Influence of phytochromes on microRNA expression, phenotype, and photosynthetic activity in A. thaliana phy mutants under light with different spectral composition.

Light-induced changes in miRNAs, morphogenesis, and photosynthetic processes in phytochrome-deficient mutant plants grown under different light qualities were studied. miRNA activity in many processes is regulated by phytochromes and phytochrome-interacting factors (PIFs). The reduced content of photoreceptors in phytochrome mutants affects the PIF-microRNA interaction. In plants grown under red light (RL) and white light (WL), the phenotype of phyb mutant was distorted; however, under blue light (BL) conditions, the phyb phenotype was normalized. The photosynthetic rates of both the mutants and wild type were higher under BL than under RL and WL. The expression of most studied miRNAs increased in phyaphyb mutants under BL conditions, which is probably one of the reasons for the normalization of the phenotype, the increase in PSII activity, and the photosynthetic rate. MicroRNAs under BL can partially improve photosynthesis and phenotype of the mutants, which indicates the conjugation of the functioning of phytochromes in miRNA formation.