Effects Of Trichoderma Asperellum And Alternaria Alternata On Photosynthetic Characteristics And Related Gene Expression Of Populus Davidiana × P. Alba Var. Pyramidalis

In order to reveal the mechanism of Trichoderma asperellum promoting the growth of woody plants and improving their disease resistance,a series of experiments were designed.In this study,tissue culture seedlings of Populus davidiana ×.alba var.pyramidalis(Shanxin poplar)were used as materials.Untreated Shanxin poplar seedlings were used as control group.In experimental groups,there were different handles including that the roots(R)were inoculated with.asperellum(T,probiotics),the functional leaves(L)were infected with Alternaria alternata(A,pathogenic fungi),and both together(TA)for 2 days.To obtain the expression regulating characteristics of photosynthesis related genes,36 transcriptome databases were constructed with the materials of stem tip,functional leaves infected with A.alternata and roots.Subsequently,the treated tissue culture seedlings were transplanted into the soil for 60 days.It was found that tissue culture seedlings of Shanxin poplar interacted early with the two fungi had an effect on their subsequent growth and photosynthetic characteristics,according to the results of growth traits observation,physiological indicators detection,photosynthetic characteristics analysis,and gene expression regulation.The main results were as follows:1.Through transcriptome comparative analysis,657 genes involved in photosynthesis were obtained,including 422 annotations existed in 18 categories of COG database;655 sequences classified into 52 functional categories of GO database;439 annotations in 16 pathways of KEGG database.On the other hand,70,95 and 140 genes expressed differentially were obtained from shoot tips,leaves and roots,respectively.They were mainly annotated in the photosynthesis and photosynthesis-antenna protein pathway of KEGG database.The results of qRT-PCR revealed that the expression patterns of most genes were consistent with that of these genes in transcriptome database.2.The relative expression levels of the genes in leaves,including PdpapLhcal,PdpapLhca2,PdpapLhcb1,PdpapPsbP,PdpapPsbW,PdpapPsb27 and PdpapPsaL were up-regulated than those in CK group induced for 2 days,while expression level of PdpapPetF was down-regulated.The relative expressions levels of PdpapPsbP,PdpapPsb W,PdpapPsb27 and PdpapLhcbl were up-regulated in group T,indicating that.asperellum could enhance the stability of plant photosynthetic system Ⅱ and increase the content of chlorophyll b.Photosynthetic related genes involved in photosystem Ⅱ were down-regulated in group A.On the other hand,the expression levels of PdpapLhcbl,PdpapPsbP,PdpapPsbW,PdpapPsb27 in group TA were up-regulated than those in group A,which revealed that T.asperellum alleviated the damage of A.alternata to plant photosystem and enhanced resistance of Shanxin poplar against to pathogens.3.The photosynthetic pigment,photosynthetic index and chlorophyll fluorescence parameter index of the soil culture transplanted seedlings were changed.All the indexes of Amax,AQE,Cond,Ci,qP,NPQ,φpPSII,and φNPQ in leaves of group T increased,which indicated that T asperellum could improve the photosynthetic ability of plants and the utilization rate of weak light,and enhance the activity of photosystem Ⅱ.At the initial stage of inoculation with A.alternata,photosynthetic pigments and Amax,Cond,Ci,Tr,qP and NPQ decreased,indicating that they had a negative effect on the photosynthetic capacity,functioning tissue and PSⅡ system of Shanxin poplar.4.When inoculated with funngi for 2 days,the results of physiological indexes showed that the content of malondialdehyde was TA>A>T>CK,and the content of soluble sugar was TA>A>CK>T.It meant apparently that A.alternata and.asperellum had also a bad effect on the cell membrane of the leaves of Shanxin poplar.Importantly,the damage of leaf cells was more obvious when the two fungi interacted together.After 60 days of transplantation,the indicators of Shanxin poplar in group T and group TA showed stable performance.The heights of Shanxin poplar were T>CK>TA>A.The fresh weights of leaf biomass were T>TA>CK>A.The fresh weights of stem were T>TA>CK>A.The fresh weights of root biomass were T>A>TA>CK.It indicated that.asperellum could improve plant growth,accelerate the accumulation of organic matter,and reduce the damage of A.alternata to plants.