RNA-Binding Protein 1 (RBP1) was first identified as a protein partner of the long noncoding RNA (lncRNA) ENOD40 in Medicago truncatula, involved in symbiotic nodule development. RBP1 is localized in nuclear speckles and can be relocalized to the cytoplasm by the interaction with ENOD40. The two closest homologs to RBP1 in Arabidopsis thaliana were called Nuclear Speckle RNA-binding proteins (NSRs) and characterized as alternative splicing modulators of specific mRNAs. They can recognize in vivo the lncRNA ALTERNATIVE SPLICING COMPETITOR (ASCO) among other lncRNAs, regulating lateral root formation. Here, we performed a phylogenetic analysis of NSR/RBP proteins tracking the roots of the family to the Embryophytes. Strikingly, eudicots faced a reductive trend of NSR/RBP proteins in comparison with other groups of flowering plants. In Medicago truncatula and Lotus japonicus, their expression profile during nodulation and in specific regions of the symbiotic nodule was compared to that of the lncRNA ENOD40, as well as to changes in alternative splicing. This hinted at distinct and specific roles of each member during nodulation, likely modulating the population of alternatively spliced transcripts. Our results establish the basis to guide future exploration of NSR/RBP function in alternative splicing regulation in different developmental contexts along the plant lineage.

In legumes, a LysM-RLK perception of rhizobial lipo-chitooligosaccharides (LCOs) known as Nod factors (NFs), triggers a signaling pathway related to the onset of symbiosis development. On the other hand, activation of LysM-RLKs upon recognition of chitin-derived short-chitooligosaccharides initiates defense responses. In this work, we identified the members of the LysM-RLK family in cultivated (Arachis hypogaea L.) and wild (A. duranensis and A. ipaensis) peanut genomes, and reconstructed the evolutionary history of the family. Phylogenetic analyses allowed the building of a framework to reinterpret the functional data reported on peanut LysM-RLKs. In addition, the potential involvement of two identified proteins in NF perception and immunity was assessed by gene expression analyses. Results indicated that peanut LysM-RLK is a highly diverse family. Digital expression analyses indicated that some A. hypogaea LysM-RLK receptors were upregulated during the early and late stages of symbiosis. In addition, expression profiles of selected LysM-RLKs proteins suggest participation in the receptor network mediating NF and/or chitosan perception. The analyses of LysM-RLK in the non-model legume peanut can contribute to gaining insight into the molecular basis of legume–microbe interactions and to the understanding of the evolutionary history of this gene family within the Fabaceae.