Function and Evolution of the miR396 Regulatory Network

PALATNIK, JAVIER F; DEBERNARDI, JUAN MANUEL; RODRIGUEZ, RAMIRO E

Viena

Congreso; 23rd International Conference on Arabidopsis Research.; 2012

The microRNA mir396 regulates seven transcription factors of the GROWTH REGULATING FACTOR (GRF) family in Arabidopsis thaliana. Overexpression of miR396 leads to down-regulation of these GRFs and a reduced number of cells in leaves and the meristem. Conversely, transgenic plants harboring GRF transgenes with mutations in the miRNA binding sitehave more cells and bigger leaves. MiR396 accumulates in the distal part of young leaves, restricting the expression of the GRFs to the proximal part of the organ, which in turn coincides with the leaf domain undergoing cell proliferation. We have shown that the shape of the proximo-distal pattern of expression of GRF2 depends on the exact nature of the interaction with the miRNA, including a conserved bulged nucleotide. A variant of miR396, present only in monocots, has an additional nucleotide, eliminating this bulge and repressing the GRFs much more efficiently than the dicot miR396. In turn, we found that the conserved miR396 network can acquire new targets, including a bHLH transcription factor present in the sister families Brassicaceae and Cleomaceae. Still, the repression of this bHLH by miR396 is important for margin and vein pattern formation of Arabidopsis leaves, suggesting that the regulation of new targets by conserved miRNAs might be biologically important. A systematic analysis of conserved miRNA networks revealed that the acquisition of new targets by plant miRNAs might be more common than previously thought.