The micro-RNA72c-APETALA2-1 node as a key regulator of the common bean-Rhizobium etli nitrogen fixation symbiosis

Plant Physiol. 2015 May;168(1):273-91. doi: 10.1104/pp.114.255547. Epub 2015 Mar 4.


Micro-RNAs are recognized as important posttranscriptional regulators in plants. The relevance of micro-RNAs as regulators of the legume-rhizobia nitrogen-fixing symbiosis is emerging. The objective of this work was to functionally characterize the role of micro-RNA172 (miR172) and its conserved target APETALA2 (AP2) transcription factor in the common bean (Phaseolus vulgaris)-Rhizobium etli symbiosis. Our expression analysis revealed that mature miR172c increased upon rhizobial infection and continued increasing during nodule development, reaching its maximum in mature nodules and decaying in senescent nodules. The expression of AP2-1 target showed a negative correlation with miR172c expression. A drastic decrease in miR172c and high AP2-1 mRNA levels were observed in ineffective nodules. Phenotypic analysis of composite bean plants with transgenic roots overexpressing miR172c or a mutated AP2-1 insensitive to miR172c cleavage demonstrated the pivotal regulatory role of the miR172 node in the common bean-rhizobia symbiosis. Increased miR172 resulted in improved root growth, increased rhizobial infection, increased expression of early nodulation and autoregulation of nodulation genes, and improved nodulation and nitrogen fixation. In addition, these plants showed decreased sensitivity to nitrate inhibition of nodulation. Through transcriptome analysis, we identified 114 common bean genes that coexpressed with AP2-1 and proposed these as being targets for transcriptional activation by AP2-1. Several of these genes are related to nodule senescence, and we propose that they have to be silenced, through miR172c-induced AP2-1 cleavage, in active mature nodules. Our work sets the basis for exploring the miR172-mediated improvement of symbiotic nitrogen fixation in common bean, the most important grain legume for human consumption.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Gene Expression Profiling
  • Gene Expression Regulation, Plant / drug effects
  • Gene Ontology
  • Genes, Plant
  • MicroRNAs / genetics
  • MicroRNAs / metabolism
  • Models, Biological
  • Nitrates / pharmacology
  • Nitrogen Fixation* / drug effects
  • Nitrogen Fixation* / genetics
  • Phaseolus / drug effects
  • Phaseolus / genetics
  • Phaseolus / microbiology*
  • Phaseolus / physiology*
  • Plant Proteins / genetics
  • Plant Proteins / metabolism*
  • Plant Root Nodulation / drug effects
  • Plant Root Nodulation / genetics
  • Plant Roots / drug effects
  • Plant Roots / genetics
  • Plant Roots / microbiology
  • Protein Isoforms
  • RNA, Messenger / genetics
  • RNA, Messenger / metabolism
  • Rhizobium etli / drug effects
  • Rhizobium etli / physiology*
  • Symbiosis* / drug effects
  • Symbiosis* / genetics


  • MicroRNAs
  • Nitrates
  • Plant Proteins
  • Protein Isoforms
  • RNA, Messenger