Dynamics of cytoplamic RNAs at early stages of the nitrogen fixing symbiosis between legumes and rhizobia

MARÍA EUGENIA ZANETTI

Piriápolis

Congreso; XV JORNADAS DE LA SOCIEDAD URUGUAYA DE BIOCIENCIAS; 2014

Sociedad Uruguaya de Biociencias

Regulation of gene expression occurs at multiple levels within eukaryotic cells, including chromatin-based, transcriptional and post-transcriptional events. In the cytoplasm, mRNAs can be recruited by the translational machinery to form polysomes (mRNAs with ≥ 2 ribosomes), sequestered into translational inactive storage granules or targeted to degradation into processing bodies. Translating Ribosome Affinity Purification (TRAP) is a technology developed to specifically isolate the population of mRNAs associated with at least one ribosome, referred as the translatome. By the use of TRAP we have previously identified mRNAs and small RNAs that are selectively recruited to polysomes at early stages of the root nodule symbiosis between Medicago truncatula and Sinorhizobium meliloti. More recently, we combined TRAP with high throughput sequencing of RNA (RNA-seq) to characterize changes in the translatome in response to rhizobial infection. This analysis identified a number of mRNAs that significantly increased or decreased their levels of association with ribosomes. The first category includes genes that play essential roles in nodulation (e.g., a pectate lyase and a SINA family member). The second category contains transcripts that dissociate from polysomes upon rhizobial infection and is represented by NCR secreted peptides, receptor-like kinases and SAUR-auxin responsive proteins. Quantitative analysis of the small RNA population revealed that both microRNAs and tasiRNAs associates to polysomes and some of them change their abundance or degree of association to polysomes in response to rhizobia. The importance of dynamic partitioning of cytoplasmic mRNAs, as well as microRNA-mediated post-transcriptional regulation during root nodule symbiosis will be discussed.