MicroRNA expression profile in common bean (Phaseolus vulgaris) under nutrient deficiency stresses and manganese toxicity

MicroRNAs (miRNAs) play a pivotal role in post-transcriptional regulation of gene expression in plants. Information on miRNAs in legumes is as yet scarce. This work investigates miRNAs in an agronomically important legume, common bean (Phaseolus vulgaris). A hybridization approach employing miRNA macroarrays -printed with oligo-nucleotides complementary to 68 known miRNAs -was used to detect miRNAs in the leaves, roots and nodules of control and nutrient-stressed (phosphorus, nitrogen, or iron deficiency; acidic pH; and manganese toxicity) common bean plants. Thirty-three miRNAs were expressed in control plants and another five were only expressed under stress conditions. The miRNA expression ratios (stress: control) were evaluated using principal component and hierarchical cluster analyses. A group of miRNAs responded to nearly all stresses in the three organs analyzed. Other miRNAs showed organ-specific responses. Most of the nodule-responsive miRNAs showed up-regulation. miRNA blot expression analysis confirmed the macroarray results. Novel miRNA target genes were proposed for common bean and the expression of selected targets was evaluated by quantitative reverse transcriptase-polymerase chain reaction. In addition to the detection of previously reported stress-responsive miRNAs, we discovered novel common bean stress-responsive miRNAs, for manganese toxicity. Our data provide a foundation for evaluating the individual roles of miRNAs in common bean.