Nutrient reabsorption mechanism adapted to low phosphorus in wild and cultivated soybean varieties

Phosphorus (P) is an essential nutrient element for plants. Wild soybean (Glycine soja) expresses higher tolerance to P-limited environment compared to cultivated soybeans (Glycine max). In this study, the response of ionomics and metabonomics in young and old leaves of two soybean varieties under low P were studied. Our results showed that the tolerance of low P in wild soybean can be improved by promoting the accumulation of Mg2+, Fe3+, and SO42- in young and old leaves and the transportation of NO3− and H2PO4− from old to young leaves. The young and old leaves of wild soybean under low P accumulated sugars including maltose and sucrose, amino acids including asparagine and glutamine, and nitrogenous compounds including tyramine, and enhanced the tricarboxylic acid cycle metabolism, especially in young leaves, but decreased the content of hexose-phosphate metabolites. Our experiment indicated that wild soybean can tolerate low P by enhancing the energy metabolism in young and old leaves, promoting the transportation and reuse of sugars and amino acid metabolites from old to young leaves, and mobilizing Pi from hexose-phosphate of old leaves to young leaves. Our results provide a new insight for the cultivation of new soybean varieties with tolerance to P deficiency.

Legionella pneumophilaIs Directly Sensitive to 2-Deoxyglucose-Phosphate via Its UhpC Transporter but Is Indifferent to Shifts in Host Cell Glycolytic Metabolism

ABSTRACTToll-like receptor (TLR) stimulation induces a pronounced shift to increased glycolytic metabolism in mammalian macrophages. We observed that bone marrow-derived macrophages (BMMs) increase glycolysis in response to infection withLegionella pneumophila, but the role of host macrophage glycolysis in terms of intracellularL. pneumophilareplication is not currently understood. Treatment with 2-deoxyglucose (2DG) blocksL. pneumophilareplication in mammalian macrophages but has no effect on bacteria grown in broth. In addition, we found that 2DG had no effect on bacteria grown in amoebae. We used a serial enrichment strategy to reveal that the effect of 2DG onL. pneumophilain macrophages requires theL. pneumophilahexose-phosphate transporter UhpC. Experiments with UhpC-deficientL. pneumophilarevealed that mutant bacteria are also resistant to growth inhibition following treatment with phosphorylated 2DG in broth, suggesting that the inhibitory effect of 2DG onL. pneumophilain mammalian cells requires 2DG phosphorylation. UhpC-deficientL. pneumophilareplicates without a growth defect in BMMs and protozoan host cells and also replicates without a growth defect in BMMs treated with 2DG. Our data indicate that neither TLR signaling-dependent increased macrophage glycolysis nor inhibition of macrophage glycolysis has a substantial effect on intracellularL. pneumophilareplication. These results are consistent with the view thatL. pneumophilacan employ diverse metabolic strategies to exploit its host cells.IMPORTANCEWe explored the relationship between macrophage glycolysis and replication of an intracellular bacterial pathogen,Legionella pneumophila. Previous studies demonstrated that a glycolysis inhibitor, 2-deoxyglucose (2DG), blocks replication ofL. pneumophiladuring infection of macrophages, leading to speculation thatL. pneumophilamay exploit macrophage glycolysis. We isolatedL. pneumophilamutants resistant to the inhibitory effect of 2DG in macrophages, identifying aL. pneumophilahexose-phosphate transporter, UhpC, that is required for bacterial sensitivity to 2DG during infection. Our results reveal how a bacterial transporter mediates the direct antimicrobial effect of a toxic metabolite. Moreover, our results indicate that neither induction nor impairment of host glycolysis inhibits intracellular replication ofL. pneumophila, which is consistent with a view ofL. pneumophilaas a metabolic generalist.

Characterization of a Novel Two-Component Regulatory System, HptRS, the Regulator for the Hexose Phosphate Transport System in Staphylococcus aureus

Hexose phosphate is an important carbon source within the cytoplasm of host cells. Bacterial pathogens that invade, survive, and multiply within various host epithelial cells exploit hexose phosphates from the host cytoplasm through thehexosephosphatetransport (HPT) system to gain energy and synthesize cellular components. InEscherichia coli, the HPT system consists of a two-component regulatory system (UhpAB) and a phosphate sensor protein (UhpC) that tightly regulate expression of a hexose phosphate transporter (UhpT). Although growing evidence suggests thatStaphylococcus aureusalso can invade, survive, and multiply within various host epithelial cells, the genetic elements involved in the HPT system inS. aureushave not been characterized yet. In this study, we identified and characterized the HPT system inS. aureusthat includes thehptRS(a novel two-component regulatory system), thehptA(a putative phosphate sensor), and theuhpT(a hexose phosphate transporter) genes. ThehptA,hptRS, anduhpTmarkerless deletion mutants were generated by an allelic replacement method using a modified pMAD-CM-GFPuv vector system. We demonstrated that bothhptAandhptRSare required to positively regulate transcription ofuhpTin response to extracellular phosphates, such as glycerol-3-phosphate (G3P), glucose-6-phosphate (G6P), and fosfomycin. Mutational studies revealed that disruption of thehptA,hptRS, oruhpTgene impaired the growth of bacteria when the available carbon source was limited to G6P, impaired survival/multiplication within various types of host cells, and increased resistance to fosfomycin. The results of this study suggest that the HPT system plays an important role in adaptation ofS. aureuswithin the host cells and could be an important target for developing novel antistaphylococcal therapies.