Dataset Information

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.

SUBMITTER: Rose LE

PROVIDER: S-EPMC1840093 | biostudies-literature | 2007 Mar

REPOSITORIES: biostudies-literature

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Natural variation in the Pto disease resistance gene within species of wild tomato (Lycopersicon). II. Population genetics of Pto.

Rose Laura E LE Michelmore Richard W RW Langley Charles H CH

Genetics 20061218 3

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 coev ...[more]

PMID: 17179076

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Project description:BackgroundPlant-produced specialised metabolites are a powerful part of a plant's first line of defence against herbivorous insects, bacteria and fungi. Wild ancestors of present-day cultivated tomato produce a plethora of acylsugars in their type-I/IV trichomes and volatiles in their type-VI trichomes that have a potential role in plant resistance against insects. However, metabolic profiles are often complex mixtures making identification of the functionally interesting metabolites challenging. Here, we aimed to identify specialised metabolites from a wide range of wild tomato genotypes that could explain resistance to vector insects whitefly (Bemisia tabaci) and Western flower thrips (Frankliniella occidentalis). We evaluated plant resistance, determined trichome density and obtained metabolite profiles of the glandular trichomes by LC-MS (acylsugars) and GC-MS (volatiles). Using a customised Random Forest learning algorithm, we determined the contribution of specific specialised metabolites to the resistance phenotypes observed.ResultsThe selected wild tomato accessions showed different levels of resistance to both whiteflies and thrips. Accessions resistant to one insect can be susceptible to another. Glandular trichome density is not necessarily a good predictor for plant resistance although the density of type-I/IV trichomes, related to the production of acylsugars, appears to correlate with whitefly resistance. For type VI-trichomes, however, it seems resistance is determined by the specific content of the glands. There is a strong qualitative and quantitative variation in the metabolite profiles between different accessions, even when they are from the same species. Out of 76 acylsugars found, the random forest algorithm linked two acylsugars (S3:15 and S3:21) to whitefly resistance, but none to thrips resistance. Out of 86 volatiles detected, the sesquiterpene α-humulene was linked to whitefly susceptible accessions instead. The algorithm did not link any specific metabolite to resistance against thrips, but monoterpenes α-phellandrene, α-terpinene and β-phellandrene/D-limonene were significantly associated with susceptible tomato accessions.ConclusionsWhiteflies and thrips are distinctly targeted by certain specialised metabolites found in wild tomatoes. The machine learning approach presented helped to identify features with efficacy toward the insect species studied. These acylsugar metabolites can be targets for breeding efforts towards the selection of insect-resistant cultivars.

Dataset Information

Natural variation in the Pto disease resistance gene within species of wild tomato (Lycopersicon). II. Population genetics of Pto.

Publications

Natural variation in the Pto disease resistance gene within species of wild tomato (Lycopersicon). II. Population genetics of Pto.

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