Tomato Plants Overexpressing a Celery Mannitol Dehydrogenase (MTD) Have Decreased Susceptibility to Botrytis cinerea

The oxidative burst is a critical early event in plant-pathogen interactions that leads to a localized, programmed cell death (PCD) called the hypersensitive response (HR). The HR and associated PCD retard infection by biotrophic pathogens, but can, in fact, enhance infection by necrotrophic pathogens like Botrytis cinerea. In addition to signaling the induction of the HR, reactive oxygen species (ROS) produced during the oxidative burst are antimicrobial. The authors hypothesize that pathogens such as B. cinerea survive the antimicrobial effects of ROS, at least partially by secreting the antioxidant mannitol during infection. This is supported by the previous observation that overexpression of the catabolic enzyme mannitol dehydrogenase (MTD) can decrease a plants susceptibility to mannitol-secreting pathogens like B. cinerea. To extend the above hypothesis, and test the general utility of this approach in an important horticultural crop, we overexpressed celery MTD in tomato. In these studies, they observed a significant increase (up to 90%) in resistance to B. cinerea in transgenic tomatoes expressing high amounts of MTD.