High-resolution linkage analysis and physical characterization of the EIX-responding locus in tomato

An ethylene-inducing xylanase (EIX) from Tricohoderma viride is a potent el icitor of ethylene biosynthesis, localized cell death and other defense res ponses in specific cultivars of tobacco (Nicotiana tabacum) and tomato (Lyc opersicon esculentum). Wild species of tomato, such as Lycopersicon cheesma nii and Lycopersicon pennellii, do not respond to EIX treatment. The F-1 pr ogeny of a L. esculentumxL. cheesmanii and a L. esculentumxL. pennellii cro ss responded to EIX treatment with an increase in ethylene biosynthesis and the induction of localized cell death. The F-2 progeny of the above mentio ned crosses segregated 3:1 (responding:non-responding), We mapped the EIX-r esponding locus (Eix) to the short arm of chromosome 7 using a population o f introgression lines (ILs), containing small RFLP-defined chromosome segme nts of L. pennellii introgressed into L, esculentum. RFLP analysis of 990 F -2 plants that segregated for the introgressed segment mapped the fix locus 0.1 cM and 0.9 cM from the flanking markers TG61 and TG131, respectively. Using the marker TG61 we isolated a yeast artificial chromosome (YAC) clone that carries 300-kb DNA segments derived from the fix region. By mapping t he ends of this YAC clone we show that it spans the fix locus. Thus, positi onal cloning of the Eix locus appears feasible.