Arabidopsis thaliana EARLY FLOWERING 3 (ELF3) as a zeitnehmer (time taker) is responsible for generation of circadian rhythm and regulation of photoperiodic flowering. There are two orthologs (OsELF3-1 and OsELF3-2) of ELF3 in rice (Oryza sativa), but their roles have not yet been fully identified. Here, we performed a functional characterization of OsELF3-1 and revealed it plays a more predominant role than OsELF3-2 in rice heading. Our results suggest OsELF3-1 can affect rice circadian systems via positive regulation of OsLHY expression and negative regulation of OsPRR1, OsPRR37, OsPRR73 and OsPRR95 expression. In addition, OsELF3-1 is involved in blue light signaling by activating EARLY HEADING DATE 1 (Ehd1) expression to promote rice flowering under short-day (SD) conditions. Moreover, OsELF3-1 suppresses a flowering repressor GRAIN NUMBER, PLANT HEIGHT AND HEADING DATE 7 (Ghd7) to indirectly accelerate flowering under long-day (LD) conditions. Taken together, our results indicate OsELF3-1 is essential for circadian regulation and photoperiodic flowering in rice.

We analyzed the in vivo dynamics of peritoneal exudate cells (PECs) in mice injected with group A streptococcus (GAS). A live low-virulence strain, as well as heat-killed low- and high-virulence strains, significantly increased the number of PECs (primarily neutrophils), whereas a live high-virulence strain did not. When coinjected with thioglycollate, the live high-virulence strain, as well as most other GAS strains, suppressed the ability of thioglycollate to induce neutrophil exudation. This suppression was due to a cytocidal effect of GAS on exuded neutrophils rather than an inhibition of neutrophil migration. In addition, GAS enhanced the apoptosis of neutrophils. These cytocidal effects were significantly reduced by the deletion of functional streptolysin S from GAS. Our findings suggest that, in addition to the production of antiphagocytic factors and survival inside phagocytes, GAS uses a more aggressive method--the elimination of neutrophils--to evade the host's innate immune system.

We tested the effects of various putative efflux pump inhibitors on colistin resistance in multidrug-resistant Gram-negative bacteria. Addition of 10 mg/liter cyanide 3-chlorophenylhydrazone (CCCP) to the test medium could significantly decrease the MICs of colistin-resistant strains. Time-kill assays showed CCCP could reverse colistin resistance and inhibit the regrowth of the resistant subpopulation, especially in Acinetobacter baumannii and Stenotrophomonas maltophilia. These results suggest colistin resistance in Gram-negative bacteria can be suppressed and reversed by CCCP. Colistin is regarded as the last resort antibiotic for infections caused by multidrug-resistant (MDR) and extensively drugresistant (XDR) Gram-negative bacteria. However due to colistin's widespread use, resistant strains are increasingly being isolated in the clinic (1). Resistance to colistin has been reported to be only chromosomally mediated. However, very recently, the finding of a transferable plasmid-mediated colistin resistance gene, mcr-1, suggests the possibility of quick acquisition of resistance (2, 3). If the mcr-1 gene is similar to the case of NDM-1, colistin-resistant bacteria may soon become endemic in the world.Therefore, it is of paramount importance to prevent the dissemination of colistin resistance in an era that lacks new antibiotics against resistant Gram-negative pathogens. Besides, the finding and development of agents that effectively reverse resistance may be a promising strategy. Efflux pump inhibitors (EPIs) are potential agents in this category, and there have been initial reports on EPIs. A recent study showed that the addition of cyanide 3-chlorophenylhydrazone (CCCP) could decrease the MICs of colistin in Acinetobacter baumannii (4), but whether this phenomenon is strain specific or CCCP can reverse colistin resistance in Gram-negative bacteria deserves further investigation, and whether other commonly used EPIs have the same effects remains unknown. In order to answer these questions, we evaluated the effect of various putative EPIs on resistance to colistin in multidrug-resistant Gram-negative bacteria.Nonduplicate colistin-susceptible and colistin-resistant clinical isolates of Klebsiella pneumoniae, A. baumannii, Pseudomonas aeruginosa, and Stenotrophomonas maltophilia that also show resistance to at least other three antibiotic classes were collected between May 2014 and October 2015 from separate patients in three tertiary hospitals of Beijing, China. Colistin, CCCP, phenylarginine-␤-naphthylamide (PA␤N), 1-(1-naphthylmethyl)-piperazine (NMP), omeprazole, and verapamil standards were purchased from Sigma-Aldrich (Shanghai, China). Reserpine standards were obtained from the National Institute for the Control of Pharmaceutical and Biological Products, China (Beijing, China).MICs of EPIs, colistin, and colistin combined with EPIs were determined by the agar dilution method according to CLSI performance and interpretive guidelines (5). CCCP, NMP, and omeprazole were dissolved in dimethyl sulfoxide (DMS...

Toxoplasma gondii is a widespread intracellular pathogen infecting humans and a variety of animals. Previous studies have shown that Toxoplasma uses glucose and glutamine as the main carbon sources to support asexual reproduction, but neither nutrient is essential. Such metabolic flexibility may allow it to survive within diverse host cell types. Here, by focusing on the glycolytic enzyme pyruvate kinase (PYK) that converts phosphoenolpyruvate (PEP) into pyruvate, we found that Toxoplasma can also utilize lactate and alanine. We show that catabolism of all indicated carbon sources converges at pyruvate, and maintaining a constant pyruvate supply is critical to parasite growth. Toxoplasma expresses two PYKs: PYK1 in the cytosol and PYK2 in the apicoplast (a chloroplast relict). Genetic deletion of PYK2 did not noticeably affect parasite growth and virulence, which contrasts with the current model of carbon metabolism in the apicoplast. On the other hand, PYK1 was refractory to disruption. Conditional depletion of PYK1 resulted in global alteration of carbon metabolism, amylopectin accumulation, and reduced cellular ATP, leading to severe growth impairment. Notably, the attenuated growth of the PYK1-depleted mutant was partially rescued by lactate or alanine supplementation, and rescue by lactate required lactate dehydrogenase activity to convert it to pyruvate. Moreover, depletion of PYK1 in conjunction with PYK2 ablation led to accentuated loss of apicoplasts and complete growth arrest. Together, our results underline a critical role of pyruvate homeostasis in determining the metabolic flexibility and apicoplast maintenance, and they significantly extend our current understanding of carbon metabolism in T. gondii. IMPORTANCE Toxoplasma gondii infects almost all warm-blooded animals, and metabolic flexibility is deemed critical for its successful parasitism in diverse hosts. Glucose and glutamine are the major carbon sources to support parasite growth. In this study, we found that Toxoplasma is also competent in utilizing lactate and alanine and, thus, exhibits exceptional metabolic versatility. Notably, all these nutrients need to be converted to pyruvate to fuel the lytic cycle, and achieving a continued pyruvate supply is vital to parasite survival and metabolic flexibility. Although pyruvate can be generated by two distinct pyruvate kinases, located in cytosol and apicoplast, respectively, the cytosolic enzyme is the main source of subcellular pyruvate, and cooperative usage of pyruvate among multiple organelles is critical for parasite growth and virulence. These findings expand our current understanding of carbon metabolism in Toxoplasma gondii and related parasites while providing a basis for designing novel antiparasitic interventions.