Constitutive expression of Arabidopsis NPR1 confers enhanced resistance to the early instars of Spodoptera litura in transgenic tobacco

Abstract

In Arabidopsis, NPR1 (AtNPR1) regulates salicylic acid (SA)-mediated activation of PR genes at the onset of systemic acquired resistance. AtNPR1 also modulates SA-induced suppression of jasmonic acid-responsive gene expression, and npr1 mutants manifest enhanced herbivore resistance. We have raised stable transgenic tobacco lines, expressing AtNPR1 constitutively, which showed elevated expression of PR1 and PR2 genes upon SA treatment. Herbivore bioassays with a generalist polyphagous pest, Spodoptera litura, revealed that the transgenic lines exhibited enhanced resistance compared to the wild-type plants, particularly with respect to younger larval populations. Insect-mediated injury induced several protease inhibitors (PIs), more significantly a 40-kDa serine PI in all the tobacco lines, but the induction was higher in the transgenic plants. We show in this communication that heterologous expression of AtNPR1 provides enhanced resistance to early larval populations of the herbivore, Spodoptera in transgenic tobacco plants.

Broad-spectrum disease resistance to necrotrophic and biotrophic pathogens in transgenic carrots (Daucus carota L.) expressing an Arabidopsis NPR1 gene

“…Similarly, tomato plants expressing AtNPR1 exhibited constitutive induction of many PR genes, including PR-1, PR-2 and PR-4 in a dose-dependent manner relative to the level of AtNPR1 present in the transgenic line (Lin et al 2004 fact that there were several PR genes that were constitutively upregulated in the transgenic tomato plants, there were no deleterious phenotypes or reduction in plant vigor observed (Lin et al 2004). Wheat plants expressing AtNPR1 had no constitutive increase in PR-1 gene expression (Makandar et al 2006), whereas tobacco plants exhibited similar increases in PR-1 induction to that of the tomato plants (Meur et al 2008). There were no reported deleterious phenotypes in either the transgenic wheat or tobacco, with the wheat exhibiting a signiWcant increase in seed yield (Makandar et al 2006).…”

“…The enhanced defense gene response was similar to that seen in Arabidopsis plants overexpressing AtNPR1, where the transgenic plants became increasingly sensitive to the SA analog BTH, resulting in higher production of PR-1 (Friedrich et al 2001). Heterologous AtNPR1 can maintain functionality by interacting with PR gene transcription factors in other plant species (Chern et al 2001;Lin et al 2004;Makandar et al 2006;Meur et al 2008), indicating a relatively high level of evolutionary conservation within the gene. The protein similarities are seen in the characterized NPR1-like enzymes identiWed from apple (Malnoy et al 2007), Brassica juncea (Meur et al 2006), rice (Chern et al 2005;Yuan et al 2007) and banana (Endah et al 2008) indicating a large degree of functional overlap.…”

“…Nuclear NPR1 interacts with TGA family of basic leucine zipper transcription factors, which in turn induce expression of several PR genes (Subramaniam et al 2001;Fan and Dong 2002). Functionality of AtNPR1 remains active in diVerent plant species and has led to pathogen and SA-induced increases in PR gene expression in transgenic rice (Fitzgerald et al 2004;Quilis et al 2008), wheat (Makandar et al 2006), tobacco (Meur et al 2008) and tomato (Lin et al 2004). This indicates that AtNPR1 when expressed in a heterologous system reacts in a similar fashion to the endogenous NPR1-like proteins.…”

“…This indicates that AtNPR1 when expressed in a heterologous system reacts in a similar fashion to the endogenous NPR1-like proteins. The plants constitutively expressing AtNPR1 have shown resistance to both necrotrophic (Lin et al 2004;Makandar et al 2006) and biotrophic fungal, viral and bacterial pathogens (Lin et al 2004) in addition to insect pests (Meur et al 2008).…”

Salicylic Acid and Defense Responses in Plants

“…Since then transgenic studies using NPR1 or its orthologs from other species have been extended to a large group of crop plants for resistance against pathogens with either biotrophic or necrotrophic lifestyle (Tables 1 and 2 ). In addition, overexpression of NPR1 seems to enhance resistance to insect and root-knot nematode in tobacco plants (Meur et al 2008 ;Priya et al 2011 ). Interestingly, the majority of the transgenic plants display little or no constitutive expression of PR genes; rather, the transgenic plants exhibit a "primed" phenotype where induction of PR genes is faster, at higher intensity, and for a longer duration, resulting in a heightened capacity to undergo SAR when challenged with pathogens or treated with SA analogs.…”