Knockout of a pectate lyase in tomato increases fruit firmness and reduces foliar susceptibility to pathogens

As agriculture and food systems are facing growing challenges because of extreme weather conditions and unstable socioeconomic landscapes, improving crop quality and agronomic traits has become an increasingly important goal in plant breeding. Preventing post-harvest losses and finding new genetic sources for pathogen resistance are vital for the development of resilient and competitive varieties. In tomato (Solanum lycopersicum L.), fruit softening plays a key role in determining the post-harvest quality, with a significant impact on both food waste and food safety. To elucidate the role of pectate lyase (SlPL, Solyc03g111690) in the softening process and in susceptibility-to-pathogen mechanisms, knock-out mutants have been generated in a Micro-Tom genetic background by CRISPR/Cas9. Two CAS-free edited mutant lines (carrying a 1 bp insertion and a 2 bp deletion, respectively) showed a significant increase in fruit firmness at two different ripening stages (breaker+4 and red ripe) and lower weight loss during post-harvest storage. Furthermore, the observed overall reduction in the activity of six cell wall remodeling enzymes (pectate lyase, pectin methylesterase, polygalacturonase, α-D-galactosidase, ꞵ-D-galactosidase and ꞵ-D-glucosidase) and the reduced susceptibility to leaf infection caused by Botrytis cinerea, Phytophthora capsici and Pseudomonas syringae pv. tomato pathogens suggested that the alteration of the cell wall metabolism limits the pathogen's ability to establish infection. The obtained results open the possibility of developing new tomato varieties that meet both agronomic and quality needs while helping to clarify the complexity of the cell wall-disassembly process.