The arms race is ancient history in Arabidopsis, the wildflower

Abstract

Plant pathology was born after the nineteenth-century potato famine, and since then insightful genetic experiments have contributed to the great progress in our understanding of disease control. Our current view of plant resistance focuses on numerous polymorphic resistance loci, which contain genes known as R genes. The complete sequence of the Arabidopsis thaliana genome provides a framework for exploring the 'big bang' of R genes that occurred and how R genes evolved in plants from their associations with microorganisms, and for improving strategies for more sustainable deployment of disease resistance in crops.

Rapid linkage disequilibrium decay in the Lr10 gene in wild emmer wheat (Triticum dicoccoides) populations

“…The ancient diversity observed in the current study supports a long evolutionary history of Lr10 -pathogen effector interaction in the "trench warfare" model where polymorphism is maintained by alleles that are recycling between high and low frequencies shifted by frequency dependent selection (Holub 2001;Stahl et al 1999). The long coalescent time is also supported by the significant Tajima Resistance tests with a leaf rust isolate which is avirulent to Lr10 of bread wheat did not detect any Understanding LD decay patterns is essential when conducting association studies or for estimating rates of recombination.…”

“…In some R-genes, diversity is maintained by frequency dependent selection where alleles are cycled between high and low frequency in a long co-evolution with pathogens in a form of "trench warfare". The trench warfare model predicts that the polymorphism will be old and under balancing selection (Holub 2001;Stahl et al 1999). Although many studies of R-gene diversity were previously described (reviewed in Mcdowell and Simon (2006)), most of them were limited to a few alleles or to paralogs and only a few studies focused on population genetics (Mauricio et al 2003;Meaux and Neema 2003;Butterbach 2007;Yahiaoui et al 2008;Kuang et al 2008).…”

Natural history of Arabidopsis thaliana and oomycete symbioses

“…Molecular milestones from A. thaliana-oomycete pathology have added appreciably to the Linnaean-like effort to name and classify gene families (Table 1; Holub 2001Holub , 2006Holub , 2007. For example, naturally variable genes that control HpA isolate specific downy mildew resistance were among the first pathogen recognition genes (so-called R-genes) to be molecularly characterised from plants.…”

“…These abundant genes in monocots and dicots encode receptor-like proteins characterised by a leucine-rich repeat (LRR) domain that is typically highly mutable, and most known Rgenes also contain a nucleotide binding (NB) site. A single accession of A. thaliana will contain more than 100 full length NB-LRR genes, many of which exhibit unusually high levels of allelic variation amongst accessions of the species collected from natural populations (Borevitz et al 2007;Clark et al 2007;Holub 2001). At least 10 such genes have been identified as genes conferring either downy mildew or white rust resistance and are distributed amongst each of the five A. thaliana chromosomes; at least half reside in major R-like gene clusters (Borhan et al 2004(Borhan et al , 2008Holub 1997Holub , 2001).…”

“…From the initial public investment in research, the knowledge gained has potential use across breeding efforts in different plant species. For instance, molecular genetics led to the discovery of numerous pathogen receptorlike genes that provide the molecular basis for downy mildew resistance in A. thaliana (Holub 2001(Holub , 2007. These major discoveries in turn have been instrumental in the early development of marker-assisted selection for disease resistance in crops (Aarts et al 1998a;Botella et al 1997;Michelmore and Wong 2008;Shen et al 2002;Speulman et al 1998).…”