Expression of Harpin_Xoo in Transgenic Tobacco Induces Pathogen Defense in the Absence of Hypersensitive Cell Death

Abstract

Harpin(Xoo), encoded by the hpaG(Xoo) gene of Xanthomonas oryzae pv. oryzae, is a member of the harpin group of proteins that induce pathogen resistance and hypersensitive cell death (HCD) in plants. We elaborated whether both processes are correlated in hpaG(Xoo)-expressing tobacco (HARTOB) plants, which produced harpin(Xoo) intracellularly. Resistance to fungal, bacterial, and viral pathogens increased in HARTOB, in correlation with the expression of hpaG(Xoo), the gene NPR1 that regulates several resistance pathways, and defense genes GST1, Chia5, PR-1a, and PR-1b that are mediated by different signals. However, reactive oxygen intermediate burst, the expression of HCD marker genes hsr203 and hin1, and cell death did not occur spontaneously in HARTOB, though they did in untransformed and HARTOB plants treated exogenously with harpin(Xoo). Thus, the transgenic expression of harpin(Xoo) confers nonspecific pathogen defense in the absence of HCD.

Tobacco TTG2 Quells Resistance to Pathogens by Sequestering NPR1 from Nuclear Localisation

“…RT-PCT and real-time RT-PCR were conducted using specific primers (supplementary material Table S2) and previously described protocols (Chen et al, 2008;Liu et al, 2010). The stably expressed EF1a or ACTIN2 gene (Wu et al, 2010;Peng et al, 2004;Liu et al, 2011;Dong et al, 2004;Dong et al, 2005) was used as a reference. Gene expression levels were quantified as described (Livak and Schmittgen, 2001).…”

Nicotiana tabacumTTG1 contributes to ParA1-induced signalling and cell death in leaf trichomes

“…3D). In leaf trichomes, HCD marker genes PAL1, hin1 and hsr203 Peng et al, 2003;Peng et al, 2004) were expressed strongly from 3 hpt with ParA1 (Fig. 3E), whereas mesophylls were inferior to trichomes in time and extent of the gene expression (Fig.…”

“…To our knowledge, causal relationships between ROS and cell death and between cell death and plant defence against pathogens remain an issue with broad importance. In both plants under infection by pathogens (Jabs et al, 1996;Tanaka et al, 2003) or those treated with different elicitors (Desikan et al, 1998;Peng et al, 2003;Peng et al, 2004;Tanaka et al, 2003;Trouvelot et al, 2008), ROS production is either dispensable for the induction of cell death and indispensable for the defence response. This is true for elicitins based on published studies.…”

“…The RFP gene used to construct NtTTG1-RFP was cloned from the vector pDsRed2-1 (Clontech); primers were 5Ј-CGGGAATTCATGGCCTCCTCCGAG -AACGTC-3Ј, 5Ј-CGGGTCGACCTACAGGAACAGGTGGTGGCGG-3Ј; bold and underlined letters are EcoRI and SalI restriction sites, respectively. Regular protocols Peng et al, 2004) were used in gene recombination.…”

“…In response to an elicitor, HCD develops as a microscopic hypersensitive response (micro-HR) with or without subsequent emergence of macroscopic HR (macro-HR). Micro-HR is induced more frequently than macro-HR Peng et al, 2004;Takemoto et al, 2005) and is required for macro-HR to be further induced (Peng et al, 2003). Both types of HCD occur as a result of intracellular transduction of reactive oxygen species (ROS) signals, such as hydrogen peroxide (H 2 O 2 ), O 2 · -, and hydroxyl radicals (Blokhina et al, 2003;Torres et al, 2006;Sagi and Fluhr, 2006).…”