Overexpression of a Rice NPR1 Homolog Leads to Constitutive Activation of Defense Response and Hypersensitivity to Light

Abstract

Arabidopsis NPR1/NIM1 is a key regulator of systemic acquired resistance (SAR), which confers lasting broad-spectrum resistance. Previous reports indicate that rice has a disease-resistance pathway similar to the Arabidopsis SAR pathway. Here we report the isolation and characterization of a rice NPR1 homologue (NH1). Transgenic rice plants overexpressing NH1 (NH1ox) acquire high levels of resistance to Xanthomonas oryzae pv. oryzae. The resistance phenotype is heritable and correlates with the presence of the transgene and reduced bacterial growth. Northern analysis shows that NH1ox rice spontaneously activates defense genes, contrasting with NPR1-overexpressing Arabidopsis, where defense genes are not activated until induction. Wild-type NH1, but not a point mutant corresponding to npr1-1, interacts strongly with the rice transcription factor rTGA2.2 in yeast two-hybrid. Greenhouse-grown NH1ox plants develop lesion-mimic spots on leaves at preflowering stage although no other developmental effects are observed. However, when grown in growth chambers (GCs) under low light, NH1ox plants are dwarfed, indicating elevated sensitivity to light. The GC-grown NH1ox plants show much higher salicylic acid (SA) levels than the wild type, whereas greenhouse-grown NH1ox plants contain lower SA. These results indicate that NH1 may be involved in the regulation of SA in response to environmental changes.

Biosynthesis and emission of insect-induced methyl salicylate and methyl benzoate from rice

“…NH1 appears to have a similar role as NPR1. Overexpression of NH1 in rice led to enhanced resistance to Xanthomonas oryzae [6]. Our data indicate that NH1 is also involved in regulating riceeinsect interactions.…”

“…NH1, which is the ortholog of Arabidopsis NPR1, is an important component of the SA signaling pathway [6]. Previous studies reported that SA-dependent plant defenses in transgenic rice plants overexpressing NH1 gene (NH1ox) were altered [6]. Quantitative real-time PCR was performed to examine expression of OsBSMT1 in NH1ox and LiaoGeng (LG), the wild-type background of NH1ox.…”

“…NH1 lines were produced in the LG background [6]. Rice seeds were dehulled and germinated at 30 C for two days.…”

“…Previous studies indicated that NH1 is a key component of the SA signal transduction pathway in rice. Overexpressing NH1 in rice plants (NH1ox) leads to enhanced resistance to pathogens [6]. In this study, NH1ox plants were studied for understanding the regulatory role of the SA signaling pathway in production of MeSA induced by herbivores.…”

Lessons from the Far End: Caterpillar FRASS-Induced Defenses in Maize, Rice, Cabbage, and Tomato

“…3b). Rice shows a strong SA-JA crosstalk and is known to regulate SA-JA antagonism through non-expresser of pathogenesis-related protein1 (Os-NPR1) that is an early marker for the salicylic acid (SA) pathway and plays a critical role in pathogen defense in rice (Chern et al 2005;Thaler et al 2012;Yuan et al 2007). In addition, overexpression of Os-NPR1 in rice increases its susceptibility to herbivores (Yuan et al 2007).…”