A PME-mediated increase of ascorbic acid level affects susceptibility of Solanum lycopersicum to Botrytis cinerea

Solanum lycopersicum, the second most important vegetable crop worldwide, is an important source of antioxidants, such as ascorbic acid (AsA), exhibiting positive effects on human health. One introgression sub-line IL12-4-SL, that shows increased levels of AsA, was previously selected from a Solanum pennellii IL (Introgression Lines) population which consists of 76 lines with different wild chromosomal segments in the genetic background of the cultivated variety M82. The increased level of AsA in IL12-4-SL, compared with M82, was due to the activation of the alternative D-galacturonate pathway related to the up-regulation of the Solyc12g098340 and Solyc12g096730 encoding respectively a pectin methylesterase (PME) and a polygalacturonase (PG). Commercial tomato varieties are highly susceptible to microbial pathogens and in particular to fungal necrotrophs. It is well established that the orchestration of pectic enzymes activity affect plant resistance to pathogens. The aim of this research is to study the responses of the tomato IL12-4-SL line to Botrytis cinerea. B. cinerea, the causal agent of grey mold disease, is a broad-spectrum fungal necrotroph that causes serious pre- and post-harvest rot in more than 200 species worldwide. To identify pectic genes induced in tomato by B.cinerea leaf infection, a bioinformatic-based data mining on the available transcriptomics data was performed. The response of M82 and IL12-4-SL to B.cinerea was evaluated in tomato leaves challenged with the fungal necrotroph. Our results indicate a significant reduced susceptibility of the IL lines to the pathogen. The definition of the molecular bases of the observed plant resistance will provide new insights into the regulatory control of plant resistance by antioxidant accumulation and pectin metabolism and could provide novel tools for obtaining tomato genotypes more resistant to pathogens