Core and variable antimicrobial resistance genes in the gut microbiomes of Chinese and European pigs

Monitoring the prevalence of antimicrobial resistance genes(ARGs)is vital for addressing the global crisis of antibiotic-resistant bacterial infections.Despite its importance,the characterization of ARGs and microbiome structures,as well as the identification of indicators for routine ARG monitoring in pig farms,are still lacking,particularly concerning variations in antimicrobial exposure in different countries or regions.Here,metagenomics and random forest machine learning were used to elucidate the ARG profiles,microbiome structures,and ARG contamination indicators in pig manure under different antimicrobial pressures between China and Europe.Results showed that Chinese pigs exposed to high-level antimicrobials exhibited higher total and plasmid-mediated ARG abundances compared to those in European pigs(P<0.05).ANT(6)-Ib,APH(3')-IIIa,and tet(40)were identified as shared core ARGs between the two pig populations.Furthermore,the core ARGs identified in pig populations were correlated with those found in human populations within the same geographical regions.Lactobacillus and Prevotella were identified as the dominant genera in the core microbiomes of Chinese and European pigs,respectively.Forty ARG markers and 43 biomarkers were able to differentiate between the Chinese and European pig manure samples with accuracies of 100%and 98.7%,respectively.Indicators for assessing ARG contamination in Chinese and European pigs also achieved high accuracy(r=0.72-0.88).Escherichia flexneri in both Chinese and European pig populations carried between 21 and 37 ARGs.The results of this study emphasize the importance of global collaboration in reducing antimicrobial resistance risk and provide validated indicators for evaluating the risk of ARG contamination in pig farms.

Fate and Behavior of Tetracycline Resistance Genes in Activated Carbon Adsorption

The accessibility of tetracycline resistance gene (tetG) into the pores of activated carbon (AC), as well as the impact of the pore size distribution (PSD) of AC on the uptake capacity of tetG, were investigated using eight types of AC (four coal-based and four wood-based). AC showed the capability to admit tetG and the average reduction of tetG for coal-based and wood-based ACs at the AC dose of 1 g·L-1 was 3.12 log and 3.65 log, respectively. The uptake kinetic analysis showed that the uptake of the gene followed the pseudo-second-order kinetics reaction, and the uptake rate constant for the coal-based and wood-based ACs was in the range of 5.97 × 10-12 - 4.64 × 10-9 and 7.02 × 10-11 - 1.59 × 10-8 copies·mg-1·min-1, respectively. The uptake capacity analysis by fitting the obtained experiment data with the Freundlich isotherm model indicated that the uptake constant (KF) values were 1.71 × 103 - 8.00 × 109 (copies·g-1)1-1/n for coal-based ACs and 7.00 × 108 - 3.00 × 1010 (copies·g-1)1-1/n for wood-based ones. In addition, the correlation analysis between KF values and pore volume as well as pore surface at different pore size regions of ACs showed that relatively higher positive correlation was found for pores of 50 - 100 Å, suggesting ACs with more pores in this size region can uptake more tetG. The findings of this study are valuable as reference for optimizing the adsorption process regarding antibiotic resistance-related concerns in drinking water treatment.

Mobile genetic elements facilitate the transmission of antibiotic resistance genes in multidrug-resistant Enterobacteriaceae from duck farms

Multidrug-resistant(MDR)Enterobacteriaceae critically threaten duck farming and public health.The phenotypes,genotypes,and associated mobile genetic elements(MGEs)of MDR Enterobacteriaceae isolated from 6 duck farms in Zhejiang Province,China,were investigated.A total of 215 isolates were identified as Escherichia coli(64.65%),Klebsiella pneumoniae(12.09%),Proteus mirabilis(10.23%),Salmonella(8.84%),and Enterobacter cloacae(4.19%).Meanwhile,all isolates were resistant to at least two antibiotics.Most isolates carried tet(A)(85.12%),blaTEM(78.60%)and sul1(67.44%)resistance genes.Gene co-occurrence analysis showed that the resistance genes were associated with IS26 and integrons.A conjugative IncFII plasmid pSDM004 containing all the above MGEs was detected in Proteus mirabilis isolate SDM004.This isolate was resistant to 18 antibiotics and carried the blaNDM-5 gene.MGEs,especially plasmids,are the primary antibiotic resistance gene transmission route in duck farms.These findings provide a theoretical basis for the rational use of antibiotics in farms which are substantial for evaluating public health and food safety.

