a set of methanolic extracts obtained from Cliona varians-derived actinomycetes was screened regarding their antioxidant and UV-absorbing capacities (i.e., photoprotection-related activities). The active extract-producing strains were identified and classified within genera Streptomyces, Micrococcus, Gordonia, and Promicromonospora. This is the first report of the isolation of these microorganisms from C. varians (an ecologically important Caribbean coral reef-boring sponge). The in vitro cytotoxicity on dermal fibroblasts of oxybenzone and the selected active extracts revealed that oxybenzone exerted a cytotoxic effect, whereas no cytotoxic effect of test extracts was observed. Accordingly, the most active (SPFi > 5, radical scavenging > 50%) and nontoxic (cell viability > 75%) extracts were obtained from Streptomyces strains. Finally, LC-MS-based characterization suggested a broad chemical space within the test strains and agreed with the reported streptomycetes' chemodiversity. The respective metabolite profiling exposed a strain-specific metabolite occurrence, leading to the recognition of potential hits. These findings suggest that marine Streptomyces produce photoprotectants ought to be further explored in skincare applications.

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Inverse regulation of light harvesting and photoprotection is mediated by a 3'-end-derived sRNA in cyanobacteria.

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