A mi R 169 isoform regulates specific NF ‐ YA targets and root architecture in A rabidopsis

Summary In plants, roots are essential for water and nutrient acquisition. Micro RNA s (mi RNA s) regulate their target m RNA s by transcript cleavage and/or inhibition of protein translation and are known as major post‐transcriptional regulators of various developmental pathways and stress responses. In A rabidopsis thaliana , four isoforms of mi R 169 are encoded by 14 different genes and target diverse m RNA s, encoding subunits A of the NF ‐ Y transcription factor complex. These mi RNA isoforms and their targets have previously been linked to nutrient signalling in plants. By using mimicry constructs against different isoforms of mi R 169 and mi R ‐resistant versions of NF ‐ YA genes we analysed the role of specific mi R 169 isoforms in root growth and branching. We identified a regulatory node involving the particular mi R 169defg isoform and NF ‐ YA 2 and NF ‐ YA 10 genes that acts in the control of primary root growth. The specific expression of MIM 169defg constructs altered specific cell type numbers and dimensions in the root meristem. Preventing mi R 169defg‐regulation of NF ‐ YA 2 indirectly affected laterial root initiation. We also showed that the mi R 169defg isoform affects NF ‐ YA 2 transcripts both at m RNA stability and translation levels. We propose that a specific mi R 169 isoform and the NF ‐ YA 2 target control root architecture in A rabidopsis.