Trifunctional Cu-Mesh/Cu_(2)O@FeO Nanoarrays for Highly Efficient Degradation of Antibiotic, Inactivation of Antibiotic-Resistant Bacteria, and Damage of Antibiotics Resistance Genes

Trifunctional Cu-mesh/Cu_(2)O@FeO nanoarrays heterostructure is designed and fabricated by integrating CuCu_(2)O@FeO nanoarrays onto Cu-mesh(CM)via an in situ growth and phase transformation process.It is successfully applied to efficiently mitigate the antibiotic pollution,including degradation of antibiotics,inactivation of antibiotic-resistant bacteria(ARB),and damage of antibiotics resistance genes(ARGs).Under visible-light irradiation,CM/CuCu_(2)O@FeO nanoarrays exhibit a superior degradation efficiency on antibiotics(e.g.,up to 99%in 25 min for tetracycline hydrochloride,TC),due to the generated reactive oxygen species(ROS),especially the dominant·O^(2−).It can fully inactivate E.coli(HB101)with initial number of~108 CFU mL^(−1) in 10 min,which is mainly attributed to the synergistic effects of 1D nanostructure,dissolved metal ions,and generated ROS.Meanwhile,it is able to damage ARGs after 180 min of photodegradation,including tetA(vs TC)of 3.3 log 10,aphA(vs kanamycin sulfate,KAN)of 3.4 log 10,and tnpA(vs ampicillin,AMP)of 4.4 log 10,respectively.This work explores a green way for treating antibiotic pollution under visible light.

Preliminary Study on the Treatment Efficiency of Pasteurized Lime Thermal Alkaline Hydrolysis for Excess Activated Sludge and Reduction of Tetracycline Resistance Genes

Thermal alkaline hydrolysis is a common pretreatment method for the utilization of excess activated sludge(EAS).Owing to strict environment laws and need for better energy utilization,new methods were developed in this study to improve the efficiency of pretreatment method.Direct thermal hydrolysis(TH),pasteurized thermal hydrolysis(PTH),and alkaline pasteurized thermal hydrolysis(PTH+CaO and PTH+NaOH)methods were used to treat EAS.Each method was compared and analyzed in terms of dissolution in ammonium nitrogen(NH_(4)^(+)-N)and soluble COD(SCOD)in EAS.Furthermore,the removal of tetracycline resistance genes(TRGs)and class 1 transposon gene intI1 from EAS was investigated.The NH_(4)^(+)-N and SCOD concentrations in EAS treated by PTH were 1.24 and 2.58 times higher than those of TH.However,the removal efficiency of total TRGs and intI1 between the groups was comparable.The SCOD concentration of the PTH+NaOH group was 4.37 times higher than that of the PTH group,and the removal efficiency of total TRGs was increased by 9.52%compared with that by PTH.The NH_(4)^(+)-N and SCOD concentrations of the PTH+CaO group could reach 85.04%and 92.14%of the PTH+NaOH group,but the removal efficiency of total TRGs by PTH+CaO was 19.78%lower than that by PTH+NaOH.Thus,to reduce the financial cost in actual operation,lime(CaO)can be used instead of a strong alkali(NaOH),and pasteurized steam at 70℃ instead of conventional high-temperature heating to treat EAS.This study provides a reference for the development of alkaline hydrolysis under moderate temperatures along with the removal of TRGs in EAS.

