The Genomic Sequencing And Annotation Of The Tea-plant Endophytic Herbaspirillum Sp.WT00C Strain

Herbaspirillum WT00C strain,isolated from tea plant by our laboratory,is an endophytic bacterium.Previous studies found that it had the capability of producing indole-3-acetic acid?IAA?,ammonia and siderophore.It went to tea plants via traumatic infection,and was unable to infect plants by irrigation or sprinkling.This bacterium colonized only in tea plant,rather than in other crops such as Brassica campestris,Brassica rape,Oryza sative,Triticum aestivum and Chlorophytum comosum.Field studies showed that Herbaspirillum WT00C strain stimulated lateral root formation and bud growth of tea cutting via soaking method,and also promoted the growth of newborn shoots by inoculating the bacterium to the upper incision of tea twigs pruned with a trimmer in the field.In the field study,the biomass of newborn shoots was increased up to8 kg/acre.Similar to two nitrogen-fixing bacteria H.seropedicae and H.rubrisubalbican,Herbaspirillum sp.WT00C strain is also a plant growth-promoting bacterium.Different from two bacteria,it does not display any nitrogen-fixing activity and has a specific host tea plant.To understand its plant-growth promotion and host specificity,the whole genome of Herbaspirillum WT00C was sequenced and annotated by using those methods of molecular biology and bioinformatics in this study.The genome of Herbaspirillum sp.WT00C is composed of 6,079,821 base pairs with a total of 5,537 genes.The average length of gene is 955 bp.Genomic annotation reveals that this bacterium holds four terminal oxidases,an ABC sugar transporter and a PTS system,indicating that Herbaspirillum sp.WT00C has the capacity to metabolize a wide range of carbohydrates.Carbohydrates are metabolized through the pentose phosphate pathway and Entner-Doudoroff pathway in Herbaspirillum sp.WT00C,other than glycolysis used usually by most living organisms.Herbaspirillum sp.WT00C is able to synthesize and metabolize most amino acids except for L-leucine,L-isoleucine,L-lysine and L-histidine.Those amino acids may be synthesized via transamination of aminotransferases.Herbaspirillum sp.WT00C also has an intact metabolic pathway for both anabolism of fatty acids starting from acetyl-CoA and catabolism of fatty acids in which acetyl-CoA is the final metabolin.Interestingly,Herbaspirillum sp.WT00C is able to synthesize?-linolenic acid,which is required by human body.Furthermore,Herbaspirillum sp WT00C also metabolizes certain aromatic compounds such as3-fluobenzene,4-fluobenzene,4-chlorophenol and thioformamide.Although no nif gene for nitrogen fixation was found in its genome,this bacterium can provide ammonia by using several ways such as amino acid metabolism,urea cycle etc.Genomic annotation also reveals that Herbaspirillum sp.WT00C has a pathway to synthesize indole acetic acid and siderophore.The amino acid sequences of the key enzyme nonribosomal peptide synthetase is a high degree?97%?of homology to that of H.seropediae.The molecular structure of siderophore predicted for Herbaspirillum sp.WT00C is the same as that reported for H.seropediae.In addition,Herbaspirillum sp.WT00C has a gene coding for ACC deaminase thought to be involved in modulating plant ethylene-signaling pathway and IAA action.Enzyme activity assay showed that ACC enzyme activity was 1.1?moL mg^-1h^-1.In the genome of Herbaspirillum sp.WT00C,many genes were found to encode glutathione,glucanase,peroxidase,trehalose etc.,which are relevant to osmotic pressures.Herbaspirillum sp.WT00C also synthesizes spermidine,folic acid,Vitamin B6 and B12 which have been thought to participate in physiological metabolism of plants.In the genome of Herbaspirillum sp.WT00C,multiple protein secretion systems including type I,type III,type IV,type IV pili,type V,and type VI secretion systems has been found.Especially,type IV secretion system only exist in the genome of herbaspirillum sp.WT00C,and other Herbaspirillum species do not have it.Those results obtained from this study lay solid fundation for us to fully understand the mechnism of plant-growth promotion of herbaspirillum sp.WT00C and its application in agriculture production.