Abstract
Xanthomonas spp. reduce crop yields and quality worldwide. During infection of their plant hosts, many strains secrete transcription activator-like (TAL) effectors, which enter the host cell nucleus and activate specific corresponding host genes at effector binding elements (EBEs) in the promoter. TAL effectors may contribute to disease by activating the expression of susceptibility genes or trigger resistance associated with the hypersensitive reaction (HR) by activating an executor resistance (R) gene. The rice bacterial leaf streak pathogen X. oryzae pv. oryzicola (Xoc) is known to suppress host resistance, and no host R gene has been identified against it, despite considerable effort. To further investigate Xoc suppression of host resistance, we conducted a screen of effectors from BLS256 and identified Tal2a as an HR elicitor in rice when delivered heterologously by a strain of the closely related rice bacterial blight pathogen X. oryzae pv. oryzae (Xoo) or by the soybean pathogen X. axonopodis pv. glycines. The HR required the Tal2a activation domain, suggesting an executor R gene. Tal2a activity was differentially distributed among geographically diverse Xoc isolates, being largely conserved among Asian isolates. We identified four genes induced by Tal2a in next-generation RNA sequencing experiments and confirmed them using quantitative real-time reverse transcription-polymerase chain reaction (qPCR). However, neither individual nor collective activation of these genes by designer TAL effectors resulted in HR. A tal2a knockout mutant of BLS256 showed virulence comparable with the wild-type, but plasmid-based overexpression of tal2a at different levels in the wild-type reduced virulence in a directly corresponding way. Overall, the results reveal that host resistance suppression by Xoc plays a critical role in pathogenesis. Further, the dose-dependent avirulence activity of Tal2a and the apparent lack of a single canonical target that accounts for HR point to a novel, activation domain-dependent mode of action, which might involve, for example, a non-coding gene or a specific pattern of activation across multiple targets.
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Claims 8
Claim · model-written summary
Tal2a elicited rice hypersensitive response when delivered by two heterologous bacterial strains.
- Taxon
- rice
Oryza sativae0 - Interactor
- X. oryzae pv. oryzae
Xanthomonas oryzae pv. oryzaee0pathogen - Gene
- Tal2ae0
- Outcome
- HRe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“identified Tal2a as an HR elicitor in rice when delivered heterologously by a strain of the closely related rice bacterial blight pathogen X. oryzae pv. oryzae (Xoo) or by the soybean pathogen X. axonopodis pv. glycines.”
Claim · model-written summary
Tal2a triggered rice hypersensitive response when delivered by X. axonopodis pv. glycines.
- Taxon
- riceOryza sativae0
- Interactor
- X. axonopodis pv. glycinesXanthomonas citri pv. glycinese0pathogen
- Gene
- Tal2ae0
- Outcome
- HRe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“identified Tal2a as an HR elicitor in rice when delivered heterologously by a strain of the closely related rice bacterial blight pathogen X. oryzae pv. oryzae (Xoo) or by the soybean pathogen X. axonopodis pv. glycines.”
Claim · model-written summary
The Tal2a activation domain was required for hypersensitive response.
Not reportedTaxon
Verbatim
e0“The HR required the Tal2a activation domain”
Claim · model-written summary
Tal2a activity differed among Xoc isolates and was largely conserved in Asian isolates.
Not reportedTaxon
Verbatim
e0“Tal2a activity was differentially distributed among geographically diverse Xoc isolates, being largely conserved among Asian isolates.”
Claim · model-written summary
Four genes were induced by Tal2a and confirmed by qPCR.
Not reportedTaxon
Verbatim
e0“We identified four genes induced by Tal2a in next-generation RNA sequencing experiments and confirmed them using quantitative real-time reverse transcription-polymerase chain reaction (qPCR).”
Claim · model-written summary
Designer TAL effector activation of the four genes did not cause HR.
Not reportedTaxonComparator
Verbatim
e0“neither individual nor collective activation of these genes by designer TAL effectors resulted in HR.”
Claim · model-written summary
The tal2a knockout had comparable virulence to wild type.
- Material
- tal2a knockout mutant of BLS256e0
- Outcome
- virulencee0
- Direction
- comparablee0
- Comparator
- wild-typee0
Not reportedTaxon
Verbatim
e0“A tal2a knockout mutant of BLS256 showed virulence comparable with the wild-type”
Claim · model-written summary
Increasing tal2a overexpression reduced virulence correspondingly.
Not reportedTaxon
Verbatim
e0“plasmid-based overexpression of tal2a at different levels in the wild-type reduced virulence in a directly corresponding way.”
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pathogen product · disease · Oryza sativa (rice)Positive and negative results
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