Effects of Microplastics on Expression of Resistance Genes and Virulence Genes of Vibrio alginolyticus

[Objectives]To study the effects of microplastics on antibiotic resistance genes and virulence genes of Vibrio alginolyticus,so as to provide a certain reference for controlling marine pollution,curbing the spread of environmental antibiotic resistance genes and virulence genes,formulating environmental policies,and maintaining food safety.[Methods]After adding V.alginolyticus into the artificial seawater,they were divided into three groups,namely blank control group(BLK),polyvinyl chloride microplastic group(PVC group)and polyvinyl alcohol microplastic group(PVA group).Aerated culture experiments were carried out,and the effects of microplastics on the expression of resistance genes and virulence genes of V.alginolyticus were studied by PCR and qPCR methods.[Results]The presence of microplastics significantly changed the resistance gene structure of V.alginolyticus.Compared with the control group,the cfxA and cfr resistance genes were detected in the microplastic group.However,only PVC group detected blaZ resistance gene,and only PVA group did not detect aaC resistance gene.In addition,compared with the control group,the expressions of virulence genes in the microplastic group were all down-regulated(P<0.01).[Conclusions]This study provides some reference for curbing the spread of environmental antibiotic resistance genes and virulence genes,formulating environmental policies,and maintaining food safety,but the specific mechanisms of drug resistance and virulence need further research.

Molecular Screening of Rice Cultivated in Benin for the Identification of Xanthomonas oryzae Pv. oryzae and Bacterial Leaf Blight Resistance Genes

One of the most devastating diseases of rice worldwide is bacterial blight (BLB) caused by Xanthomonas oryzae pv. Oryzae (Xoo). In Benin, Xoo was first described in 2013 on wild rice Oryzae longistaminata. So far, no study has been done on Beninese Xoo strains. We do not know whether the pathogen has already passed into the rice varieties grown, or if they are exposed to other bacteria. Whereas the use of resistant varieties, carrying resistance genes, is the only highly effective and environmentally friendly way to control this disease, no information is available on these Xoo resistance genes in rice varieties grown in Benin apart from the one we recently. This study aims to identify Beninese Xoo strains, causing BLB and screen rice varieties grown in Benin for the main resistance genes. Diseased rice leaves showing typical symptoms of fire blight collected from different rice fields in the three phytogeographic areas of Benin were analyzed by PCR for Xoo-specific sequence identification. Furthermore, seventy-five collected rice accessions were screened to identify xa5, Xa7, xa13, and Xa21 resistance genes to Xoo. The results reveal that Xanthomonas oryzae was identified in two fields in Banikouara and one in Malanville. On the other hand, Sphingomonas sp. has been identified in several other rice fields in Benin. Forty-seven of seventy-five rice accessions examined (62.66%) carried Xoo resistance genes with 3 (4%) and 40 (53.33%) of xa5 and Xa21 respectively. None of the accessions had either Xa7 or xa13 resistance genes. Three accessions possess both xa5 and Xa21 genes. Isogenic lines IRBB60 and IRBB21, supposed to be a positive control, presented a Xoo sensitivity allele. These results indicate that Xoo has moved from the wild rice variety to the cultivated variety in northern Benin and varietal improvement programs must be implemented with varieties having several resistance genes for the efficient response against a possible BLB pandemic in Benin.

Recent Progress in Elucidating the Structure, Function and Evolution of Disease Resistance Genes in Plants

Plants employ multifaceted mechanisms to fight with numerous pathogens in nature. Resistance （R） genes are the most effective weapons against pathogen invasion since they can specifically recognize the corresponding pathogen effectors or associated protein（s） to activate plant immune responses at the site of infection. Up to date, over 70 R genes have been isolated from various plant species. Most R proteins contain conserved motifs such as nucleotide-binding site （NBS）, leucine-rich repeat （LRR）, Toll-interleukin-1 receptor domain （TIR, homologous to cytoplasmic domains of the Drosophila Toll protein and the manamalian intefleukin-1 receptor）, coiled-coil （CC） or leucine zipper （LZ） structure and protein kinase domain （PK）. Recent results indicate that these domains play significant roles in R protein interactions with effector proteins from pathogens and in activating signal transduction pathways involved in innate immunity. This review highlights an overview of the recent progress in elucidating the structure, function and evolution of the isolated R genes in different plant-pathogen interaction systems.

