Post-transcriptional reprogramming during root nodule symbiosis

Abstract

Plant cells adjust their genetic programs integrating developmentaland environmental cues, leading to a constantreprogramming in gene expression that contributes to thephysiological and ecological adaptation of the whole plant.Legume plants establish a nitrogen fixing symbiosis with soilbacteria known as rhizobia, providing an exquisite biologicalmodel to study reprogramming of gene expression in a pluricellulareukaryotic organism interacting with its prokaryoticmicrosymbiont in a changing environmental context, whichalso impacts on the output of the symbiotic association. Manystudies in this field have focused on the modification of theplant transcriptome during the onset of the interaction, takingadvantage of the DNA microarray and direct RNA sequencing(RNA-seq) technologies. As a consequence, most of theinformation available describes changes in the steady-statelevels of poly A+ RNAs at different stages of the interaction (ElYahyaoui et al. 2004; Lohar et al. 2006; Benedito et al. 2008;Breakspear et al. 2014; Roux et al. 2014), underestimating thepost-transcriptional mechanisms that add new layers of regulationto the reprogramming of gene expression. In the last years,a number of studies have contributed to a more comprehensiveunderstanding of these changes, highlighting the importance ofthe stability and translatability of poly A+ RNAs, as well as therole of endogenous small RNAs (sRNAs), mainly microRNAs(miRNAs) and phased small interfering RNAs (phasiRNAs),as key regulators of gene expression. In this chapter, we willsummarize the contribution of translational regulation to thegenetic responses of the plant during root nodule symbiosisand the crucial roles played by sRNAs in this ecologically andagronomically important interaction.