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, 44 (2), 245-57

Regulation of Plant Defense Responses in Arabidopsis by EDR2, a PH and START Domain-Containing Protein

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Regulation of Plant Defense Responses in Arabidopsis by EDR2, a PH and START Domain-Containing Protein

Dingzhong Tang et al. Plant J.

Erratum in

  • Plant J. 2006 Jul;47(1):163

Abstract

We have identified an Arabidopsis mutant that displays enhanced disease resistance (edr2) to the biotrophic powdery mildew pathogen Erysiphe cichoracearum. Inhibition of fungal growth on edr2 mutant leaves occurred at a late stage of the infection process and coincided with formation of necrotic lesions approximately 5 days after inoculation. Double-mutant analysis revealed that edr2-mediated resistance is suppressed by mutations that inhibit salicylic acid (SA)-induced defense signaling, including npr1, pad4 and sid2, demonstrating that edr2-mediated disease resistance is dependent on SA. However, edr2 showed normal responses to the bacterial pathogen Pseudomonas syringae pv. tomato strain DC3000. EDR2 appears to be constitutively transcribed in all tissues and organs and encodes a novel protein, consisting of a putative pleckstrin homology (PH) domain and a steroidogenic acute regulatory protein-related lipid-transfer (START) domain, and contains an N-terminal mitochondrial targeting sequence. The PH and START domains are implicated in lipid binding, suggesting that EDR2 may provide a link between lipid signaling and activation of programmed cell death mediated by mitochondria.

Figures

Figure 1
Figure 1
Response of Arabidopsis WT and edr2 mutant plants to E. cichoracearum. (a) Col-0 and edr2 plants were inoculated with E. cichoracearum and leaves detached for photography 8 days after inoculation. (b) Fungal hyphae growing on the surface of Col-0 leaves 5 days after infection, stained with trypan blue. (c) Fungal hyphae growing on the surface of the edr2 mutant leaves 5 days after infection. Mesophyll cell death (arrow) is apparent at this stage. (d) Extensive conidia (arrow) produced on Col-0 leaves 7 days after infection. (e) Extensive mesophyll cell death (arrow) in edr2 mutant leaves 7 days after infection, but very few conidia.
Figure 2
Figure 2
PR-1 transcripts accumulate more rapidly in the edr2 mutant than in WT plants after infection with E. cichoracearum. Top: an RNA gel-blot hybridized with a radiolabeled PR-1 cDNA probe. Bottom: the corresponding ethidium bromide-stained gel to show the relative amounts of RNA loaded in each lane.
Figure 3
Figure 3
Resistance to powdery mildew mediated by the edr2 mutation is dependent on SA signaling, but not JA or ethylene signaling. The indicated mutants were inoculated with E. cichoracearum and disease phenotypes scored 8 days after infection. Single representative leaves were removed from intact plants for photography.
Figure 4
Figure 4
Enhanced ethylene-induced senescence in edr1 and edr2 mutant plants. (a) Increased chlorosis after ethylene treatment. Plants were photographed after 3 days of exposure to 100 μl l−1 ethylene. (b) The chlorophyll content in leaves five to eight (leaf one being the first true leaf) of the plants shown in (a). Bars represent the mean and standard deviation of values obtained from four plants.
Figure 5
Figure 5
Positional cloning of the EDR2 gene. (a) Genetic and physical map of the region flanking EDR2. Shorter horizontal lines indicate BAC clones spanning the region to which edr2 was mapped. (b) Complementation of the edr2 mutation by Agrobacterium-mediated transformation. The indicated plants were inoculated with E. cichoracearum and representative leaves removed for photography 8 days after inoculation. Both a genomic cosmid clone (#3) and a cDNA clone (35S EDR2) containing the At4g19040 gene were able to complement the mutation.
Figure 6
Figure 6
Characterization of EDR2. (a) Structure of the EDR2 gene. Insertion sites in the Salk T-DNA lines are indicated by arrows. Numbers in parentheses indicate the nucleotide position in the genomic sequence relative to the start of the coding region. (b) The predicted EDR2 protein contains 718 amino acids and includes a PH domain, a START domain and a C-terminal DUF1336 domain, which is highly conserved among homologs in other plant species. (c) Alignment of the EDR2 C-terminal DUF1336 domain with the most similar Arabidopsis protein (At5g44560) and homologs from other plant species identified in the TIGR Plant Gene Indices database. Tentative consensus numbers for the homologs are Oryza sativa (rice), TC251404; Saccharum officinarum (sugarcane), TC58737; Hordeum vulgare (barley), TC150750; Lycopersicon esculentum (tomato), TC144758; Medicago truncatula (medicago), TC88033; Lotus japonicus (lotus), TC15086.
Figure 7
Figure 7
EDR2 is expressed in all tissues and organs examined. EDR2 promoter–GUS expression in (a) seedlings, (b) roots, (c) stem, (d) flower and (e) silique.

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