Genotypic Analysis of Rice Blast Resistance Genes Pi-ta and Pi-b in Japonica Rice Varieties and Lines in Jiangsu Province

Pi-ta and Pi-b, the first cloned rice blast resistant genes, have been wide- ly used in rice blast resistance breeding for their lasting and stable resistance. To define the distribution of Pi-ta and Pi-b in japonica rice in Jiangsu, the genotypes of resistance genes Pi-ta and Pi-b in 40 varieties and 665 new lines were detected using functional markers of Pi-ta/pi-ta and Pi-b^pi-b alleles. The results showed that the resistance alleles of Pi-ta and Pi-b were widely spread in japonica rice varieties, and the distribution frequency of Pi-b was higher than that of Pi-ta. Most of the Lianjing serial varieties didn＇t carry the two resistance genes, but the two resistance genes were widely distributed in Wujing serial varieties. There was no significant dif- ference in distribution frequency of Pi-ta between new lines and commercial vari- eties. However, the distribution frequency of Pi-b in new lines was higher than that in commercial varieties. It was indicated that artificial selection was conducive to the improvement of distribution frequency of Pi-b in rice varieties. Among the 4 genotypes, the distribution frequency of pi-taJPi-b was highest （60.0%）, followed by Pi-ta/ Pi-b （33.5%） and pi-ta/pi-b （3.9%）. The frequency of Pi-taJpi-b was lowest, account- ing for only 2.6%. In terms of source of resistance genes in the four combinations, the resistant allele Pi-ta might be from parents of Wuxiangjing14, Wujing15 or Nanjing44, and Pi-b might come from parents of Wujing13, Wuxiangjing14, Wujing15 or Nanjing44. The analysis on the genotypic frequencies in offspring of the rice vari- eties showed that the resistance genotype of Pi-ta/Pi-b had the highest frequency in the cross combination of Nanjing44//Wujing13/Kantou194.

Molecular Detection of Resistance Genes to Stripe Rust and Powdery Mildew in Common Wheat Cultivar Yunmai52

Yunmai52, developed by crossing with common wheat-Haynaldia villosa6AL/6VS translocation line 92R149 as a resistant parent in 1992, was a common wheat cultivar approved and released in 2007 in Yunnan Province, China, which is characterized by high resistance to powdery mildew and stripe rust. In this study,an F_2 population derived from a cross K78S/Yunmai52 was constructed to investigate the resistance genes, where K78 S is a wheat male sterile line susceptible to powdery mildew and stripe rust. Phenotypic identification of the parents, F_1 and F_2 populations and chi-square analyses showed that F_1 population was immune to stripe rust and powdery mildew; the segregation ratio of resistance and susceptibility to powdery mildew（χ~2=1.10χ~2_（1,0.05）=3.84） and stripe rust（χ~2=0.15χ~2_（1,0.05）=3.84） fit to a 3：1 ratio in F_2 population, indicating that Yunmai52 harbors a dominant stripe rust resistance gene and a dominant powdery mildew resistance gene. The individuals were further detected with a marker co-segregated with Pm21（SCAR_（1400）） and two markers closely linked with Yr26（XWe173 and Xbarc181）. The results showed that polymorphic bands could be amplified between the parents and between resistance and susceptibility gene pools at the same locus. Randomly 96 individuals of F_2 population were selected for verification. The results showed that the phenotype was significantly correlated with the genotype. The detection accuracy of markers SCAR_（1400）, XWe173 and Xbarc181 was 100%, 97.91% and 92.70%, respectively.Yunmai52 harbored powdery mildew resistance gene Pm21 and stripe rust resistance gene Yr26, which were both derived from 6AL/6VS translocation line 92R149.In addition, the results also demonstrate that Pm21 and Yr26 are two genes conferring durable resistance to powdery mildew and stripe rust in wheat.

