Natural Variation in the Pto Disease Resistance Gene Within Species of Wild Tomato (Lycopersicon). II. Population Genetics of Pto

Abstract

Disease resistance to the bacterial pathogen Pseudomonas syringae pv. tomato (Pst) in the host species Lycopersicon esculentum, the cultivated tomato, and the closely related L. pimpinellifolium is triggered by the physical interaction between the protein products of the host resistance (R) gene Pto and the pathogen avirulence genes AvrPto and AvrPtoB. Sequence variation at the Pto locus was surveyed in natural populations of seven species of Lycopersicon to test hypotheses of host-parasite coevolution and functional adaptation of the Pto gene. Pto shows significantly higher nonsynonymous polymorphism than 14 other non-R-gene loci in the same samples of Lycopersicon species, while showing no difference in synonymous polymorphism, suggesting that the maintenance of amino acid polymorphism at this locus is mediated by pathogen selection. Also, a larger proportion of ancestral variation is maintained at Pto as compared to these non-R-gene loci. The frequency spectrum of amino acid polymorphisms known to negatively affect Pto function is skewed toward low frequency compared to amino acid polymorphisms that do not affect function or silent polymorphisms. Therefore, the evolution of Pto appears to be influenced by a mixture of both purifying and balancing selection.

Proteolysis of a Negative Regulator of Innate Immunity Is Dependent on Resistance Genes in Tomato and Nicotiana benthamiana and Induced by Multiple Bacterial Effectors

“…This leads to the consideration of what extent Pto/Prf-mediated resistance is similar to or different from other effector-triggered resistance systems and whether Pto and Prf are primarily involved in PAMP-or effector-triggered resistance. In the Pto/Prf pathway, the kinase gene component is multicopy and exhibits intraspecific variation in sequence and function (Riely and Martin, 2001;Rose et al, 2005Rose et al, , 2007. In other specific resistances, the genes encoding the NBS-LRR proteins are the ones that have been duplicated and are the more variable component (McHale et al, 2006).…”

Plastic Transcriptomes Stabilize Immunity to Pathogen Diversity: The Jasmonic Acid and Salicylic Acid Networks within the Arabidopsis/Botrytis Pathosystem

“…These attacks can lead to strong selective forces on the plant genome in wild ecosystems and can cause significant financial and yield losses in agricultural crops (Bergelson et al, 2001; Van der Hoorn et al, 2002;Mauricio et al, 2003;Rose et al, 2007;Fisher et al, 2012;Hörger et al, 2012;Züst et al, 2012;Karasov et al, 2014). In turn, pathogens have evolved an array of virulence mechanisms based on their infection strategy that causes a prolonged selection pressure on plants to evolve complex and coherent innate immune systems.…”

Evolution and Genetic Population Structure of Prickly Lettuce (Lactuca serriola) and Its RGC2 Resistance Gene Cluster

“…Previous studies of evolutionary and population genetics of other R-genes were done mainly on single-copy Rgenes that had no sequence exchange with paralogs (Caicedo et al 1999;Mauricio et al 2003;Caicedo and Schaal 2004;Bakker et al 2006;Rose et al 2007). These single-copy R-genes have evolutionary patterns similar to those of type II R-genes.…”