Putative pathogenesis-related genes within Solanum nigrum L. var. americanum genome: isolation of two genes coding for PR5-like proteins, phylogenetic and sequence analysis

Pathogenesis-related (PR) proteins are involved in plant responses to biotic and abiotic stress and are grouped into 14 families (PR-1–PR-14). Two PR5-like genes were isolated from black nightshade ( Solanum nigrum L. var. americanum) genome, a solanaceous weed. A complete open reading frame consisting of 744 bp, coding for a precursor of a neutral PR5-like protein, and a DNA fragment of 621 bp long, coding for another basic PR5-like protein, were obtained by using PCR amplification. Based on sequence comparisons with tobacco osmotin and osmotin-like proteins (OLPs), members of the antifungal PR-5 family, these proteins were named SnOLP (neutral) and SnOSML (basic). The two predicted mature proteins are 207 amino acids in length and contain the 16 cysteine residues involved in the eight disulfide bonds common to most PR-5 proteins. Southern blot analysis revealed that osmotin-like proteins are encoded by at least eight members of a multigene family in S. nigrum. This is the first report of the isolation of PR5-like genes from the S. nigrum genome. Computer modeling of the new sequences produces structures that, according to current hypotheses, are indicative of antifungal activity. Phylogenetic analysis of solanaceous PR-5 proteins was also carried out revealing three major groups with different characteristics.