| Description: | Recently we identified an Arabidopsis gene, TTR1, that confers tolerance to tobacco ringspot virus (TRSV) (manuscript in preparation). Both sensitive (Estland) and tolerant (Columbia) plants can be infected with TRSV and accumulate virus antigen to similar levels. While TRSV-infected Columbia plants show few symptoms and produce seed, Estland plants elicit a systemic hypersensitive response (HR) to TRSV and die within two weeks of inoculation. The predicted sequence of the amino-terminal domain of TTR1 is most similar to the product of the tobacco N gene, a TIR-NBS-LRR resistance gene. As with N, the TTR1-induced HR is temperature sensitive. At 23C, the HR in TRSV-infected Estland plants follows the movement of TRSV through the plant. At 30C, Estland plants show no symptoms, but rapidly and uniformly develop a systemic HR when shifted to 23C. Unlike N, TTR1 contains a carboxy-terminal extension that is similar to nuclear-localized WRKY plant transcription factors. The predicted TTR1 promoter contains two W-boxes and a GCC-box.The purpose of these studies is to identify very early gene expression events in plant disease responses using the unique system we have developed for the coordinate induction of a HR. Most WRKY genes have been identified by differential gene expression analysis following wounding or exposure to pathogen elicitors. The proteins that sense these stimuli and induce the initial wave of gene expression are largely unknown. Because of its combination of pathogen recognition and transcription activation domains, we hypothesize that TTR1 is one of the elicitor-sensing proteins that initiates and/or controls disease responses.For these studies, TRSV-sensitive 'knockout' and tolerant wild-type Columbia plants will be grown and inoculated with TRSV at 30C. The Columbia TTR1 knockout contains an insertion of an Estland TTR1 gene within the Columbia TTR1 coding region and shows a systemic HR to TRSV similar to Estland. Plants will be maintained at 30C for a week to allow TRSV to move systemically and then shifted to 23C to coordinately induce the systemic HR in the sensitive Columbia line. For this initial test, mRNA will be purified from leaf tissue of the two groups of plants 1 hr after the shift to 23C. If these studies are successful, we will sample additional time points closer to the temperature shift to identify genes that are activated immediately following pathogen recognition. |
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