Dynamic regulation of cytoplasmic mRNAs and small RNAs during root nodule symbiosis.

MARIA EUGENIA ZANETTI

Iguazu

Congreso; 11th International Plant Molecular Biology Congress (IPMB2015); 2015

IPMB

Regulation of gene expression occurs at multiple levels within eukaryotic cells, including chromatin-based, transcriptional and post-transcriptional events. In the cytoplasm, protein coding mRNAs are regulated at the translational level, but also by the action of small RNAs (sRNAs) that affect either stability or translatability of target mRNAs. Translating Ribosome Affinity Purification (TRAP) combined with RNA-seq allows the characterization of mRNA and sRNA populations associated to polysomes (referred as the translatome). The characterization of dynamic changes in the translatome of Medicago truncatula roots at early stages of the root nodule symbiosis (RNS) led us to the identification of mRNAs that significantly increased or decreased their levels of association with polysomes, some of which play essential roles in nodulation (e.g., pectate lyase, SINA, NCR secreted peptides). Quantitative analysis of the sRNA population revealed that both microRNAs and tasiRNAs associate to polysomes. Among them, miR169 and miR172 exhibited high percentages of association to polysome in non-inoculated roots (20% and 42%, respectively), but its association decreased during RNS. On the other hand, miR390 and TAS3-derived tasiRNAs were barely associated to polysomes, but significantly decrease their total RNA abundance at early stages of RNS. Activation of the miR390/TAS3 pathway by overexpression of miR390 in M. truncatula roots impaired nodule organogenesis, rhizobial infection and the expression of nodulation signaling genes, whereas inactivation of this pathway increased the number of nodules and altered their spatial distribution. These results indicate that the miR390/TAS3 pathway might act in the control of both nodule organogenesis and rhizobial infection morphogenetic programs.