Abstract
Plants have been shown previously to perceive bacteria on the leaf surface and respond by closing their stomata. The virulent bacterial pathogen Pseudomonas syringae pv tomato DC3000 (PstDC3000) responds by secreting a virulence factor, coronatine, which blocks the functioning of guard cells and forces stomata to reopen. After it is inside the leaf, PstDC3000 has been shown to up-regulate abscisic acid (ABA) signaling and thereby suppress salicylic acid-dependent resistance. Some wild plants exhibit resistance to PstDC3000, but the mechanisms by which they achieve this resistance remain unknown. Here, we used genome-wide association mapping to identify an ATP-dependent binding cassette transporter gene (ATP-dependent binding cassette transporter G family member16) in Arabidopsis (Arabidopsis thaliana) that contributes to wild plant resistance to PstDC3000. Through microarray analysis and β-glucuronidase reporter lines, we showed that the gene is up-regulated by ABA, bacterial infection, and coronatine. We also used a green fluorescent protein fusion protein and found that transporter is more likely to localize on plasma membranes than in cell walls. Transferred DNA insertion lines exhibited consistent defective tolerance of exogenous ABA and reduced resistance to infection by PstDC3000. Our conclusion is that ATP-dependent binding cassette transporter G family member16 is involved in ABA tolerance and contributes to plant resistance against PstDC3000. This is one of the first examples, to our knowledge, of ATP-dependent binding cassette transporter involvement in plant resistance to infection by a bacterial pathogen. It also suggests a possible mechanism by which plants reduce the deleterious effects of ABA hijacking during pathogen attack. Collectively, these results improve our understanding of basal resistance in Arabidopsis and offer unique ABA-related targets for improving the innate resistance of plants to bacterial infection.
Highlights
Bacterial pathogens of plants disperse through the global hydrological cycle (Morris et al, 2008) and are likely to exert selection favoring defenses of wild plants at large spatial scales
To identify candidate genes that contribute to differences in defense against bacterial infection in wild plants, we assessed a genome-wide association (GWA) map (Fig. 1A) constructed from 96 genotypes of the RegMap panel of Arabidopsis (Supplemental Table S1) consisting of a worldwide collection of plants for which over 200,000 single nucleotide polymorphisms (SNPs) have been identified (Atwell et al, 2010)
We found no evidence of off-target effects of the transferred DNA (T-DNA) insertions (Supplemental Fig. S3), which was indicated by consistent expression of AtABCG17 and AtABCG18 in abcg16-1 and abcg16-2 relative to the Columbia-0 of Arabidopsis (Col-0) background line (CS60000)
Summary
Bacterial pathogens of plants disperse through the global hydrological cycle (Morris et al, 2008) and are likely to exert selection favoring defenses of wild plants at large spatial scales. In agriculture, these pathogens cause significant losses and necessitate extensive spraying of pesticides (Oerke, 2006). 2006), and requires the presence of a single major hormone, salicylic acid (SA; Vlot et al, 2009) This pathway is cross regulated by other signaling pathways in the plant, including those controlled by jasmonic acid (Vlot et al, 2009) and abscisic acid (ABA; de Torres-Zabala et al, 2007). We present evidence that one of the AtABCG transporters, AtABCG16, identified by genome-wide association (GWA) mapping is involved in ABA responses and plant resistance against PstDC3000
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