Functional analysis of rice NPR1‐like genes reveals that OsNPR1/NH1 is the rice orthologue conferring disease resistance with enhanced herbivore susceptibility†

Abstract

SummaryThe key regulator of salicylic acid (SA)-mediated resistance, NPR1, is functionally conserved in diverse plant species, including rice ( Oryza sativa L.). Investigation in depth is needed to provide an understanding of NPR1 -mediated resistance and a practical strategy for the improvement of disease resistance in the model crop rice. The rice genome contains five NPR1 -like genes. In our study, three rice homologous genes, OsNPR1 / NH1 , OsNPR2 / NH2 and OsNPR3 , were found to be induced by rice bacterial blight Xanthomonas oryzae pv.oryzae and rice blast Magnaporthe grisea , and the defence molecules benzothiadiazole, methyl jasmonate and ethylene. We confirmed that OsNPR1 is the rice orthologue by complementing the Arabidopsis npr1 mutant. Over-expression of OsNPR1 conferred disease resistance to bacterial blight, but also enhanced herbivore susceptibility in transgenic plants. The OsNPR1-green fluorescent protein (GFP) fusion protein was localized in the cytoplasm and moved into the nucleus after redox change. Mutations in its conserved cysteine residues led to the constitutive localization of OsNPR1(2CA)-GFP in the nucleus and also abolished herbivore hypersensitivity in transgenic rice. Different subcellular localizations of OsNPR1 antagonistically regulated SA-and jasmonic acid (JA)-responsive genes, but not SA and JA levels, indicating that OsNPR1 might mediate antagonistic cross-talk between the SA-and JA-dependent pathways in rice. This study demonstrates that rice has evolved an SA-mediated systemic acquired resistance similar to that in Arabidopsis, and also provides a practical approach for the improvement of disease resistance without the penalty of decreased herbivore resistance in rice.

Potential Candidate Genes for Improving Rice Disease Resistance

“…This is a very promising observation showing that the genes used for one pathogen can be used for another. It is noteworthy that the NH1 gene, a key disease pathway regulator, does not seem efficient against blast disease, whereas it confers good levels against blight (Chern et al 2005;Yuan et al 2007).…”

Two Different Banana NPR1-Like Coding Sequences Confer Similar Protection Against Pathogens in Arabidopsis

“…This is due to the ability of NPR1 to activate various forms of antimicrobial Pathogenesis-Related (PR) genes (Cao et al, 1994;Glazebrook et al, 1996;Cao et al, 1997;Yuan et al, 2007;Canet et al, 2010;Shi et al, 2010).…”

“…In Arabidopsis thaliana, in addition to the NPR1 gene, 5 homologous NPR1-like sequences have been identified and characterized (Arabidopsis genome initiative, 2000). Further, Oryza sativa (rice), Medicago trunculata, Poplar trichocarpa (poplar), Vitis vinifera (grape), and Theobroma cocoa (cocoa) harbour 5,4,6,3 and 4 NPR1-like sequences, respectively (Liu et al, 2005;Yuan et al, 2007;Argout et al, 3 2011). Recent phylogenetic analysis has also placed NPR1-like genes into three distinct clades (Bergeault et al, 2010;Argout et al, 2011).…”

Rice RING protein OsBBI1 with E3 ligase activity confers broad-spectrum resistance against Magnaporthe oryzae by modifying the cell wall defence

“…Two R genes, Pi9 and Pi21, confer broad-spectrum resistance against multiple races of M. oryzae [9,10]. Rac GTPasemediated events (e.g., generation of ROS), activation of MAP kinase, and other key components, such as RAR1, SGT1, Hsp90, and WRKY45, play important roles in regulating the immune response against M. oryzae [11][12][13][14][15][16][17][18][19][20][21][22][23][24]. Endogenous SA is involved in defence against M. oryzae [25].…”