Nitrogen is an essential macronutrient for all living organisms and is critical for crop productivity and quality.In higher plants,inorganic nitrogen is absorbed through roots and then assimilated into amino acids by ...Nitrogen is an essential macronutrient for all living organisms and is critical for crop productivity and quality.In higher plants,inorganic nitrogen is absorbed through roots and then assimilated into amino acids by the highly conserved glutamine synthetase/glutamine:2-oxoglutarate aminotransferase(GS/GOGAT)cycle.How nitrogen metabolism and nitrogen starvation responses of plants are regulated remains largely unknown.Previous studies revealed that mutations in the rice ABNORMAL CYTOKININ RESPONSE1(ABC1)gene encoding Fd-GOGAT cause a typical nitrogen deficiency syndrome.Here,we show that ARE2(for ABC1 REPRESSOR2)is a key regulator of nitrogen starvation responses in rice.The are2 mutations partially rescue the nitrogen-deficient phenotype of abc1 and the are2 mutants show enhanced tolerance to nitrogen deficiency,suggesting that ARE2 genetically interacts with ABC1/Fd-GOGAT.ARE2 encodes a chloroplast-localized Rel A/Spo T homolog protein that catalyzes the hydrolysis of guanosine pentaphosphate or tetraphosphate(p)pp Gpp,an alarmone regulating the stringent response in bacteria under nutritional stress conditions.The are2 mutants accumulate excessive amounts of(p)pp Gpp,which correlate with lower levels of photosynthetic proteins and higher amino acid levels.Collectively,these observations suggest that the alarmone(p)pp Gpp mediates nitrogen stress responses and may constitute a highly conserved mechanism from bacteria to plants.展开更多
Antibiotics combat bacteria through their bacteriostatic(by growth inhibition)or bactericidal(by killing bacteria)action.Mechanistically,it has been proposed that bactericidal antibiotics trigger cellular damage,while...Antibiotics combat bacteria through their bacteriostatic(by growth inhibition)or bactericidal(by killing bacteria)action.Mechanistically,it has been proposed that bactericidal antibiotics trigger cellular damage,while bacteriostatic antibiotics suppress cellular metabolism.Here,we demonstrate how the difference between bacteriostatic and bactericidal activities of the antibiotic chloramphenicol can be attributed to an antibiotic-induced bacterial protective response:the stringent response.Chloramphenicol targets the ribosome to inhibit the growth of the Gram-positive bacterium Bacillus subtilis.Intriguingly,we found that chloramphenicol becomes bactericidal in B.subtilis mutants unable to produce(p)ppGpp.We observed a similar(p)ppGpp-dependent bactericidal effect of chloramphenicol in the Gram-positive pathogen Enterococcus faecalis.In B.subtilis,chloramphenicol treatment induces(p)ppGpp accumulation through the action of the(p)ppGpp synthetase RelA.(p)ppGpp subsequently depletes the intracellular concentration of GTP and antagonizes GTP action.This GTP regulation is critical for preventing chloramphenicol from killing B.subtilis,as bypassing(p)ppGpp-dependent GTP regulation potentiates chloramphenicol killing,while reducing GTP synthesis increases survival.Finally,chloramphenicol treatment protects cells from the classical bactericidal antibiotic vancomycin,reminiscent of the clinical phenomenon of antibiotic antagonism.Taken together,our findings suggest a role of(p)ppGpp in the control of the bacteriostatic and bactericidal activity of antibiotics in Gram-positive bacteria,which can be exploited to potentiate the efficacy of existing antibiotics.展开更多
基金supported by grants from the Ministry of Agriculture and Rural Affairs of China(2016ZX08009003-0022016ZX08009003-005 and 2016ZX08009003-004)+2 种基金Chinese Academy of Sciences(XDA08010401-2)the Ministry of Science and Technology of the People’s Republic of China(2016YFD0100706)the State Key Laboratory of Plant Genomics。
文摘Nitrogen is an essential macronutrient for all living organisms and is critical for crop productivity and quality.In higher plants,inorganic nitrogen is absorbed through roots and then assimilated into amino acids by the highly conserved glutamine synthetase/glutamine:2-oxoglutarate aminotransferase(GS/GOGAT)cycle.How nitrogen metabolism and nitrogen starvation responses of plants are regulated remains largely unknown.Previous studies revealed that mutations in the rice ABNORMAL CYTOKININ RESPONSE1(ABC1)gene encoding Fd-GOGAT cause a typical nitrogen deficiency syndrome.Here,we show that ARE2(for ABC1 REPRESSOR2)is a key regulator of nitrogen starvation responses in rice.The are2 mutations partially rescue the nitrogen-deficient phenotype of abc1 and the are2 mutants show enhanced tolerance to nitrogen deficiency,suggesting that ARE2 genetically interacts with ABC1/Fd-GOGAT.ARE2 encodes a chloroplast-localized Rel A/Spo T homolog protein that catalyzes the hydrolysis of guanosine pentaphosphate or tetraphosphate(p)pp Gpp,an alarmone regulating the stringent response in bacteria under nutritional stress conditions.The are2 mutants accumulate excessive amounts of(p)pp Gpp,which correlate with lower levels of photosynthetic proteins and higher amino acid levels.Collectively,these observations suggest that the alarmone(p)pp Gpp mediates nitrogen stress responses and may constitute a highly conserved mechanism from bacteria to plants.
基金supported,in part,by an R35 GM127088 Grant from NIGMS and a USDA Hatch Formula Grant from Wisconsin Agricultural Experiment Station WIS01740(to Jue D.Wang).
文摘Antibiotics combat bacteria through their bacteriostatic(by growth inhibition)or bactericidal(by killing bacteria)action.Mechanistically,it has been proposed that bactericidal antibiotics trigger cellular damage,while bacteriostatic antibiotics suppress cellular metabolism.Here,we demonstrate how the difference between bacteriostatic and bactericidal activities of the antibiotic chloramphenicol can be attributed to an antibiotic-induced bacterial protective response:the stringent response.Chloramphenicol targets the ribosome to inhibit the growth of the Gram-positive bacterium Bacillus subtilis.Intriguingly,we found that chloramphenicol becomes bactericidal in B.subtilis mutants unable to produce(p)ppGpp.We observed a similar(p)ppGpp-dependent bactericidal effect of chloramphenicol in the Gram-positive pathogen Enterococcus faecalis.In B.subtilis,chloramphenicol treatment induces(p)ppGpp accumulation through the action of the(p)ppGpp synthetase RelA.(p)ppGpp subsequently depletes the intracellular concentration of GTP and antagonizes GTP action.This GTP regulation is critical for preventing chloramphenicol from killing B.subtilis,as bypassing(p)ppGpp-dependent GTP regulation potentiates chloramphenicol killing,while reducing GTP synthesis increases survival.Finally,chloramphenicol treatment protects cells from the classical bactericidal antibiotic vancomycin,reminiscent of the clinical phenomenon of antibiotic antagonism.Taken together,our findings suggest a role of(p)ppGpp in the control of the bacteriostatic and bactericidal activity of antibiotics in Gram-positive bacteria,which can be exploited to potentiate the efficacy of existing antibiotics.
