Analysis of Resistance Gene-Mediated Defense Responses in Arabidopsis thaliana Plants Carrying a Mutation in CPR5

Abstract

In resistant plants, pathogen attack often leads to rapid activation of defense responses that limit multiplication and spread of the pathogen. To investigate the signaling mechanisms underlying this process, we carried out a screen for mutants in the signaling pathway governing resistance in Arabidopsis thaliana to the bacterial pathogen Pseudomonas syringae. This involved screening for suppressor mutations that restored resistance to a susceptible line carrying a mutation in the RPS2 resistance gene. A mutant that conferred resistance by activating defense responses in the absence of pathogens was isolated. This mutant, which carries a mutation at the CPR5 locus and was thus designated cpr5-2, exhibited resistance to P. syringae, spontaneous development of necrotic lesions, elevated PR gene expression in the absence of pathogens, and abnormal trichomes. Resistance gene-mediated defenses, including the hypersensitive response, restriction of pathogen growth, and induction of defense-related gene expression, were functional in cpr5-2 mutant plants. Additionally, in cpr5-2 plants RPS2-mediated induction of PR-1 expression was enhanced, whereas RPM1-mediated induction of ELI3 was not. These findings suggest that CPR5 encodes a negative regulator of the RPS2 signal transduc-tion pathway.

Constitutive disease resistance requires EDS1 in the Arabidopsis mutants cpr1 and cpr6 and is partially EDS1‐dependent in cpr5

“…Effect of eds1 on defense-related gene expression in the cpr mutants cpr1, cpr5 and cpr6 plants constitutively express the PR genes PR1, PR2 (BGL-2) and PR5, which are markers for SAR (Boch et al, 1998;, Bowling et al, 1997Clarke et al, 1998). Also, cpr5 and cpr6 induce expression of PDF1.2 mRNA, a marker of JA/ET-dependent signaling.…”

“…The pleiotropic nature of cpr5 suggests a complex interplay of signals that undoubtedly complicates genetic epistasis studies (Boch et al, 1998;Bowling et al, 1997). We found that initiation of lesions (Figure 2a), pathogen resistance ( Figure 4) and SA accumulation ( Figure 5) in cpr5 eds1 plants resembles that in cpr5 or cpr5 EDS1 lines.…”

“…In contrast to npr1, the recessive cpr1 and cpr5 (constitutive expressor of PR genes) and dominant cpr6 mutants activate SAR responses, enhancing resistance to virulent isolates of the bacterial pathogen Pseudomonas syringae ES4326 and the oomycete pathogen Peronospora parasitica Noco2 , Bowling et al, 1997Clarke et al, 1998). cpr5 also forms spontaneous lesions in the absence of pathogens, and has abnormal trichomes (Boch et al, 1998;Bowling et al, 1997). The cpr mutants interfere with plant defense signaling at different points along the SAR cascade.…”

CPR5, a Jack of all trades in plants

“…The gene was initially identified in screens for mutants with enhanced disease resistance. 2,3 Several more cpr5 alleles were subsequently identified in screens for mutants with altered trichome development, 4 dark induced senescence (hys1 alleles) 5 and ethyleneinduced senescence (old1 alleles). 1,6 So far, described alterations in cpr5 mutants include (1) enhanced constitutive expression of PR genes, (2) elevated salicylic acid and jasmonic acid levels, (3) hypersensitivities to sugar, ABA, ethylene and jasmonic acid, (4) accelerated leaf senescence, (5) spontaneous lesion mimic cell death, (6) defective cell proliferation, endoreduplication and trichome development, (7) reduced plant growth and reproduction fecundity.…”

“…1,6 So far, described alterations in cpr5 mutants include (1) enhanced constitutive expression of PR genes, (2) elevated salicylic acid and jasmonic acid levels, (3) hypersensitivities to sugar, ABA, ethylene and jasmonic acid, (4) accelerated leaf senescence, (5) spontaneous lesion mimic cell death, (6) defective cell proliferation, endoreduplication and trichome development, (7) reduced plant growth and reproduction fecundity. [1][2][3][4][5][6][7] Thus, cpr5 mutations possess pleiotropic phenotypes indicating that CPR5 is an essential-for-life gene in Arabidopsis.…”