Innate Immunity in Rice: A Defense Against Bacterial Leaf Blight

Rice (Oryza sativa L.) is one of the major staple food crops of the world and sustainable rice production is important for ensuring global food security. Throughout the growing season, a variety of pathogens including fungi, bacteria, viruses, and nematodes, infect different parts of the crop resulting in yield loss. Bacterial leaf blight caused by Xanthomonas oryzae pv. oryzae (Xoo) is one of the major limiting factors in rice production. Being a vascular pathogen, X. oryzae pv. oryzae interferes with a range of physiological and biochemical exchange process in rice. The earlier the pathogen infection, more will be the loss and grain quality is also severely affected due to infection. The spread of the pathogen is too rapid in the favourable climatic conditions. The disease results in 20 to 30 per cent annual loss in rice production and under severe conditions, the yield loss goes up to 80 per cent. Plant pathogens employ different ways to attack host plants and impair plant growth and reproduction. Unlike vertebrates, plants lack mobile immune cells and an adaptive immune system. Plants mainly rely on two interconnected tiers of the innate immune system to perceive and respond to pathogen infection. This innate immune system or basal resistance mediated by a repertoire of Resistance or R genes in plants acts as the first line of pre-formed and inducible defenses that protect the host plants from large number of pathogens. Over the years, extensive investigation on the molecular interactions between rice and Xanthomonas oryzae pv. oryzae has made impressive progress in understanding the molecular basis of rice innate immunity against bacterial leaf blight. Improving plant immunity has been considered as one of the best choices available for achieving economical and sustainable management of bacterial leaf blight in a durable manner. In this review, we summarize the molecular basis of two tiered innate immune system including PAMP triggered immunity (PTI) and Effector triggered immunity (ETI) as well as R genes involved in rice - Xanthomonas oryzae pv. oryzae interaction.