Screening of Effective Resistance Genes and Resistant Rice Parents against Rice Bacterial Blight(Xanthomonas oryzae pv. Oryzae) in Guangxi Province

[ Objective ] The paper was to confirm the resistance genes and resistant parents of rice against bacterial blight that could be used in Guangxi Province. [ Method] The dominant pathogenic types Ⅳ of Xanthomonas Oryzae pv. Oryzae in Guangxi were inoculated on a set of monogenic rice lines, the main hybrid rice parents in Guangxi and some important rice germplasm resources, and its resistant and susceptible conditions were investigated. [ Result ] IRBBS, IRBB7 and CBB23 were the resistant rice parents with resistance against pathogenic type IV, which contained resistance genes xa5, Xa7 and Xa23, respectively, and were identified to be the effective resistance genes against pathogenic type Ⅳ of X. Oryzae in Guangxi. [ Conclusion] The results provided basis for resistance breeding against bacterial blight.

Establishment and Application of a Multiplex PCR System for the Detection of Blast Resistance Genes Pi-ta and Pi-b in Rice

Rice blast is one of the important diseases in major rice producing areas of China. The main blast resistance genes Pi-ta and Pi-b showed broad-spectrum and durable resistance to rice blast in many rice growing areas of China, which have been widely utilized in rice breeding and commercial production. In this study, on the basis of detection and verification of the genotypes of 22 rice varieties har- boring known blast resistance genes （Pi-ta and Pi-b） and blast susceptibility genes （pi-ta and pi-b）, two multiple PCR systems for these genes were established by us- ing the functional markers of blast resistance genes Pi-ta and Pi-b as well as blast susceptibility genes pi-ta and pi-b, respectively. Specifically, multiple PCR system I could simultaneously detect blast resistance genes Pi-ta and Pi-b, while system II could detect simultaneously blast susceptibility genes pi-ta and pi-b. In addition, the genotypes of 336 high generation breeding materials were detected with these two multiple PCR systems. The results were highly consistent with those of conventional single mark detection, indicating that these two multiplex PCR systems were stable, reliable and time-saving. The established multiplex PCR systems may serve as a rapid and efficient method to identify and screen rice germplasm resources and can be applied in marker-assisted selection to polymerize multiple genes for blast resis- tance in rice breeding.

Postulation of Seedlings Resistance Genes to Yellow Rust in Commercial Wheat Cultivars from Yunnan Province in China

The objective of this study was to characterize yellow （stripe） rust resistance gene（s） in 52 commercial wheat cultivars from Yunnan Province in China, and to provide information for their rational deployment in field. Seedlings of wheat cultivars were inoculated with 25 differential isolates ofPuccinia striiformis from foreign and home to postulate resistance genes to yellow rust, and then validated by pedigree. There were 10 probable resistance genes characterized in these cultivars, in which, Yr9 was most commonly postulated to be present in thirteen cultivars. Yr21, the second, was present in four cultivars. Yr8, the third, were present in three cultivars. Yr6, Yrl 7 and Yr26, the fourth, was present in two cultivars respectively. The other gene（s） such as, Yr2＋YrA, Yr7 and Yr27, were only present in single cultivar（s）; unknown gene（s） or gene（s） combination（s） were present in 22 cultivars. One cultivar （Yunmai 42） had no resistance gene tested in this study. Cultivars such as Yunmai 52, Mian 1971-98, Kunmai 4, and Yunmai 56 carried effective genes and can be popularized mainly; Yr9 should be planted with other Yr genes. In the meantime other effective genes should be introduced to realize gene diversity for controlling wheat yellow rust. Yunmai 42 should be reduced to avoid rust breakout. Unknown gene cultivars should be utilized and be researched deeply.

