Integrative analysis of pectin methylesterase (PME) and PME inhibitors in tomato (Solanum lycopersicum): Identification, tissue-specific expression, and biochemical characterization.

Although previous studies have demonstrated that the degree of demethylesterification of pectin polysaccharides is modulated during tomato fruit ripening, its involvement in vegetative organ development has been seldom investigated. As a first step in understanding the importance of pectin modification during vegetative stages, we used chemical, biochemical, and molecular approaches to analyze PMEs and PMEIs in tomato plants. We found that tomato cell walls isolated from vegetative tissues as well as the fruit contain substantial quantities of pectin, and different degrees of methylesterification were evident in different tissues. Our chemical study was further substantiated by immunolocalization analysis, which showed that selective removal of pectin-bound methyl groups is required for proper organ development and growth. In the tomato genome, there exists 79 PMEs and 48 PMEIs with temporally and spatially regulated expression. As a case study, we showed that two tomato PMEIs (SolycPMEI13 and SolycPMEI14) exhibited PMEI activities. This is the first report regarding the genome-wide identification and expression profiling of PME/PMEIs in tomato and the first chemical evidence of the differential degrees of pectin methylesterification in vegetative and reproductive tissues. Taken together, our findings provide an important tool to unravel the molecular and physiological functions of tomato PME and PMEI in further study.