(TG clones) common to the map constructed by Tanksley et al. (1992). To position the Lemmi genes on the genetic
map, we have hybridized each to Southern blots containing DNA, digested with Dra I, from the 84 plants of our
mapping population and added the segregation data to the linkage data for this population, using the JoinMap
computer program (Stam, 1993).
The linkage analysis showed that Lemmi 9 is located on chromosome 1 between the markers TG71 and
TG209 and that Lemmi 2 and Lemmi 10 map to the same position at the end on chromosome 10 below the marker
TG420 (fig.1). In fact, Lemmi 2 and Lemmi 10 both hybridized to a 1.2kb Dral fragment. To refine the map positions
of Lemmi genes on chromosomes 1 and 10, we have scored in our mapping population the segregation of two
additional RFLP markers, TG 295 and TG 229, that are known from the published map (Tanksley et al., 1992) to be
at close distance to Lemmi 9 and Lemmi 2 (Lemmi 10, respectively.
As shown in fig.1 the nematode-induced Lemmi 9 gene maps between TG71 and TG295. Comparison with
the Tanksley map shows that Lemmi 9 is located near the previously mapped ACC2 gene, which is induced in
tomato during floral and fruit senescence (Rottmann et al., 1991). Lemmi 2 and Lemmi 10 genes, which cross-
hybridize but show different expression patterns, probably represent two members of a gene family that are
physically linked on a Dra I fragment of 1.2 kb.
To be able to draw a more general picture of how functionally related genes, like the nematode-induced
ones, are distributed over the chromosomes, more genes need to be identified and mapped.
Acknowledgments
This research was supported in part by a grant (no.Cl 1-CT91-0932) from the Commission of the European
Communities.
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