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

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 degrees C in Escherichia coli, in a manner different from that in plant. We show that BNTR1 activates E. coli heat-shock response at low concentration in soluble form instead of in inclusion body, but BNTR1 is not functioning as a heatshock protein (HSP) because deficient temperature-sensitive mutants of HSP genes display unconspicuous thermal tolerance in the presence of BNTR1. Our further studies show that BNTR1 triggers heat-shock response by competing with s32 (s32, heat-shock transcription factor) to its binding proteins DnaJ (HSP40) and DnaK (HSP70), which results in the release and accumulation of s32, thereby promoting the heat-shock response, even under the non-heat-shock conditions. At 37 degrees C, accumulation of the HSPs induced by BNTR1 could make cells much more tolerant than those without BNTR1 at 42 degrees C. Thus, our results suggest that BNTR1 may potentially be a promising target in fermentation industry for reducing impact from temperature fluctuation, where E. coli works as bioreactors.