An E3 ubiquitin ligase from Brassica napus induces a typical heat-shock response in its own way in Escherichia coil

Previously, we have identified a novel E3 ubiquitin ligase, BNTR1, which plays a key role in heat stress response in Brassica napus. In this study, we accidentally found that BNTR1 can also improve thermal tolerance and reduce growth inhibition at 42℃ in Escherichia coli, in a manner different from that in plant. We show that BNTR1 activates E. coil heat-shock response at low concentration in soluble form instead of in inclusion body, but BNTR1 is not functioning as a heat- shock protein （HSP） because deficient temperature-sensitive mutants of HSP genes display un- conspicuous thermal tolerance in the presence of BNTRI. Our further studies show that BNTR1 triggers heat-shock response by competing with σ32 （σ32, heat-shock transcription factor） to its binding proteins DnaJ （HSP40） and DnaK （HSP70）, which results in the release and accumulation of σ32, thereby promoting the heat-shock response, even under the non-heat-shock conditions. At 37℃, accumulation of the HSPs induced by BNTR1 could make cells much more tolerant than those without BNTR1 at 42℃. Thus, our results suggest that BNTR1 may potentially be a promis- ing target in fermentation industry for reducing impact from temperature fluctuation, where E. coli works as bioreactors.