Promoter analysis of pathogenesis-related genes in resistant and susceptible tomato cultivars ans Lycopersicon wild species

Genomes are known to contain coding, but also non-coding sequences, considered for a long time "junk DNA" devoid of any biological meaning. The discovery of a large array of regulatory functions has changed this view, and led to a new attention to the features of upstream, intervening and downstream DNA tracts. Here we report the first part of a study on the correlation between variations in non-coding DNA sequences, i.e. promoters, and the level of gene expression in genes coding for pathogenesis-related (PR) proteins, known to play a crucial role in host-pathogen interaction both at the local and the systemic level, with the aim of developing markers for tolerance/resistance to disease. Promoters of PR-genes have been shown to contain sequences involved in the induction of gene expression upon wounding and after treatment with ethylene, methyl jasmonate, salicylic acid or other elicitors, such as the PR- or GCC- box. Based on these data, we have chosen two genes whose promoters contain one or more GCC boxes, i.e. endochitinase and osmotin, and the gene coding for the PR1a2 protein. The study has been carried out on 14 Lycopersicon esculentum cultivars susceptible or resistant to pathogens, and on the wild species L. pennellii, L. pimpinellifolium, L. peruvianum and L. minutum. Promoter sequences have been amplified by PCR, cloned and sequenced. The sequences thus obtained have been aligned, and parameters related to gene expression (variations in cis-acting regulatory elements, bendability, curvature propensity) have been evaluated. Preliminary data show that single nucleotide polymorphisms, variations in microsatellite length and in the bendability/curvature propensity plots can be detected, the sequences of the wild species showing the highest variability.