title: Patterns of divergence of a large family of nodule cysteine-rich peptides in accessions of Medicago truncatula.
abstract: The nodule cysteine-rich (NCR) groups of defensin-like (DEFL) genes are one of the largest gene families expressed in the nodules of some legume plants. They have only been observed in the inverted repeat loss clade (IRLC) of legumes, which includes the model legume Medicago truncatula. NCRs are reported to play an important role in plant-microbe interactions. To understand their diversity we analyzed their expression and sequence polymorphisms among four accessions of M. truncatula. A significant expression and nucleotide variation was observed among the genes. We then used 26 accessions to estimate the selection pressures shaping evolution among the accessions by calculating the nucleotide diversity at non-synonymous and synonymous sites in the coding region. The mature peptides of the orthologous NCRs had signatures of both purifying and diversifying selection pressures, unlike the seed DEFLs, which predominantly exhibited purifying selection. The expression, sequence variation and apparent diversifying selection in NCRs within the Medicago species indicates rapid and recent evolution, and suggests that this family of genes is actively evolving to adapt to different environments and is acquiring new functions.
authors.affiliation: Department of Plant Biology, University of Minnesota, 250 Biological Sciences, 1445 Gortner Avenue, Saint Paul, MN, 55108, USA.
authors.forename: Sumitha
authors.initials: S
authors.lastname: Nallu
authors.forename: Kevin A T
authors.initials: KA
authors.lastname: Silverstein
authors.forename: Peng
authors.initials: P
authors.lastname: Zhou
authors.forename: Nevin D
authors.initials: ND
authors.lastname: Young
authors.forename: Kathryn A
authors.initials: KA
authors.lastname: Vandenbosch
mesh_terms: D003545:Cysteine / Q000235:genetics; D023082:Defensins / Q000235:genetics*; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant / Q000235:genetics; D014644:Genetic Variation; D054884:Host-Pathogen Interactions; D046913:Medicago truncatula / Q000145:classification / Q000235:genetics* / Q000382:microbiology; D005810:Multigene Family; D020411:Oligonucleotide Array Sequence Analysis; D010455:Peptides / Q000235:genetics; D010940:Plant Proteins / Q000235:genetics*; D020641:Polymorphism, Single Nucleotide; D012045:Regulatory Sequences, Nucleic Acid / Q000235:genetics; D053204:Root Nodules, Plant / Q000235:genetics* / Q000382:microbiology; D012639:Seeds / Q000235:genetics; D020579:Sinorhizobium / Q000502:physiology; D016962:Sinorhizobium meliloti / Q000502:physiology; D013045:Species Specificity; D059467:Transcriptome
chemical_list: D023082:Defensins; D010455:Peptides; D010940:Plant Proteins; D003545:Cysteine
keywords: Medicago truncatula accessions; NCRs; diversifying selection in NCRs; expression polymorphism in NCRs; selection pressures on NCRs