The Arabidopsis AtNPR1 Inversely Modulates Defense Responses Against Fungal, Bacterial, or Viral Pathogens While Conferring Hypersensitivity to Abiotic Stresses in Transgenic Rice

Abstract

The nonexpressor of pathogenesis-related (PR) genes (NPR1) protein plays an important role in mediating defense responses activated by pathogens in Arabidopsis. In rice, a disease-resistance pathway similar to the Arabidopsis NPR1-mediated signaling pathway one has been described. Here, we show that constitutive expression of the Arabidopsis NPR1 (AtNPR1) gene in rice confers resistance against fungal and bacterial pathogens. AtNPR1 exerts its protective effects against fungal pathogens by priming the expression of salicylic acid (SA)-responsive endogenous genes, such as the PR1b, TLP (PR5), PR10, and PBZ1. However, expression of AtNPR1 in rice has negative effects on viral infections. The AtNPR1-expressing rice plants showed a higher susceptibility to infection by the Rice yellow mottle virus (RYMV) which correlated well with a misregulation of RYMV-responsive genes, including expression of the SA-regulated RNA-dependent RNA polymerase 1 gene (OsRDR1). Moreover, AtNPR1 negatively regulates the expression of genes playing a role in the plant response to salt and drought stress (rab21, salT, and dip1), which results in a higher sensitivity of AtNPR1 rice to the two types of abiotic stress. These observations suggest that AtNPR1 has both positive and negative regulatory roles in mediating defense responses against biotic and abiotic stresses.

Salicylic acid and gentisic acid induce RNA silencing-related genes and plant resistance to RNA pathogens

“…Among these, it has been described that RDR1 is induced as a consequence of SA treatments in different plant species (Liu et al, 2009;Quilis et al, 2008;Xie et al, 2001;Yang et al, 2004;Yu et al, 2003). Our results are added to those already described, since they indicate that ToRDR1 is induced as a result of exogenous SA treatments in tomato.…”

“…Among them, NtRdRP activity has been found to increase in tobacco plants following SA treatment (Xie et al, 2001). Orthologous genes of NtRDR1 have been also characterized in other species, such as Nicotiana glutinosa (NgRDR1), N. benthamiana (NbRDR1m), A. thaliana (AtRDR1), Medicago truncatula (MtRDR1) and rice (OsRDR1), being all of them induced by both viral infection and SA treatments (Liu et al, 2009;Quilis et al, 2008;Yang et al, 2004;Yu et al, 2003). Besides, certain viral silencing suppressor proteins also suppress SAmediated defence (Ji and Ding, 2001).…”

uORF-mediated translation allows engineered plant disease resistance without fitness costs

“…We then chose Arabidopsis NPR1 ( AtNPR1 ) 1 , which has been shown to confer broad-spectrum disease resistance in a variety of plants, as the transgene. However, it is known that overexpressing AtNPR1 in rice by the maize ubiquitin promoter caused growth retardation, seed size reduction and development of the so-called lesion mimic disease (LMD) phenotype under certain environmental conditions 14, 22 . To remedy the fitness problem, we expressed the AtNPR1-EGFP fusion gene under the following four regulatory systems: 35S:uorfs TBF1 -AtNPR1-EGFP, 35S:uORFs TBF1 -AtNPR1-EGFP , TBF1p:uorfs TBF1 -AtNPR1-EGFP and TBF1p:uORFs TBF1 -AtNPR1-EGFP .…”

Modulation of host plant immunity by Tobamovirus proteins

“…In Nicotiana tabacum, NtRDR1 activity was found to increase transcriptional levels following SA treatment (Xie et al, 2001). Orthologous genes of NtRDR1 have also been characterized in other species, such as Nicotiana glutinosa (NgRDR1), Nicotiana benthamiana (NbRDR1m), A. thaliana (AtRDR1), Medicago truncatula (MtRDR1) and rice (OsRDR1), all of them being induced by both viral infection and SA treatment (Yu et al, 2003;Yang et al, 2004;Quilis et al, 2008;Liu et al, 2009). Several findings indicate that RDR1 could be involved in the SA-induced resistance against viruses (Alamillo et al, 2006;Lee et al, 2016).…”