The Arabidopsis Downy Mildew Resistance Gene RPP8 Is Induced by Pathogens and Salicylic Acid and Is Regulated by W Box cis Elements

Abstract

Plants disease resistance (R) genes encode specialized receptors that are quantitative, rate-limiting defense regulators. R genes must be expressed at optimum levels to function properly. If expression is too low, downstream defense responses are not activated efficiently. Conversely, overexpression of R genes can trigger autoactivation of defenses with deleterious consequences for the plant. Little is known about R gene regulation, particularly under defense-inducing conditions. We examined regulation of the Arabidopsis thaliana gene RPP8 (resistance to Hyaloperonospora arabidopsidis, isolate Emco5). RPP8 was induced in response to challenge with H. arabidopsidis or application of salicylic acid, as shown with RPP8-Luciferase transgenic plants and quantitative reverse-transcription polymerase chain reaction of endogenous alleles. The RPP1 and RPP4 genes were also induced by H. arabidopsidis and salicylic acid, suggesting that some RPP genes are subject to feedback amplification. The RPP8 promoter contains three W box cis elements. Site-directed mutagenesis of all three W boxes greatly diminished RPP8 basal expression, inducibility, and resistance in transgenic plants. Motif searches indicated that the W box is the only known cis element that is statistically overrepresented in Arabidopsis nucleotide-binding leucine-rich repeat promoters. These results indicate that WRKY transcription factors can regulate expression of surveillance genes at the top of the defense-signaling cascade.

Genome-Wide Identification and Expression Analysis of NBS-Encoding Genes in Malus x domestica and Expansion of NBS Genes Family in Rosaceae

“…Further, over-expression of a pepper NBS-LRR gene, Bs2 in transgenic tomato conferred increased resistance against bacterial spot disease along with substantial increase in yield [50]. Similarly, higher expression of downy mildew resistance gene RPP8 in Arabidopsis was reported by Mohr et al [51] in response to Hyaloperonospora arabidopsidis and salicylic acid.…”

A Role for Nonsense-Mediated mRNA Decay in Plants: Pathogen Responses Are Induced in Arabidopsis thaliana NMD Mutants

“…The phenotype of the NMD mutants mimics that of other Arabidopsis lines that overexpress pathogen responsive genes, including plants in which R genes are constitutively active [77], [78]. As activation of numerous R genes causes SA accumulation and numerous R genes are up-regulated in response to SA [79], [80], it is difficult to conclude whether individual NMD repressed genes are direct or indirect targets of NMD. To understand this further requires the identification of transcripts that are direct targets of plant NMD.…”

Role of Intron-Mediated Enhancement on Accumulation of an Arabidopsis NB-LRR Class R-protein that Confers Resistance to Cucumber mosaic virus

“…The expression of a limited number of these genes can be induced by the bacterial flagellin peptide, flg22 or by salicylic acid (SA) treatment [9]. However, significant induction of known R gene expression during the plant defense response seems to occur only in a minority of the cases examined so far [9]–[15]. The transcript levels of other R genes do not change in response to pathogen attack [16]–[19].…”

“…The transcript levels of other R genes do not change in response to pathogen attack [16]–[19]. Furthermore, global expression analysis of NB-LRR-encoding and related genes in Arabidopsis suggests that most NB-LRR-encoding genes tend to be more responsive to pathogens than randomly selected genes, but less responsive to pathogens than common defense-related marker genes [9], [15]. Therefore, in general, R genes may not generally need to be induced at the transcriptional level to regulate resistance to pathogens.…”