Exploration And Functional Analysis Of Endophytic Bacterial Resource In Wetland Plants

Wetland is a special ecosystem formed by interaction between water and land on earth.Water purification by the combination of plants and microorganisms in wetland can effectively improve the regional ecological environment quality.Endophytic bacteria in wetland plants can often positively influence host plant growth and enhance adaptation to environment.They play an important role in the maintenance of ecosystem balance.In this study,two kinds of wetland plants,common reed(Phragmites australis)and narrowleaf cattail(Typha angustifolia L.)were studied.The micropropagation systems using regeneration of common reed and narrowleaf cattail had been constructed.The bacterial communities in the rhizosphere,root endosphere,and seeds of mature,natural common reed and narrowleaf cattail were investigated using Illumina-based sequencing.Regenerated reed plantlets were inoculated with activated sludge containing abundant microbial groups to explore the unique,diverse,and functional endophytic bacteria.The propagation of plant tissue in vitro with the functional endophytic bacteria for improving wetland plant quality was studied.The main contents and results were as follows:(1)The micropropagation systems using regeneration via somatic embryogenesis from mature seeds of common reed and via organogenesis from mature seeds of narrowleaf cattail had been constructed.Proliferating reed embryogenic cultures possessing strong differentiation potential to produce somatic embryos were chosen as the propagules.These high-potential embryogenic cultures were capable of rapidly producing uniform plantlets and providing an ideal experimental method for endophytic root colonization under controlled conditions.(2)Obvious distinctions were observed among the respective rhizospheric,root endophytic and seed endophytic bacterial communities of mature,natural common reed and narrowleaf cattail.Seed endophytic bacterial communities were distinct assemblages rather than a subgroup of rhizobacterial communities or root endophytic bacterial communities.Seed endophytic bacterial communities were dominated by Proteobacteria,followed by Bacteroidetes,Planctomycetes,Chloroflexi,Thermotogae,Tenericutes and Spirochaetes.The dominant genera were Desulfobacter,Geobacter,Thiobacillus,Sulfurimonas,Methyloversatilis and Dechloromonas.(3)Regenerated plantlets of common reed were inoculated with activated sludge to obtain the specific functional endophytic bacterium.Denaturing gradient gel electrophoresis(DGGE)analysis demonstrated that abundant endophytic bacteria could be enriched in the roots of reed after inoculation with activated sludge.Eleven different endophytic strains,including Novosphingobium sediminicola RE3-1,Rhizobium tubonense RE3-2,Herbaspirillum frisingense RE3-3,Leifsonia naganoensis RE3-4,Rhodococcus fascians RE3-5,Staphylococcus warneri RE3-6,Chryseobacterium rhizosphaerae SHI,Delftia lacustris SH2,Achromobacter xylosoxidans SH4,Serratia nematodiphila SH5 and Staphylococcus epidermidis SH6 were isolated from the roots of reeds.(4)The endophytic bacterium Achromobacter xylosoxidans SH4 expressed high resistance to lead.It showed that the maximum biosorption capacity was 57.94 mg g-1.Production of extracellular polymeric substances(EPS)can bind the metal,perhaps making the microenvironment around the plant less toxic.(5)The endophytic bacterium Herbaspirillum frisingense RE3-3 can secretes indole-3-acetic acid to promote plant growth and cadmium-binding siderophores.The strain was successfully colonized into synthetic seeds using bacterium-propagule co-cultivation and transmitted to regenerated seedlings.These seedlings exhibited improved growth under cadmium stress.This study identifies Herbaspirillum colonization and transmission as a potentially valuable strategy to improve the phytotoxin resistance of reeds.In this study,the technologies of plant cell engineering and molecular biology were used to explore the excellent resource of endophytic bacteria in wetland plants.The mechanisms of heavy metal tolerance and plant growth promotion in the functional endophytic bacteria were analyzed.The functional endophytic bacteria were further applied to wetland plant breeding using bacterium-propagule co-cultivation,which provides a potentially valuable strategy to breed improvement of wetland plants.