Abstract
Both phytohormones and non-coding microRNAs (miRNAs) play important role in root development in Arabidopsis thaliana. Mature miR166/165 s, which are derived from precursor transcripts of concerned genes, regulate developmental processes, including leaf and root patterning, by targeting Class III HOMEODOMAIN LEUCINE-ZIPPER (HD-ZIP III) transcription factors (TFs). However, their regulation through hormones remained poorly understood. Here, we show that several phytohormones dynamically regulate the spatio-temporal expression pattern of miR166/165 and target HD-ZIP IIIs in developing roots. Hormone signaling pathway mutants show differential expression pattern of miR166/165, providing further genetic evidence for multilayered regulation of these genes through phytohormones. We further show that a crosstalk of at least six different phytohormones regulate the miR166/165, their target HD-ZIP IIIs, and KANADI (KANs). Our results suggest that HD-ZIP IIIs mediated root development is modulated both transcriptionally through phytohormones and KANs, and post-transcriptionally by miR166/165 that in turn are also regulated by the phytohormonal crosstalk.
Highlights
Besides role in other developmental processes, several miRNAs have been reported to regulate root development in Arabidopsis[11]
To understand whether phytohormones regulate the expression of miR166/165 and contribute to miR166/165 mediated root development, we analyzed the expression of miR166/165 upon treatment with aforesaid phytohormones at different time intervals (1, 6, 12, and 24 hrs)
These results suggest that phytohormones dynamically regulate the expression of miR166/165 during stages of root development
Summary
Besides role in other developmental processes, several miRNAs have been reported to regulate root development in Arabidopsis[11]. Spatio-temporal expression or transcriptional pattern of different miRNA species of a family as well as their targets depends on the cis-regulatory elements, including hormone response elements, in their respective promoters. MiR165 and miR166 are the two miRNAs that differ by only one nucleotide in their mature sequence and both target transcripts of same HD-ZIP III gene family members[13]. Spatio-temporally regulated expression dynamics of a miRNA gene family is likely to regulate the expression pattern or accumulation of their target transcripts at post-transcriptional level. We have analyzed the effects of various phytohormones on the expression pattern of miR166/165 s (precursors and mature), their target HD-ZIP IIIs and KAN genes during root development. We provide evidence that it is the dose of functional HD-ZIP III transcripts, regulated both at transcriptional and post-transcriptional level, which plays important role in root development. Our results uncover a complex hormonal crosstalk regulating HD-ZIP IIIs transcript level (at transcriptional/post-transcriptional level) by modulating the expression of miR166/165, KANs and hormone signaling during root development
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