Selective recruitment of mRNAs and miRNAs to polyribosomes in response to rhizobia infection in Medicago truncatula

REYNOSO, MAURICIO; BLANCO, FLAVIO; BAILEY-SERRES; CRESPI, MARTÍN; ZANETTI, MARÍA EUGENIA

Hyderabad

Congreso; VI international Congress on Legume Genetics and Genomics (ICLGG); 2012

Selective recruitment of mRNAs and miRNAs to polyribosomes in response to rhizobia infection in Medicago truncatula   Reynoso MA1*, Blanco FA1, Bailey-Serres J2, Crespi M3 and Zanetti ME1   1Instituto de Biotecnología y Biología Molecular, FCE-UNLP CCT-CONICET, Argentina.  2Department of Botany and Plant Sciences, Center for Plant Cell Biology, University of California, Riverside, USA. 3Institut des Sciences du Végétal, CNRS, Gif sur Yvette, France. *E-mail : mauricio_a_reynoso@yahoo.com.ar   Abstract Translation of mRNAs is a key regulatory step that contributes to the coordination and modulation of eukaryotic gene expression during development or adaptation to the environment. mRNA stability or translatability can be regulated by the action of small regulatory RNAs (sRNAs), which control diverse biological processes.  Under low nitrogen conditions, leguminous plants associate with soil bacteria and develop a new organ specialized in nitrogen fixation, the nodule. To gain insight into the translational regulation of mRNAs during nodule formation, the association of mRNAs and sRNAs to polysomes was characterized in roots of the model legume Medicago truncatula during the symbiotic interaction with Sinorhizobium meliloti.  Quantitative comparison of steady-state and polysomal mRNAs for fifteen genes involved in nodulation identified a group of transcripts with slight or no change in total cellular abundance that were significantly up-regulated at the level of association with polysomes in response to rhizobia. This group included mRNAs encoding three receptors like kinases required either for nodule organogenesis, bacterial infection or both and transcripts encoding GRAS and NF-Y transcription factors.  Quantitative analysis of sRNAs in total and polsyomal RNA samples revealed that mature microRNAs (miRNAs) were associated with the translational machinery, notably, miR169d/l, which targets the NF-YA/HAP2 mRNA. Upon inoculation, levels of miR169d/l pronouncedly decreased in polysomal complexes, concomitant with increased accumulation of NF-YA/HAP2 protein. These results indicate that both mRNAs and miRNAs are subjected to a differential recruitment to polysomes and expose the importance of selective mRNA translation during root nodule symbiosis.