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Evidence of cryptic introgression in tomato (Solanum lycopersicum L.) based on wild tomato species alleles.

ABSTRACT: BACKGROUND: Many highly beneficial traits (e.g. disease or abiotic stress resistance) have been transferred into crops through crosses with their wild relatives. The 13 recognized species of tomato (Solanum section Lycopersicon) are closely related to each other and wild species genes have been extensively used for improvement of the crop, Solanum lycopersicum L. In addition, the lack of geographical barriers has permitted natural hybridization between S. lycopersicum and its closest wild relative Solanum pimpinellifolium in Ecuador, Peru and northern Chile. In order to better understand patterns of S. lycopersicum diversity, we sequenced 47 markers ranging in length from 130 to 1200?bp (total of 24?kb) in genotypes of S. lycopersicum and wild tomato species S. pimpinellifolium, Solanum arcanum, Solanum peruvianum, Solanum pennellii and Solanum habrochaites. Between six and twelve genotypes were comparatively analyzed per marker. Several of the markers had previously been hypothesized as carrying wild species alleles within S. lycopersicum, i.e., cryptic introgressions. RESULTS: Each marker was mapped with high confidence (e<1 x 10-30) to a single genomic location using BLASTN against tomato whole genome shotgun chromosomes (SL2.40) database. Neighbor-joining trees showed high mean bootstrap support (86.8 ± 2.34%) for distinguishing red-fruited from green-fruited taxa for 38 of the markers. Hybridization and parsimony splits networks, genomic map positions of markers relative to documented introgressions, and historical origins of accessions were used to interpret evolutionary patterns at nine markers with putatively introgressed alleles. CONCLUSION: Of the 47 genetic markers surveyed in this study, four were involved in linkage drag on chromosome 9 during introgression breeding, while alleles at five markers apparently originated from natural hybridization with S. pimpinellifolium and were associated with primitive genotypes of S. lycopersicum. The positive identification of introgressed genes within crop species such as S. lycopersicum will help inform conservation and utilization of crop germplasm diversity, for example, facilitating the purging of undesirable linkage drag or the exploitation of novel, favorable alleles.

SUBMITTER: Labate JA

PROVIDER: S-EPMC3462117 | biostudies-literature | 2012

REPOSITORIES: biostudies-literature

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Evidence of cryptic introgression in tomato (Solanum lycopersicum L.) based on wild tomato species alleles.

Labate Joanne A JA Robertson Larry D LD

BMC plant biology 20120807

<h4>Background</h4>Many highly beneficial traits (e.g. disease or abiotic stress resistance) have been transferred into crops through crosses with their wild relatives. The 13 recognized species of tomato (Solanum section Lycopersicon) are closely related to each other and wild species genes have been extensively used for improvement of the crop, Solanum lycopersicum L. In addition, the lack of geographical barriers has permitted natural hybridization between S. lycopersicum and its closest wild ...[more]

PMID: 22871151

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Project description:BackgroundEndogenous pararetroviral sequences (EPRVs) are a recently discovered class of repetitive sequences that is broadly distributed in the plant kingdom. The potential contribution of EPRVs to plant pathogenicity or, conversely, to virus resistance is just beginning to be explored. Some members of the family Solanaceae are particularly rich in EPRVs. In previous work, EPRVs have been characterized molecularly in various species of Nicotiana including N.tabacum (tobacco) and Solanum tuberosum (potato). Here we describe a family of EPRVs in cultivated tomato (Solanum lycopersicum L.) and a wild relative (S.habrochaites).ResultsMolecular cloning and DNA sequence analysis revealed that tomato EPRVs (named LycEPRVs) are most closely related to those in tobacco. The sequence similarity of LycEPRVs in S.lycopersicum and S.habrochaites indicates they are potentially derived from the same pararetrovirus. DNA blot analysis revealed a similar genomic organization in the two species, but also some independent excision or insertion events after species separation, or flanking sequence divergence. LycEPRVs share with the tobacco elements a disrupted genomic structure and frequent association with retrotransposons. Fluorescence in situ hybridization revealed that copies of LycEPRV are dispersed on all chromosomes in predominantly heterochromatic regions. Methylation of LycEPRVs was detected in CHG and asymmetric CHH nucleotide groups. Although normally quiescent EPRVs can be reactivated and produce symptoms of infection in some Nicotiana interspecific hybrids, a similar pathogenicity of LycEPRVs could not be demonstrated in Solanum L. section Lycopersicon [Mill.] hybrids. Even in healthy plants, however, transcripts derived from multiple LycEPRV loci and short RNAs complementary to LycEPRVs were detected and were elevated upon infection with heterologous viruses encoding suppressors of PTGS.ConclusionThe analysis of LycEPRVs provides further evidence for the extensive invasion of pararetroviral sequences into the genomes of solanaceous plants. The detection of asymmetric CHH methylation and short RNAs, which are hallmarks of RNAi in plants, suggests that LycEPRVs are controlled by an RNA-mediated silencing mechanism.

Project description:We have studied a genomic library of introgression lines from the Solanum pimpinellifolium accession TO-937 into the genetic background of the "Moneymaker" cultivar in order to evaluate the accession's breeding potential. Overall, no deleterious phenotypes were observed, and the plants and fruits were phenotypically very similar to those of "Moneymaker," which confirms the feasibility of translating the current results into elite breeding programs. We identified chromosomal regions associated with traits that were both vegetative (plant vigor, trichome density) and fruit-related (morphology, organoleptic quality, color). A trichome-density locus was mapped on chromosome 10 that had not previously been associated with insect resistance, which indicates that the increment of trichomes by itself does not confer resistance. A large number of quantitative trait loci (QTLs) have been identified for fruit weight. Interestingly, fruit weight QTLs on chromosomes 1 and 10 showed a magnitude effect similar to that of QTLs previously defined as important in domestication and diversification. Low variability was observed for fruit-shape-related traits. We were, however, able to identify a QTL for shoulder height, although the effects were quite low, thus demonstrating the suitability of the current population for QTL detection. Regarding organoleptic traits, consistent QTLs were detected for soluble solid content (SSC). Interestingly, QTLs on chromosomes 2 and 9 increased SSC but did not affect fruit weight, making them quite promising for introduction in modern cultivars. Three ILs with introgressions on chromosomes 1, 2, and 10 increased the internal fruit color, making them candidates for increasing the color of modern cultivars. Comparing the QTL detection between this IL population and a recombinant inbred line population from the same cross, we found that QTL stability across generations depended on the trait, as it was very high for fruit weight but low for organoleptic traits. This difference in QTL stability may be due to a predominant additive gene action for QTLs involved in fruit weight, whereas epistatic and genetic background interactions are most likely important for the other traits.

Dataset Information

Evidence of cryptic introgression in tomato (Solanum lycopersicum L.) based on wild tomato species alleles.

Publications

Evidence of cryptic introgression in tomato (Solanum lycopersicum L.) based on wild tomato species alleles.

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