MLX56 family defense proteins, MLX56 and its close homolog LA-b, are chitin-binding defense proteins found in mulberry latex that show strong growth-inhibitions against caterpillars when fed at concentrations as low as 0.01%. MLX56 family proteins contain a unique structure with an extensin domain surrounded by two hevein-like chitin-binding domains and have totally unique mode of defensive action against insects. Experimental results suggest that MLX56 family proteins, through their chitin-binding domains, bind to the chitin framework of the peritrophic membrane (PM:a thin membrane consisting of chitin that wraps food materials in the midgut lumen of insects), then through their extensin-domain (gum arabic-like structure), which functions as swelling agent, swells PM into an abnormally thick membrane that inhibits the digestive processes and growth of insects. Plants expressing mlx56 gene (MLX56 protein) showed strong resistances to various pests including Spodoptera litura, Mamestra brassicae, Plutella xylostella (Lepidoptera), and other pests belonging to Coleoptera (ladybirds) and Thysanoptera (thrips), suggesting that MLX56 is a promising substitute of Bt toxin in making pest-resistant plants in future.
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