Study On Photosynthetic Characteristics And Adaptive Evolution Of Chloroplast Genome In Dendrobiu

Dendrobium,the second largest genus of orchidaceae,Its design and color is bright and beautiful,posture is elegant myriad,have very high horticultural view and admire value.In addition,according to the book of shennong materia medica,Dendrobium has the effect of "producing fluid to quench thirst,nourishing Yin and benefiting stomach",so it has high medicinal value.In recent years,the wild resources of Dendrobium are on the verge of exhaustion due to the destruction of ecological environment and people’s indiscriminate mining and digging.Therefore,Dendrobium has important research value.Since the origin of the Dendrobium,in order to adapt to a series of changes in the ecological environment,such as the decrease of water content and carbon dioxide concentration,Dendrobium has evolved rapidly,so a variety of photosynthetic pathways have been formed among its species,such as C3,facultative CAM and obligate CAM.However,the molecular mechanism of the formation of different photosynthetic pathways in adaptation is not yet clear.In this study,the photosynthetic indexes of 13 Dendrobium species were determined,it was found that Dendrobium primulinum、Dendrobium terminale、Dendrobium spatella and Dendrobium changjiangense are CAM plants.Dendrobium nobilis,Dendrobium hercoglossum and Dendrobium officinale are C3-CAM plants.Dendrobium thyrsiflorum、Dendrobium chrysotoxum、Dendrobium chrysanthum、Dendrobium williamsonii、Dendrobium longicornu and Dendrobium lindleyi were C3 Dendrobium plants.Based on phylogenetic analysis,it was found that CAM plants were not clustered into one branch,indicating that CAM photosynthetic pathway originated independently in Dendrobium and had nothing to do with kinship.In addition,47 variable shear events were found in pepc gene through the analysis of three generations of transcriptome data,suggesting that the variable shear events may promote the transformation of photosynthetic pathway in Dendrobium and lead to enhanced photosynthesis.High-throughput sequencing technology was used to sequence D.thyrsiflorum and D.densiflorum,and complete chloroplast genome sequence was obtained by splicing.Based on comparative chloroplast genome analysis,it was found that the structure,gene composition and number of chloroplast genome of D.thyrsiflorum and D.densiflorum were relatively conservative,m VISTA was used to compare D.thyrsiflorum,D.densiflorum and D.officinale,the differences were found mainly in non-coding regions.Based on the locus model,the selection pressure of chloroplast protein-coding genes in Dendrobium was analyzed,found that there were 10 genes in total,such as acc D,mat K,psb H,rbc L,rpl2,rpl16,rpo A,rpoc1,rpoc2,and ycf2.This study further investigated the adaptive evolution of chloroplast genes in Dendrobium.Build rpo C2 evolutionary tree,through the site model calculation,found that C3 plants D.chrysotoxum and D.chrysanthum affected by are choosing,are choosing sites for: 470 T,516D,619 I,874R and 1014 H,further found that four site for parallel evolution site,through the analysis of C3 plants D.chrysotoxum rpo C2 gene protein three-dimensional structure,finding adaptive evolution of five sites near the function structure domain,showed that plants of the genus Dendrobium stem in C3 to CAM these sites play an important role in the process of evolution.In conclusion,through the study on the photosynthetic characteristics of Dendrobium and the adaptive evolution of chloroplast genome,this paper revealed that the transformation of photosynthetic pathway of Dendrobium was related to the parallel evolution of photosynthetic genes,which laid a foundation for further study on the transformation of photosynthetic pathway.