The Cpx envelope stress response mediates adaptation to stresses that affect protein folding within the envelope of Gram-negative bacteria. Recent transcriptome analyses revealed that the Cpx response impacts genes that affect multiple cellular functions predominantly associated with the cytoplasmic membrane. In this study, we examined the connection between the Cpx response and the respiratory complexes NADH dehydrogenase I and cytochrome bo 3 in enteropathogenic Escherichia coli. We found that the Cpx response directly represses the transcription of the nuo and cyo operons and that Cpx-mediated repression of these complexes confers adaptation to stresses that compromise envelope integrity. Furthermore, we found that the activity of the aerobic electron transport chain is reduced in E. coli lacking a functional Cpx response despite no change in the transcription of either the nuo or the cyo operon. Finally, we show that expression of NADH dehydrogenase I and cytochrome bo 3 contributes to basal Cpx pathway activity and that overproduction of individual subunits can influence pathway activation. Our results demonstrate that the Cpx response gauges and adjusts the expression, and possibly the function, of inner membrane protein complexes to enable adaptation to envelope stress.IMPORTANCE Bacterial stress responses allow microbes to survive environmental transitions and conditions, such as those encountered during infection and colonization, that would otherwise kill them. Enteric microbes that inhabit or infect the gut are exposed to a plethora of stresses, including changes in pH, nutrient composition, and the presence of other bacteria and toxic compounds. Bacteria detect and adapt to many of these conditions by using envelope stress responses that measure the presence of stressors in the outermost compartment of the bacterium by monitoring its physiology. The Cpx envelope stress response plays a role in antibiotic resistance and host colonization, and we have shown that it regulates many functions at the bacterial inner membrane. In this report, we describe a novel role for the Cpx response in sensing and controlling the expression of large, multiprotein respiratory complexes at the cytoplasmic membrane of Escherichia coli. The significance of our research is that it will increase our understanding of how these stress responses are involved in antibiotic resistance and the mechanisms used by bacteria to colonize the gut.KEYWORDS envelope stress response, NADH dehydrogenase I, cytochrome bo 3 , membrane protein biogenesis, Cpx envelope stress response, NADH dehydrogenase, cytochrome oxidase, inner membrane, protein complex, protein folding, protein localization, respiration, two-component regulatory systems G ram-negative bacteria are characterized by the structure of their cell envelope, which consists of the inner membrane (IM), the outer membrane, and the peptidoglycan layer within the periplasmic space. Of these, the IM contains the greatest protein diversity (1). Proteins that reside within the IM...

CpxP is a novel bacterial periplasmic protein with no homologues of known function. In Gram-negative enteric bacteria, CpxP is thought to interact with the two-component sensor kinase, CpxA, to inhibit induction of the Cpx envelope stress response in the absence of protein misfolding. CpxP has also been shown to facilitate DegP-mediated proteolysis of misfolded proteins. Six mutations that negate the ability of CpxP to function as a signaling protein are localized in or near two conserved LTXXQ motifs that define a class of proteins with similarity to CpxP, Pfam PF07813. To gain insight into how these mutations might affect CpxP signaling and/or proteolytic adaptor functions, the crystal structure of CpxP from Escherichia coli was determined to 2.85-Å resolution. The structure revealed an antiparallel dimer of intertwined ␣-helices with a highly basic concave surface. Each protomer consists of a long, hooked and bent hairpin fold, with the conserved LTXXQ motifs forming two diverging turns at one end. Biochemical studies demonstrated that CpxP maintains a dimeric state but may undergo a slight structural adjustment in response to the inducing cue, alkaline pH. Three of the six previously characterized cpxP loss-of-function mutations, M59T, Q55P, and Q128H, likely result from a destabilization of the protein fold, whereas the R60Q, D61E, and D61V mutations may alter intermolecular interactions.

