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 4 kb 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°C, and the highest expression was observed in M9 galactose minimal medium at 25°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 σ 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 σ70 promoter sequence (TTGCCC‐N16‐GATAAT) was observed upstream of dspB. The functionality of this second promoter was confirmed by complementation analysis. This promoter allowed constitutive expression of dspB, as measured by the expression of a dspB::uidA fusion in rich medium. In M9 galactose medium, however, HrpL was shown to activate dspB, as expression of the dspB::uidA fusion was twofold higher in a HrpL+ background than in a HrpL− background. Transposon insertions in either dspA or dspB led to a non‐pathogenic phenotype. Thus, both DspA and DspB were required for E. amylovora pathogenicity, as dspB could be expressed independently of dspA. DspA and DspB were visualized as polypeptides with apparent sizes of 190 kDa and 15.5 kDa, respectively, when encoded in the T7 polymerase/promoter system. DspA, which showed homology with the protein predicted from the partial sequence of Pseudomonas syringae pv. tomato avrE transcriptional unit III, was shown to be secreted into the external medium via the Hrp secretion pathway. DspB was predicted to be acidic, like the Syc chaperone of Yersinia. A chaperone role for DspB was suggested further by the fact that DspA secretion required a functional DspB protein.
Molecular Microbiology – Wiley
Published: Dec 1, 1997
It’s your single place to instantly
discover and read the research
that matters to you.
Enjoy affordable access to
over 18 million articles from more than
15,000 peer-reviewed journals.
All for just $49/month
Query the DeepDyve database, plus search all of PubMed and Google Scholar seamlessly
Save any article or search result from DeepDyve, PubMed, and Google Scholar... all in one place.
Get unlimited, online access to over 18 million full-text articles from more than 15,000 scientific journals.
Read from thousands of the leading scholarly journals from SpringerNature, Elsevier, Wiley-Blackwell, Oxford University Press and more.
All the latest content is available, no embargo periods.
“Hi guys, I cannot tell you how much I love this resource. Incredible. I really believe you've hit the nail on the head with this site in regards to solving the research-purchase issue.”Daniel C.
“Whoa! It’s like Spotify but for academic articles.”@Phil_Robichaud
“I must say, @deepdyve is a fabulous solution to the independent researcher's problem of #access to #information.”@deepthiw
“My last article couldn't be possible without the platform @deepdyve that makes journal papers cheaper.”@JoseServera