The most represented group of resistance genes are those of the nucleotide binding site–leucine-rich repeat (NBS-LRR) class. These genes are very numerous in the plant genome, and they often occur in clusters at speciﬁc loci following gene duplication and ampliﬁcation events. To date, hundreds of resistance genes and relatively few quantitative trait loci for plant resistance to pathogens have been mapped in different species, with some also cloned. When these NBS-LRR genes have been physically or genetically mapped, many cases have shown co-localization between resistance loci and NBS-LRR genes. This has allowed the identification of candidate genes for resistance, and the development of molecular markers linked to R genes. This review is focused on recent genomics studies that have described the abundance, distribution and evolution of NBS-LRR genes in plant genomes. Furthermore, in terms of their expression, NBS-LRR genes are under fine regulation by cis- and trans-acting elements. Recent findings have provided insights into the roles of alternative splicing, the ubiquitin/ proteasome system, and miRNAs and secondary siRNAs in the regulation of NBS-LRR gene expression at the post-transcriptional, post-translational and epigenetic levels. The possibility to use this knowledge for genetic improvement of plant resistance to pathogens is discussed.

/pdf/plant-nucleotide-binding-site-leucine-rich-repeat-nbs-lrr-209eqj5kfc.pdf

Plant Nucleotide Binding Site–Leucine-Rich Repeat (NBS-LRR) Genes: Active Guardians in Host Defense Responses

Yield stability of legume crops is constrained by a number of pest and diseases Major diseases are rusts, powdery and downy mildews, ascochyta blights, botrytis gray molds, anthracnoses, damping-off, root rots, collar rots, vascular wilts and white molds Parasitic weeds, viruses, bacteria, nematodes and damages caused by chewing and sap-sucking insects add to this long list of constraints for legume production Their incidence and relative importance together with current understanding of their interactions with the host plants are presented State of the art of current achievements and limitations for breeding for biotic stress resistance are listed and critically discussed The recent development of large scale phenotyping, genome sequencing and analysis of gene, protein and metabolite expressions can be of great help to further decipher plant-pathogen interactions and identify key resistance components that may be introgressed into crop plants through breeding

https://digital.csic.es/bitstream/10261/160300/1/legume_breeding_Rubiales.pdf

Achievements and Challenges in Legume Breeding for Pest and Disease Resistance

Plant disease resistance (R) genes that mediate recognition of the same pathogen determinant sometimes can be found in distantly related plant families. This observation implies that some R gene alleles may have been conserved throughout the diversification of land plants. To address this question, we have compared R genes from Glycine max (soybean), Rpg1-b, and Arabidopsis thaliana, RPM1, that mediate recognition of the same type III effector protein from Pseudomonas syringae, AvrB. RPM1 has been cloned previously, and here, we describe the isolation of Rpg1-b. Although RPM1 and Rpg1-b both belong to the coiled-coil nucleotide binding site (NBS) Leu-rich repeat (LRR) class of R genes, they share only limited sequence similarity outside the conserved domains characteristic of this class. Phylogenetic analyses of A. thaliana and legume NBS-LRR sequences demonstrate that Rpg1-b and RPM1 are not orthologous. We conclude that convergent evolution, rather than the conservation of an ancient specificity, is responsible for the generation of these AvrB-specific genes.

Convergent Evolution of Disease Resistance Gene Specificity in Two Flowering Plant Families

Stearoyl-acyl carrier protein-desaturase (SACPD)-catalyzed synthesis of oleic acid (18:1) is an essential step in fatty acid biosynthesis. Arabidopsis mutants (ssi2) with reduced SACPD activity accumulate salicylic acid (SA) and exhibit enhanced resistance to multiple pathogens. We show that reduced levels of 18:1 induce similar defense-related phenotypes in soybean. A Bean pod mottle virus (BPMV)-based vector was employed to effectively silence soybean SACPDs. The silenced plants contained reduced 18:1 and increased stearic acid, developed spontaneous cell death lesions, increased SA accumulation, and constitutively expressed pathogenesis-related genes. These plants also expressed elevated levels of resistance-like genes and showed resistance to bacterial and oomycete pathogens. Exogenous application of glycerol induced similar phenotypes, mimicking the effect of silencing SACPDs in healthy soybean plants. Overexpression of a soybean SACPD increased 18:1 levels in ssi2 but not in wild-type Arabidopsis plants, suggesting that the soybean enzyme was under feedback regulation similar to that of the Arabidopsis isozymes. These results suggest that soybean and Arabidopsis respond similarly to 18:1-derived cues by inducing a novel broad-spectrum resistance-conferring pathway, even though they differ significantly in their lipid biosynthetic pathways. We also demonstrate the efficacy of BPMV-induced gene silencing as a tool for functional studies in soybean.

https://apsjournals.apsnet.org/doi/pdf/10.1094/MPMI-21-5-0564

An oleic acid-mediated pathway induces constitutive defense signaling and enhanced resistance to multiple pathogens in soybean.

Whole-genome sequencing is fundamental to understanding the genetic composition of an organism. Given the size and complexity of the soybean genome, an alternative approach is targeted random-gene ...

A compilation of soybean ESTs: generation and analysis.

Alleles or tightly linked genes at the soybean (Glycine max L. Merr.) Rpg1 locus confer resistance to strains of Pseudomonas syringae pv. glycinea that express the avirulence genes avrB or avrRpm1. We have previously mapped Rpg1-b (the gene specific for avrB) to a cluster of resistance genes (R genes) with diverse specificities in molecular linkage group F. Here, we describe the high-resolution physical and genetic mapping of Rpg1-b to a 0.16-cM interval encompassed by two overlapping BAC clones spanning approximately 270 kilobases. Rpg1-b is part of a complex locus containing numerous genes related to previously characterized coiled coil-nucleotide binding site-leucine rich repeat (CC-NBS-LRR)-type R genes that are spread throughout this region. Phylogenetic and Southern blot analyses group these genes into four distinct subgroups, some of which are conserved in the common bean, Phaseolus vulgaris, indicating that this R gene cluster may predate the divergence of Phaseolus and Glycine. Members from different subgroups are physically intermixed and display a high level of polymorphism between soybean cultivars, suggesting that this region is rearranging at a high frequency. At least five CC-NBS-LRR-type genes cosegregate with Rpg1-b in our large mapping populations.

Genetic and physical localization of the soybean Rpg1-b disease resistance gene reveals a complex locus containing several tightly linked families of NBS-LRR genes.

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Genetic and physical localization of the soybean Rpg1-b disease resistance gene reveals a complex locus containing several tightly linked families of NBS-LRR genes.