Post‐transcriptional reprogramming during root nodule symbiosis

Legume plants establish a symbiosis with soil bacteria known as rhizobia, which results in the formation of a new organ specialized in nitrogen fixation, the nodule. The development of functional nodules requires a reprogramming of gene expression in root cells that are committed for symbiosis, leading to the activation of two highly coordinated morphogenetic programs, the organogenesis of the nodule and the rhizobial infection. Transcriptome studies have quantified steady-state levels of poly A+ RNA in roots and nodules to estimate changes in gene expression at different stages of the symbiotic interaction. In the last decade, several studies have highlighted the importance of post-transcriptional regulatory mechanisms that affect the stability and translatability of poly A+ RNAs and their contribution to the reprogramming of gene expression during symbiosis. In this chapter, we will summarize and discuss the translational and small RNA mediated layers of regulation of gene expression in this ecologically and agronomically important interaction.