Despite many years of intense work investigating the function of nucleoid‐associated proteins in prokaryotes, their role in bacterial physiology remains largely unknown. The two‐dimensional protein patterns were compared and expression profiling was carried out on H‐NS‐deficient and wild‐type strains of Escherichia coli K‐12. The expression of approximately 5% of the genes and/or the accumulation of their protein was directly or indirectly altered in the hns mutant strain. About one‐fifth of these genes encode proteins that are involved in transcription or translation and one‐third are known to or were in silico predicted to encode cell envelope components or proteins that are usually involved in bacterial adaptation to changes in environmental conditions. The increased expression of several genes in the mutant resulted in a better ability of this strain to survive at low pH and high osmolarity than the wild‐type strain. In particular, the putative regulator, YhiX, plays a central role in the H‐NS control of genes required in the glutamate‐dependent acid stress response. These results suggest that there is a strong relationship between the H‐NS regulon and the maintenance of intracellular homeostasis.

Strigolactone plant hormones control plant architecture and are key players in both symbiotic and parasitic interactions. They contain an ABC tricyclic lactone connected to a butenolide group, the D-ring. The DWARF14 (D14) strigolactone receptor belongs to the superfamily of α/β-hydrolases and is known to hydrolyze the bond between the ABC lactone and the D-ring. Here we characterize the binding and catalytic functions of RAMOSUS3 (RMS3), the pea (Pisum sativum) ortholog of rice (Oryza sativa) D14 strigolactone receptor. Using novel profluorescent probes with strigolactone-like bioactivity, we show that RMS3 acts as a single-turnover enzyme that explains its apparent low enzymatic rate. We further demonstrate the formation of a covalent RMS3/D-ring complex, essential for bioactivity, in which the D-ring is attached to Histidine 247 of the catalytic triad. These results reveal an undescribed mechanism of plant hormone reception where the receptor performs an irreversible enzymatic reaction to generate its own ligand.