New insights on the role ofSlDMR6-1in drought avoidance in tomato

Abstract

ABSTRACTThe DOWNY MILDEW RESISTANCE 6 (DMR6) protein is a 2-oxoglutarate (2OG) and Fe(II)-dependent oxygenase, involved in salicylic acid (SA) metabolism, and its inactivation in tomato was found to increase SA levels and to confer disease-resistance against several pathogens. SA is also recognized as an abiotic stress-tolerance enhancer, and we tested the resistance to drought stress inSldmr6-1tomato mutants generated by the CRISPR/Cas9 technique.Wild-type (WT) tomato cultivar ‘San Marzano’ and itsSldmr6-1mutants were subjected to water deprivation for 7 days. At the end of the period, while WT plants exhibited severe wilting, the T2Sldmr6-1mutant plants showed turgid leaves and maintained higher Soil Relative Water Content (SRWC).Sldmr6-1mutants adopted a water saving behaviour reducing transpiration rate (E) by decreasing stomatal conductance (Gs). Assimilation rate (A) decreased in parallel to E under drought stress, resulting in no alteration of the CO2concentration in the sub-stomatal chamber (Ci) and increasing the Water Use Efficiency (WUE, A/E). Defence mechanisms of the photosynthetic machinery triggered inSldmr6-1mutants, that under drought stress showed up-regulation of the genesSlAPXandSlGST(anti-oxidant related) as well as down-regulation ofSlCYP707A2gene, which is involved in ABA catabolism. Our results suggest that the disabling ofSlDMR6-1in tomato plants leads to a drought-avoidance strategy through tight control of stomatal closure controlling water loss. In addition, it was highlighted, for the first time in tomato, thatSldmr6-1mutants showed reduced susceptibility toPhytophthora infestans, the causal agent of Late Blight.