UV-B radiation delays flowering time through changes in the PRC2 complex activity and miR156 levels in Arabidopsis thaliana

UV-B is a high-energy component of the solar radiation perceived by the plant and induces a number of modifications in plant growth and development, including changes in flowering time. However, the molecular mechanisms underlying these changes are largely unknown. In the present work, we demonstrate that Arabidopsis plants grown under white light supplemented with UV-B show a delay in flowering time, and this developmental reprogramming is mediated by the UVR8 photoreceptor. Using a combination of gene expression analyses and UV-B irradiation of different flowering mutants, we gained insight into the pathways involved in the observed flowering time delay in UV-B-exposed Arabidopsis plants. We provide evidence that UV-B light downregulates the expression of MSI1 and CLF, two of the components of the polycomb repressive complex 2, which in consequence drives a decrease in H3K27me3 histone methylation of MIR156 and FLC genes. Modification in the expression of several flowering time genes as a consequence of the decrease in the polycomb repressive complex 2 activity was also determined. UV-B exposure of flowering mutants supports the involvement of this complex in the observed delay in flowering time, mostly through the age pathway.