Role of AtMED17 under light and dark conditions

GIUSTOZZI, MARISOL; FREYTES, SANTIAGO NICOLÁS; PABLO CERDÁN; PAULA CASATI

Congreso; LVIV Reunión Anual de SAIB; 2023

The Mediator complex is a conserved multisubunit complex that acts as a transcriptional regulator in eukaryotes at the level of assembly of the transcription preinitiation complex. Structural and biochemical studies showed that the subunits that compose it form stable subcomplexes, dividing its structure into different modules, head, middle, tail and CDK8 module (cyclin-dependent kinase). The Mediator complex plays a key role in mediating gene expression responses to changes in the environment, including light signals and UV-B radiation by coordinating the activation of specific transcription factors and the expression of genes involved in photomorphogenesis. In the head module, MED17 interacts with the middle and tail modules and participates as a structural hub of the complex. In addition, MED17 plays an integral role in gene expression responses to various environmental and developmental signals, including in responses to ultraviolet B radiation (UV-B).Light is one of the most important environmental signals for plants, the perception of the quantity, quality and duration of light induces different plant responses. Blue light is necessary for plant growth regulation includes stimulation of cotyledon expansion. However, excessive exposure to blue light can have negative effects, such as inhibition of root and hypocotyl growth, or epinasty of leaves. In addition, the combination of blue light and UV-B has different effects, among them, blue light protects plants from the effects of UV-B radiation. In addition, darkness is an abiotic stress that can have a significant impact on plant growth and development. In the absence of light, plants show different changes, such as reduced photosynthesis, reduced growth, altered gene expression, increased susceptibility to pests and diseases and accelerated senescence. Therefore, the objective of our work is to study the role of MED17 in plants in response to darkness and blue light combined with UV-B. We observed that med17 mutant plants showed less inhibition of hypocotyl growth than wild-type (WT) plants irradiated with a pulse of blue light, or with blue light supplemented with UV-B. The analysis of the hypocotyls showed that inhibition of primary root growth by blue light was lower in med17 mutant plants than in WT plants. med17 mutant plants did not show leaf epinasty after blue light exposure, when supplemented with UV-B light was also not observed epinasty in med17 mutant plants. On the other hand, after a 96 h dark treatment, in WT plants, chlorophyll and carotenoid content decreased. However, in med17 plants these compounds were not altered. A characteristic phenotype after darkness is leaf petiole elongation, WT plants showed larger petioles than med17 mutants. In addition, med17 plants presented less oxidative damage than WT plants. Together, MED17 acts both in response to different light qualities and also to darkness.