A complete set of alien addition lines, each consisting of 24 L. esculentum chromosomes and 1 chromosome from Solanum lycopersicoides (DeVerna et al., unpublished), has been used to facilitate identification of the interchromosomal locations of several cDNAs representing genes expressed specifically in tomato fruit tissues. These lines have previously been used to rapidly assign tomato genomic clones and isozyme markers to particular chromosomes (Alpert et al., 1989; Alpert, unpublished; Chetelat et al., 1987; Chetelat, 1989). An F2 population (67 individuals) of L. esculentum x L. pennellii was then used to establish intrachromosomal linkage to previously mapped tomato molecular markers (Young and Tanksley, 1989). This two-step mapping strategy is useful when linkage information is limited due to the paucity of F2 linkage data or unavailability of probes which saturate the molecular map.
Three fruit-specific cDNA clones, pectin methylesterase (PMe: Ray et al., 1988; Pear, unpublished), 2A11 (Pear et al., 1989) and pZ130 (Martineau and Houck, unpublished), all mapped to chromosome 7 as shown in figure 1. A fourth cDNA clone expressed in tomato fruit, pZ70 (Martineau and Houck, unpublished) has also been assigned to chromosome 7 and is currently being mapped within the chromosome. All four cDNA clones were identified through differential screening of cDNA libraries prepared from tomato fruit (see, for example, Pear et al., 1989). These cDNA clones are not homologous to one another and have different temporal and spacial patterns of expression within tomato fruit.
Several ripening-related genes have been mapped to different regions of the tomato genome. The gene encoding polygalacturonase, for example, has been mapped to chromosome 10 (Mutschler et al., 1988). Other ripening-related genes have been located on chromosome 5 (pTOM36), chromosome 8 (pTOM92 and pTOM36), chromosome 12 (pTOM13) and chromosome 7 (pTOM4 and pTOM13) (Mutschler et al., 1988).
Fig. 1 Fruit-specific clones PMe, 2A11, and pZ130 were positioned within chromosome 7 using tomato genomic (TG) clones (provided by S. D. Tanksley) and the isozyme, Got-2.
PMe TG20 Got-2 2A11 pZ130 TG61
-----|---|-----------|---|-----------|---------|-----Chromosome
7.3cM 31.8cM 6.9cM 25.0cM 19.4cM 7*
* Recombination frequencies (RF) were calculated using the mapping
program LINKAGE-1 (Suiter, et al., 1983). Recombination frequencies
were then converted to map units in centimorgans (cM) using the
mapping function: 50[-ln(1-2RF)] (Suzuki et al., 1986).Literature cited:
Alpert, K.B., R.T. Chetelat and J.W. DeVerna 1989 Journal of Cellular Biochemistry. UCLA Symposia on Molecular and Cellular Biology. Supplement 13D: 329.
Chetelat, R.T., J.W. DeVerna and C.M. Rick 1987 Tomato Genetics Cooperative Report. 37:39-41.
Chetelat, R.T. 1989 Isozyme bull. 22:19-23.
Mutschler, M., M. Guttieri, S. Kinzer, D. Grierson and G. Tucker 1988 Theor. Appl. Genet. 76:285-292.
Pear, J.R., N. Ridge, R. Rasmussen, R.E. Rose and C.M. Houck 1989 Plant. Molec. Biol. 13:639-651.
Ray, J., J. Knapp, D. Grierson, C Bird. and W. Schuch 1988 Eur. J. Biochem. 174:119-124.
Suiter, K.A., J.F. Wendel and J.S. Case 1983 J. Heredity. 74:203-204.
Suzuki, D.T.,, A.J.F. Griffiths, J.H. Miller and R.C. Lewontin 1986 In: An Introduction to Genetic Analysis. Third edition. p.103-105. W.H. Freeman and Company, New York.
Young, N.D. and S.D. Tanksley 1989 Theor. Appl. Genet. 77:95-101.