miR393: integrator of environmental cues in auxin signaling?

Auxin signalling and plant development depend on a family of partially redundant F-box receptors of the TIR1/AFB2 Auxin Receptor (TAAR) clade. We have recently shown that the post-transcriptional regulation of the Arabidopsis thaliana TAAR gene family invokes complex sRNA regulations during development. In leaves, the microRNA miR393 appears (1) to be primarily generated from one of the two genes, AtMIR393B, (2) to regulate the expression of all four members of the clade and (3) to initiate the formation of functional secondary siRNAs, named siTAARs, from TAAR transcripts themselves. Strikingly, mir393b-1 mutants, which are impaired in the biogenesis of miR393b and siTAARs, exhibit rather mild developmental defects. The known roles of miR393 in nitrate response, in defence against pathogenic bacteria and in plant development lead us to hypothesize that miR393 plays an important role to integrate complex environmental stimuli.