Molecular Genetic Analysis of NRR, a Negative Regulator of Disease Resistance

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Systemic acquired resistance (SAR) is induced after a local infection by necrotizing pathogens and renders uninfected parts of the plant resistant to a variety of normally virulent viruses, bacterial and fungi. SAR is associated with the inducible expression of pathogenesis-related (PR) genes. In dicots, the phytohormone salicylic acid (SA) is both necessary and sufficient for the induction of SAR. The NPR1 protein is a key regulator of SA-mediated SAR in Arabidopsis. npr1 mutants fail to express SAR related PR genes and display enhanced susceptibility to pathogen infection even after treatment with SA. Furthermore, over-expression of NPR1 in Arabidopsis leads to enhanced disease resistance to both bacterial and fungal pathogens in a dose-dependent manner. We have now shown that over-expression of NPR1 in rice leads to enhanced resistance to the bacterial pathogen Xanthomonas oryzae pv. oryzae (Xoo), a serious disease of rice throughout the world. In addition, we have isolated three resistance signaling components from rice: a rice NPR1 homolog, NH1, and two genes that encode products that interact with NH1 and NPR1; a bZIP transcription factor, rTGA2.1, and a previously unidentified signaling component, NRR (Negative Regulator of disease Resistance).The long-term goal of this proposal is to further elucidate the signal cascade governing plant disease resistance and to create novel strategies for disease control in rice and other cereal crops.