Despite the use of chemical fungicides,
fungal diseases have a major impact on the yield and quality of plant produce globally and hence there is a need for new approaches for disease control. Several groups have examined the potential use of antifungal plant
defensins for plant protection and have produced transgenic plants expressing plant
defensins with enhanced resistance to
fungal disease. However, before they can be developed commercially, transgenic plants must pass a series of strict regulations to ensure that they are safe for human and animal consumption as well as the environment. One of the requirements is rapid digestion of the transgene
protein in the gastrointestinal tract to minimize the risk of any potential allergic response. Here, we examine the digestibility of two plant
defensins, NaD1 from Nicotiana alata and SBI6 from soybean, which have potent antifungal activity against major cereal pathogens. The native
defensins were not digestible in simulated gastrointestinal fluid assays. Several modifications to the sequences enhanced the digestibility of the two small
proteins without severely impacting their antifungal activity. However, these modified
proteins did not accumulate as well as the native
proteins when transiently expressed in planta, suggesting that the
protease-resistant structure of plant
defensins facilitates their stability in planta.