DspA, an essential pathogenicity factor of Erwinia amylovora showing homology with AvrE of Pseudomonas syringae, is secreted via the Hrp secretion pathway in a DspB-dependent way
Abstract
In Erwinia amylovora, the dsp region, required for pathogenicity on the host plant but not for hypersensitive elicitation on tobacco, is separated from the hrp region by 4 kb. The genetic analysis reported in this paper showed that this 4kb region is not required for pathogenicity on pear seedlings. The environmental conditions allowing expression of a dsp::lacZ fusion were examined: expression was barely detected in rich medium at 30 degrees C, and the highest expression was observed in M9 galactose minimal medium at 25 degrees C. A dsp::uidA fusion appeared to be expressed only in a HrpL-proficient strain, indicating that the dsp region, like the hrp region, is positively controlled via the alternative a factor HrpL. Sequence analysis revealed that the dsp cluster encodes two genes, dspA (5517 bp) and dspB (420 bp), and that the insertions leading to the dsp::lacZ and the dsp::uidA fusions were within dspA. A HrpL-dependent promoter sequence (GGAACC-N15-CAACA) was identified upstream of dspA, and primer extension analysis detected four transcriptional starts 7, 8, 9 and 10 bp downstream of this sequence. A sigma70 promoter sequence (TTGCCC-N16-GATAAT) was observed upstream of dspB. The functionality of this second promoter wa...Continue Reading
Citations
Visualization of harpin secretion in planta during infection of apple seedlings by Erwinia amylovora
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