Over the past half century, the use of nitrogen (N) fertilizers has markedly increased crop yields, but with considerable negative effects on the environment and human health. Consequently, there has been a strong push to reduce the amount of N fertilizer used by maximizing the nitrogen use efficiency (NUE) of crops. One approach would be to use classical genetics to improve the NUE of a crop plant. This involves both conventional breeding and quantitative trait loci (QTL) mapping in combination with marker-assisted selection (MAS) to track key regions of the chromosome that segregate for NUE. To achieve this goal, one of initial steps is to characterize the NUE-associated genes, then use the profiles of specific genes to combine plant physiology and genetics to improve plant performance. In this study, on the basis of genetic homology and expression analysis, barley candidate genes from a variety of families that exhibited potential roles in enhancing NUE were identified and mapped. We then performed an analysis of QTLs associated with NUE in field trials and further analyzed their map-location data to narrow the search for these candidate genes. These results provide a novel insight on the identification of NUE genes and for the future prospects, will lead to a more thorough understanding of physiological significances of the diverse gene families that may be associated with NUE in barley.

Enterohemorrhagic Escherichia coli (EHEC) is a significant human pathogen that colonizes humans and its reservoir host, cattle. Colonization requires the expression of a type 3 secretion (T3S) system that injects a mixture of effector proteins into host cells to promote bacterial attachment and disease progression. The T3S system is tightly regulated by a complex network of transcriptional and post-transcriptional regulators. Using transposon mutagenesis, here we identified the ybeZYX-Int operon as being required for normal T3S levels. Deletion analyses localized the regulation to the endoribonuclease YbeY, previously linked to 16S rRNA maturation and small RNA (sRNA) function. Loss of ybeY in EHEC had pleiotropic effects on EHEC cells, including reduced motility and growth and cold sensitivity. Using UV cross-linking and RNA-Seq (CRAC) analysis, we identified YbeY-binding sites throughout the transcriptome and discovered specific binding of YbeY to the “neck” and “beak” regions of 16S rRNA but identified no significant association of YbeY with sRNA, suggesting that YbeY modulates T3S by depleting mature ribosomes. In E. coli, translation is strongly linked to mRNA stabilization, and subinhibitory concentrations of the translation-initiation inhibitor kasugamycin provoked rapid degradation of a polycistronic mRNA encoding needle filament and needle tip proteins of the T3S system. We conclude that T3S is particularly sensitive to depletion of initiating ribosomes, explaining the inhibition of T3S in the ΔybeY strain. Accessory virulence transcripts may be preferentially degraded in cells with reduced translational capacity, potentially reflecting prioritization in protein production.

Treatment of methicillin-resistant Staphylococcus aureus infections is dependent on the efficacy of last-line antibiotics including vancomycin. Treatment failure is commonly linked to isolates with intermediate vancomycin resistance (termed VISA). These isolates have accumulated point mutations that collectively reduce vancomycin sensitivity, often by thickening the cell wall. Changes in regulatory small RNA expression have been correlated with antibiotic stress in VISA isolates however the functions of most RNA regulators is unknown. Here we capture RNA–RNA interactions associated with RNase III using CLASH. RNase III-CLASH uncovers hundreds of novel RNA–RNA interactions in vivo allowing functional characterisation of many sRNAs for the first time. Surprisingly, many mRNA–mRNA interactions are recovered and we find that an mRNA encoding a long 3′ untranslated region (UTR) (termed vigR 3′UTR) functions as a regulatory ‘hub’ within the RNA–RNA interaction network. We demonstrate that the vigR 3′UTR promotes expression of folD and the cell wall lytic transglycosylase isaA through direct mRNA–mRNA base-pairing. Deletion of the vigR 3′UTR re-sensitised VISA to glycopeptide treatment and both isaA and vigR 3′UTR deletions impact cell wall thickness. Our results demonstrate the utility of RNase III-CLASH and indicate that S. aureus uses mRNA-mRNA interactions to co-ordinate gene expression more widely than previously appreciated.