Marker-assisted pyramiding of soybean resistance genes R_(SC4),R_(SC8),and R_(SC14Q) to soybean mosaic virus

Soybean mosaic virus （SMV） is one of the major viral pathogens affecting soybean crops worldwide. Three SMV resistance genes, Rsc4, Rsc8, and Rsc14Q, have been identified and mapped on soybean chromosomes 14, 2, and 13 from Dabaima, Kefeng 1, and Qihuang 1 cultivars, respectively. Soybean cultivar Nannong 1138-2 is widely grown in the Yangtze River Valley of China. In this study, crosses were made between Qihuang l^Kefeng 1 and DabaimaxNannong 1138-2. Ten simple sequence repeat （SSR） markers linked to three resistance loci （Rsc4, Rsc8, and Rsc^4Q） were used to assist pyramided breeding. Pyramided families containing three resistance loci （Rsc4, Rsc8, and Rsc14Q） were evaluated by inoculating them with 21 SMV strains from China. Results indicated that the 10 markers can be used effectively to assist the selection of resistant individuals containing Rsc4, Rsc8, and Rsc14Q. A total of 53 F6 plants were confirmed to contain three homozygous alleles conferring resistance to SMV. Five F7 homozygous pyramided families exhibited resistance to 21 strains of SMV and showed desirable agronomic traits using dual selection. The strategy of pyramiding resistance gene derived from different varieties has practical breeding value in providing broad-spectrum resistance against the existing strains of SMV in China.

Molecular and Physical Mapping of Powdery Mildew Resistance Genes and QTLs in Wheat: A Review

Wheat powdery mildew （Pro） is a major disease of wheat worldwide. During the past years, numerous studies have been published on molecular mapping of Pm resistance gene（s） in wheat. We summarized the relevant findings of 89 major re- sistance gene mapping studies and 25 quantitative trait loci （QTL） mapping studies. Major Pm resistance genes and QTLs were found on all wheat chromosomes, but the Pm resistance genes/QTLs were not randomly distributed on each chromosome of wheat. The summarized data showed that the A or B genome has more major Pm resistance genes than the D genome and chromosomes 1A, 2A, 2B, 5B, 5D, 6B, 7A and 7B harbor more major Pm resistance genes than the other chromosomes. For adult plant resistance （APR） genes/QTLs, B genome of wheat harbors more APR genes than A and D genomes, and chromo- somes 2A, 4A, 5A, 1B, 2B, 3B, 5B, 6B, 7B, 2D, 5D and 7D harbor more Pm resistance QTLs than the other chromosomes, suggesting that A genome except 1A, 3A and 6A, B genome except 4B, D genome except 1D, 3D, 4D, and 6D play an impor- tant role in wheat combating against powdery mildew. Furthermore, Pm resistance genes are derived from wheat and its rela- tives, which suggested that the resistance sources are diverse and Pm resistance genes are diverse and useful in combating against the powdery mildew isolates. In this review, four APR genes, Pm38/Lr34/Yr18/Sr57, Pm46/Lr67/Yr46/Sr55, Pm？/Lr27/Yr30/ SY2 and Pm39/Lr46/Yr29, are not only resistant to powdery mildew but also effective for rust diseases in the field, indicating that such genes are stable and useful in wheat breeding programmes. The summarized data also provide chromosome locations or linked markers for Pm resistance genes/QTLs. Markers linked to these genes can also be utilized to pyramid diverse Pm resis- tance genes/QTLs more efficiently by marker-assisted selection.

Seafood as a Reservoir of Gram-negative Bacteria Carrying Integrons and Antimicrobial Resistance Genes in Japan

PCR and DNA sequencing were used to screen and characterize integrons and resistance genes in Gram-negative bacteria isolated from seafood products in Japan.A total of 215 Gram-negative bacteria were isolated from local and imported seafood samples collected from retail markets in Hiroshima Prefecture.Class 1 integrons containing gene cassettes encoding resistance to trimethoprim

Screening and identification of candidate Fusarium wilt-resistance genes from pumpkin

