The Photoreceptors Phototropin 1 and Phytochrome B Mediate Moonlight Perception and Response in <em>Arabidopsis thaliana</em>

Early and recent studies have demonstrated that exposure to moonlight influences the entire life cycle of plants from seed germination to vegetative growth and reproduction. Exposure to moonlight was found to induce genome reorganization in plants and significant changes in gene expression, protein, and metabolite profiles. However, the specific factors that facilitate moonlight perception are unknown. To uncover the photoreceptors responsible for moonlight perception, we analyzed Arabidopsis phototropin mutants (phot1, phot2, and phot1phot2) as well as the phytochrome mutants phyA and phyB for their response to full moonlight (FML). De-etiolation assays revealed that plants do perceive and respond to FML within 5 h of exposure. Thus, among the photoreceptor mutants analyzed, only phot1 and phot1phot2 were impaired in apical hook opening and cotyledon unfolding under FML. Interestingly, under high light intensity, all examined mutants have undergone proper de-etiolation. Further analysis showed that phot1 as well as phyB mutants were impaired in response to moonlight, displaying no changes in nuclear size and in protein profiles following exposure to FML and were comparable to plants exposed to dark. The FML (5 h exposure) did not induce the formation of fewer, large nuclear photobodies as occurred following 5 h exposure to growth room light. Our findings highlighted phot1 and phyB as photoreceptors necessary for plants to perceive and respond to FML. It is proposed that the initial perception of moonlight is facilitated by the blue light receptor phot1 and is subsequently interpreted into a functional state by the R/FR receptor phyB.