Laser Capture Micro-Dissection Coupled to RNA Sequencing: A Powerful Approach Applied to the Model Legume Medicago truncatula in Interaction with Sinorhizobium meliloti.

Understanding the development of multicellular organisms requires the identification of regulators, notably transcription factors, and specific transcript populations associated with tissue differentiation. Laser capture microdissection (LCM) is one of the techniques that enable the analysis of distinct tissues or cells within an organ. Coupling this technique with RNA sequencing (RNAseq) makes it extremely powerful to obtain a genome-wide and dynamic view of gene expression. Moreover, RNA sequencing allows two or potentially more interacting organisms to be analyzed simultaneously. In this chapter, a LCM-RNAseq protocol optimized for root and symbiotic root nodule analysis is presented, using the model legume Medicago truncatula (in interaction with Sinorhizobium meliloti in the nodule samples). This includes the description of procedures for plant material fixation, embedding, and micro-dissection; it is followed by a presentation of techniques for RNA extraction and amplification, adapted for the simultaneous analysis of plant and bacterial cells in interaction or, more generally, polyadenylated and non-polyadenylated RNAs. Finally, step-by-step statistical analyses of RNAseq data are described. Those are critical for quality assessment of the whole procedure and for the identification of differentially expressed genes.