The L. pennellii Introgression Lines (ILs)
A) Population structure
We have developed, using whole genome marker analysis,
a permanent mapping population designed for QTL analysis. This resource is composed of a tomato variety
(Lycopersicon esculentum CV. M82) which includes single introgressed genomic regions from the wild green-fruited
species L. pennellii.
This congenic resource is composed of 76 introgression lines (ILs) where amongst them there is
complete coverage of the wild species genome. The ILs have been produced through successive introgression
backcrossing and marker-assisted selection to generate a set of recurrent parent lines with single
introgressed segments (Eshed and Zamir 1994).
The IL map is connected to the high-resolution F2 map composed of 1500 markers (IL chromosome maps).
Seed of the ILs are distributed by The C.M. Rick Tomato Genetics Resource Center,
University of California Davis and the ILs were assigned accession numbers LA4028 - LA4103.
B) The genetic basis of QTL variation
Gene action of quantitative trait loci (QTL) can be determined
by comparing an IL homozygous for a particular wild species introgression to its nearly isogenic hybrid with M82
which is heterozygous for the same chromosome segment. Three nearly isogenic lines (M82, IL1-1 and ILH1-1),
their genome composition and the genetic components of the QTL variation are cartooned in Figure 2.
Based on the mean phenotypic values of the lines it is possible to estimate the mode of action of the QTL
(Eshed and Zamir 1995).
C) IL bin-mapping of 'trait QTL'
The bin mapping method is exemplified in Figure 3.
The exotic accession of L. pennellii is represented by a pair of homologous chromosomes of the donor parent
(green chromosomes), the recurrent parent M82 (red chromosome) and six ILs from chromosome 1 that are presented in Figure 3.
The ILs, all of which are homozygous for the red chromosomes in the rest of the genome, constitute a set of nearly isogenic lines for chromosome 1.
The six ILs covering chromosome 1 create 10 mapping bins (1A - 1J), each with a unique donor parent composition.
A 'trait QTL' is mapped by phenotyping all lines in randomised replicated trials and presenting the results as
percent difference from the recurrent parent M82 (0 value; black bars indicate a significant difference from the
common control; empty bars indicate non-significant differences). Combined analysis of the data for all lines
defines a QTL that increases the phenotypic value to bin 1C and a reducing QTL to bin 1H. The mapping scheme
presented here was adopted from actual tomato data (Fridman et al. 2002).
Selected IL publications :
Eshed Y, M Abu-Abied, Y Saranga, D Zamir (1992) Lycopersicon esculentum lines containing small overlapping introgressions from L. pennellii. Theor Appl Genet 83:1027-1034
Eshed Y and D. Zamir (1994) Introgressions from Lycopersicon pennellii can improve the soluble-solids yield of tomato hybrids. Theor Appl Genet 88:891-897.
Eshed Y and D. Zamir (1994) A genomic library of Lycopersicon pennellii in L. esculentum: A tool for fine mapping of genes. Euphytica 79:175-179.
Eshed Y and D Zamir (1995) An introgression line population of Lycopersicon pennellii in the cultivated tomato enables the identification and fine mapping of yield associated QTL. Genetics 141:1147-1162.
Eshed Y, G Gera and D Zamir (1996) A genome-wide search for wild-species alleles that increase horticultural yield of processing tomatoes Theor Appl Genet 93: 877-886.
Eshed Y and D Zamir (1996) Less than additive epistatic interactions of QTL in tomato. Genetics 143:1807-1817.
Ronen G, Cohen M, Zamir D and Y Hirschberg (1999) Regulation of carotenoids biosynthesis during tomato fruit development: expression of the gene lycopene epsilon cyclase is down-regulated during ripening and is elevated in the mutant Delta. The Plant Journal 17: 341-352.
Qilin P, Yong-Sheng L, Budai-Hadrian O, Sela M, Carmel-Goren L, Zamir D and R Fluhr (2000) Comparative genetics of NBS-LRR resistance gene homologues in the genomes of two dicotyledons: tomato and Arabidopsis. Genetics 155: 309-322.
Fridman E, Pleban T and D Zamir (2000) A recombination hotspot delimits a wild species QTL for tomato sugar content to 484-bp within an invertase gene. Proc Natl Acad Sci USA 97: 4718-4723.
Ronen G, L Carmel-Goren, D Zamir and J Hirschberg (2000) An alternative pathway to ?-carotene formation in plant chromoplasts discovered by map-based cloning of Beta (B) and old-gold (og) color mutations in tomato. Proc Natl Acad Sci USA 97:11102-7.
Sela M, O Budai-Hadrian, P Qilin, L Carmel-Goren, R Vunsch, D Zamir D and R Fluhr (2001) Genome-wide analysis for Fusarium resistance in tomato reveals multiple complex loci. Mol. Genet. Genomics 265: 1104-1111.
Zamir D. (2001) Improving plant breeding with exotic genetic libraries. Nature Review Genetics 2:983-989.
Fridman, E., Y. S. Liu, L. Carmel-Goren, A. Gur, M. Shoresh, T. Pleban, Y. Eshed and D. Zamir (2002) Two tightly linked QTLs modify tomato sugar content via different physiological pathways. Mol. Genet. Genomics 266: 821-826.
Tadmor Y, Fridman E, Gur A, Larkov O, Ravid U, Zamir D and Lewinsohn E (2002) Identification of malodorous, a wild species allele affecting tomato aroma that was selected against during domestication. J. Agric. Food Chem.50: 2005-2009.
Fridman Eyal and Dani Zamir (2003) Functional divergence of a syntenic gene family in tomato, potato and Arabidopsis. Plant Physiology 131: 603-609.
Liu YS, Gur A, Ronen G, Causse M, Hirschberg J and Zamir D (2003) There is more to tomato fruit color than candidate carotenoid genes. Plant Biotechnology Journal.