Significance of Cuscutain, a cysteine protease from Cuscuta reflexa, in host-parasite interactions

One of the infestation specific Cuscuta genes encodes a cysteine protease. The protein and its intrinsic inhibitory peptide were heterologously expressed, purified and biochemically characterized. The haustoria specific enzyme was named cuscutain in accordance with similar proteins from other plants, e.g. papaya. The role of cuscutain and its inhibitor during the host parasite interaction was studied by external application of an inhibitor suspension, which induced a significant reduction of successful infection events.The study provides new information about molecular events during the parasitic plant - host interaction. Inhibition of cuscutain cysteine proteinase could provide means for antagonizing parasitic plants.Parasitic weeds such as Cuscuta reflexa are obligate holoparasites with low host specificity. The plants are found in areas with relatively mild climates around the world. In farming regions, these parasites cause substantial damage to many commercially important crops such as sugar beet, alfalfa, pepper, cucumber, tomato potato or allium [1]. Currently, an effective control of Cuscuta outbreaks is based on preventive strategies including control of seed contamination and application of herbicides prior to seed emergence. The use of herbicides on infected plants with an established host parasite interaction only appears to be successful and not harmful to the host plant if the host is herbicide resistant [2,3]. Due to difficulties with conventional breeding techniques, molecular biology genomic research on parasites is needed to develop new control strategies [4-8]. Research on host reactions to parasitic plant infection in model plants such as Arabidopsis thaliana, Medicago truncatula and crops like tomato or tobacco have already generated promising results [9-12].In Cuscuta spp. photosynthesis is reduced or absent [13]. Consequently, the plant depends on carbohydrates withdrawn from the host plant [14]. A connection (haustorium) at the contact site i