Engineering disease resistance in rice

Abstract

Rice diseases cause substantial yield loss in rice. Through conventional breeding, resistance genes (R-gene) were transferred into elite rice genotypes particularly against the fungal blast and bacterial blight diseases. Main drawback of this approach is that, in the long term, breakdown of resistance occurs due to evolution of new virulent pathogen strains. In the current scenario, developing rice with durable broad-spectrum resistance through genetic transformation is gaining importance. In this direction, genetic transformation of rice was being carried out for the past two decades via expressing pathogenesis-related (PR) proteins, antimicrobial peptide, and genes governing signaling pathways as well as elicitor proteins. In spite of several reports, the expression of PR proteins and antimicrobial peptides did not yield desirable disease control in rice. Better understanding of disease resistance mechanism in plants helped in identifying critical transcription factors (TFs) involved in disease resistance. Overexpression of NPR1 encoding non-expressor of pathogenesis-related protein 1 and OsWRKY45 transcription factors in rice showed strong disease resistance to multiple pathogens and at the same time resulted in fitness cost. Recently, transgenic rice with high level of resistance to important rice diseases was achieved by expressing NPR1 and WRKY45 under tissue-specific/pathogen-responsive promoter; thereby agronomic traits are not altered. Rice transformants expressing the pathogen-derived elicitor proteins particularly from rice blast pathogen, Magnaporthe oryzae is a promising approach for imparting broad-spectrum disease resistance without yield penalty. Host-delivered RNAi technology is the latest of the approaches toward enhancing disease resistance against sheath blight and viral disease of rice. Recently, genome-editing tools are being deployed in rice to enhance resistance against diseases of rice.