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Review
. 2013 Jan;19(1):1-9.
doi: 10.1007/s12298-012-0138-2.

Perspectives of genomic diversification and molecular recombination towards R-gene evolution in plants

Raj Kumar Joshi  1 , Sanghamitra Nayak  1
Affiliations
Review

Perspectives of genomic diversification and molecular recombination towards R-gene evolution in plants

Raj Kumar Joshi et al. Physiol Mol Biol Plants. 2013 Jan.

Abstract

Plants are under strong evolutionary pressure in developing new and noble R genes to recognize pathogen avirulence (avr) determinants and bring about stable defense for generation after generations. Duplication, sequence variation by mutation, disparity in the length and structure of leucine rich repeats etc., causes tremendous variations within and among R genes in a plant thereby developing diverse recognitional specificity suitable enough for defense against new pathogens. Recent studies on genome sequencing, diversity and population genetics in different plants have thrown new insights on the molecular evolution of these genes. Tandem and segmental duplication are important factors in R gene abundance as inferred from the distribution of major nucleotide binding site-leucine rich repeats (NBS-LRRs) type R-genes in plant genomes. Likewise, R-gene evolution is also thought to be facilitated by cluster formation thereby causing recombination and sequence exchange and resulting in haplotypic diversity. Population studies have further proven that balancing selection is responsible for the maintenance of allelic diversity in R genes. In this review, we emphasize and discuss on improved perspectives towards the molecular mechanisms and selection pressure responsible for the evolution of NBS-LRR class resistance genes in plants.

Keywords: Diversification; Duplication; Evolution; NBS-LRRs; R-genes.

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Figures

Fig. 1
Fig. 1
Evolutionary pattern of NBS-LRR class resistance genes in plants. Diversification of TIR-NBS-LRR (group I) and non-TIR-NBS-LRR (group II) took place during differentiation of angiosperms and gymnosperms. The separation of monocot and dicot was followed by extensive gene duplication and diversification resulting in NBS-LRR genes with diverse recognitional specificities
Fig. 2
Fig. 2
Fast and slow pattern of evolution exhibited by type I and type II genes in plants. Type I clade paralogs exhibit high degree of sequence exchange thereby resulting in high haplotypic diversity. Type II gene clades exhibit occasional sequence exchanges thereby resulting in high homology among orthologs. Color lines represent the changes accumulated within R genes through evolution. Dotted line represent the evolutionary time
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