Identification of ascorbate‐ and salicylate‐responsive miRNAs and verification of the spectral control of miR395 in Arabidopsis.

We assumed that miRNAs might regulate the physiological and biochemical processes in plants through their effects on the redox system and phytohormones. To check this hypothesis, the transcriptome profile of wild‐type Arabidopsis and lines with decreased ascorbate (Asc), glutathione (GSH), or salicylate (Sal) levels were compared. GSH deficiency did not influence the miRNA expression, whereas lower levels of Asc and Sal reduced the accumulation of 9 and 44 miRNAs, respectively, but only four miRNAs were upregulated. Bioinformatics analysis revealed that their over‐represented target genes are associated with the synthesis of nitrogen‐containing and aromatic compounds, nucleic acids, and sulphate assimilation. Among them, the sulphate reduction‐related miR395 – ATP‐sulfurylase couple was selected to check the assumed modulating role of the light spectrum. A greater induction of the Asc‐ and Sal‐responsive miR395 was observed under sulphur starvation in far‐red light compared to white and blue light in wild‐type and GSH‐deficient Arabidopsis lines. Sal deficiency inhibited the induction of miR395 by sulphur starvation in blue light, whereas Asc deficiency greatly reduced it independently of the spectrum. Interestingly, sulphur starvation decreased only the level of ATP sulfurylase 4 among the miR395 target genes in far‐red light. The expression level of ATP sulfurylase 3 was higher in far‐red light than in blue light in wild‐type and Asc‐deficient lines. The results indicate the coordinated control of miRNAs by the redox and hormonal system since 11 miRNAs were affected by both Asc and Sal deficiency. This process can be modulated by light spectrum, as shown for miR395. [ABSTRACT FROM AUTHOR]