Pumpkin(Cucurbita moschata)has been widely used as cucumber(Cucumis sativus L.)rootstock to defend against Fusarium wilt(FW)and increase cucumber yields and profits.However,the resistance genes and mechanisms underlying the FW tolerance in pumpkin are poorly understood.Here we analyzed the transcriptome of pumpkin inoculated with the cucumber FW causal agent Fusarium oxysporum f.sp.cucumerinum(Foc),and obtained 3152 and 4735 upregulated genes induced by Foc at 24h after Foc inoculation compared with at 0h and 24h non-inoculated control,respectively.Next,404 common differentially expressed genes(DEGs)were screened using the criterion log_(2) FPKM(fold change)≥2.In total,206 of 404 DEGs were predominantly expressed in roots,which is the first tissue that Foc contacts and invades.140 DEGs were selected and classified into four groups(pathogenesis resistance,secondary metabolism-related,transcription factor and signal binding)based on their functional descriptions.Then,29 genes having high expression levels were selected to investigate the expression patterns induced by a Foc inoculation.Among them,16 genes were significantly induced by Foc and showed high expression levels at various treatment time points.These candidate genes may act as positive regulators of FW resistance in pumpkin and provide effective resources for improving cucumber FW resistance through breeding programs.

Cytogenetic Mapping of Disease Resistance Genes and Analysis of Their Distribution Features on Chromosomes in Maize

Cytogenetic maps of four clusters of disease resistance genes were generated by ISH of the two RFLP markers tightly linked to and flanking each of maize resistance genes and the cloned resistance genes from other plant species onto maize chromosomes, combining with data published before. These genes include Helminthosporium turcium Pass resistance genes Ht1, Htn1 and Ht2, Helminthosporium maydis Nisik resistance genes Rhm1 and Rhm2, maize dwarf mosaic virus resistance gene Mdm1, wheat streak mosaic virus resistance gene Wsm1, Helminthosporium carbonum ULLstrup resistance gene Hml and the cloned Xanthomonas oryzae pv. Oryzae resistance gene Xa21 of rice, Cladosporium fulvum resistance genes Cf-9 and Cf-2.1 of tomato,and Pseudomonas syringae resistance gene RPS2 of Arabidopsis. Most of the tested disease resistance genes located on the four chromosomes, i.e., chromosomes1, 3, 6 and 8, and they closely distributed at the interstitial regions of these chromosomal long arms with percentage distances ranging 31.44(±3.72)-72.40(±3.25) except for genes Rhm1, Rhm2, Mdm1 and Wsm1 which mapped on the satellites of the short arms of chromosome6. It showed that the tested RFLP markers and genes were duplicated or triplicated in maize genome. Homology and conservation of disease resistance genes among species, and relationship between distribution features and functions of the genes were discussed. The results provide important scientific basis for deeply understanding structure and function of disease resistance genes and breeding in maize.

Response to Comment on "The role of wildlife (wild birds) in the global transmission of antimicrobial resistance genes"

DEAR EDITOR,Since our first identification of plasmid-mediated colistin resistance gene mcr-1 in 2015 （Liu et al., 2016）, it has been described in human clinics, domestic animals, foods, and the environment worldwide （Schwarz ＆ Johnson, 2016）. Although it is still rare, the emergence of mcr-I in wild animals is of great concern. We summarized two previous reports on mcr-1 in wild birds from Lithuania and Argentina to describe its emergence and characteristics in wildlife and highlight the potentially important role of wild animals, particularly birds, in its global transmission （Wang et al., 2017）. The first detection of mcr-1 in wildlife in Asia was identified in an extended-spectrum β- lactamase-producing Escherichia coil strain isolated from Eurasian coot （Fulica atra）,

Analysis of antibiotic resistance genes and their effects on marine environment

The application of overgrowth antibiotic resistance genes in marine research was discussed.Using the China National Knowledge Infrastructure(CNKI)network database to retrieve papers on resistance genes(n=30627)and antibiotic resistance genes(n=3277),the published trends,subject headings and other aspects of bibliometrics were analyzed.Literature in this field has increased rapidly in the past 38 years.55.3%of the papers were published in the last ten years,31.2%of the papers were published in the last five years.The relevance of research topics has increased in recent years,the current research mainly focus on antibiotics,resistance gene,antibiotic resistance gene,and drug resistance.Literature analysis is helpful to understand the overall development trend of overgrowth antibiotic resistance genes in marine research.