Gutierrez L, Bussell JD, Pacurar DI, Schwambach J, Pacurar M, Bellini C
Phenotypic plasticity of adventitious rooting in Arabidopsis is controlled by complex regulation of AUXIN RESPONSE FACTOR transcripts and microRNA abundance
The Plant Cell: 2009 21:3119-3132

The development of shoot-borne roots, or adventitious roots,is indispensable for mass propagation of elite genotypes. Itis a complex genetic trait with a high phenotypic plasticitydue to multiple endogenous and environmental regulatory factors.We demonstrate here that a subtle balance of activator and repressorAUXIN RESPONSE FACTOR (ARF) transcripts controls adventitiousroot initiation. Moreover, microRNA activity appears to be requiredfor fine-tuning of this process. Thus, ARF17, a target of miR160,is a negative regulator, and ARF6 and ARF8, targets of miR167,are positive regulators of adventitious rooting. The three ARFsdisplay overlapping expression domains, interact genetically,and regulate each other's expression at both transcriptionaland posttranscriptional levels by modulating miR160 and miR167availability. This complex regulatory network includes an unexpectedfeedback regulation of microRNA homeostasis by direct and nondirecttarget transcription factors. These results provide evidenceof microRNA control of phenotypic variability and are a significantstep forward in understanding the molecular mechanisms regulatingadventitious rooting.

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