A Brassica juncea chitinase with two-chitin binding domains show anti-microbial properties against phytopathogens and Gram-negative bacteria.

In our recent paper in the Journal of Experimental Botany, we demonstrated that Brassica juncea BjCHI1 shows anti-fungal properties against phytopathogens, Colletotrichum truncatum, C. acutatum, Botrytis cinerea and Ascochyta rabiei. Furthermore, BjCHI1 which is an unusual plant chitinase with two (almost identical) chitin-binding domains, agglutinates Gram-negative bacteria, adversely affecting their growth. In contrast, BjCHI1 derivatives lacking one or both domains do not show agglutination activity, suggesting that both chitin-binding domains are essential for agglutination. Observations that agglutination could be relieved by addition of galactose, glucose or lactose, imply that BjCHI1 interacts with the carbohydrate components of the Gram-negative bacterial cell wall. We propose here, a model for BjCHI1-mediated agglutination between Gram-negative bacteria, through interaction of their adjacent cell walls mediated by the two chitin-binding domains of BjCHI1. BjCHI1 is a plant chitinase which has evolved towards acquiring an enhanced role in plant defense against fungi and Gram-negative bacteria. Hence, it is a promising candidate for applications against phytopathogens in plant genetic engineering via nuclear or plastid transformation.