A Comparative Study On The Evolution Of Different Photosynthetic Types In Salsola Genus

C4 photosynthesis is a photosynthetic pathway that facilitates the survival and growth of plants in the development of high temperature and drought stress conditions.Chenopodiaceae plants of the genus Salsola are widely distributed in Central Asia and are extremely drought tolerant.Salsola includes all three photosynthetic species,making it an ideal material for studying the adaptive evolution of photosynthetic carbon assimilation in desert plants.The paper studied the photosynthetic adaptive evolution of different photosynthetic Salsola species in desert habitats in Northwest China by comparing the physiological and biochemical characteristics of each Salsola species,DNA barcoding,and RNA-Seq technology,providing a unique perspective and theoretical basis for the restoration of desert vegetation.The paper obtained the following main results:(1)Based on DNA barcoding technology,phylogenetic trees was constructed and species identification and photosynthetic classification were conducted for 7 species of Salsola genus(Salsola abrotanoides,Salsola junatovii,Salsola arbusculiformis,Salsola laricifolia,Salsola arbuscula,Salsola orientalis,Salsola dshungarica).There was a small difference in the sequence of C4 plants Salsola arbuscula,Salsola orientalis,and Salsola dshungarica.The differences in photosynthetic patterns among C3 plant Salsola abrotanoides and Salsola junatovii,and C3-C4 plant Salsola arbusculiformis and Salsola laricifolia.Five barcodes can be used for the identification of different photosynthetic types,and the ITS and psbB-psbH sequences are very accurate for the identification of Salsola species.The ITS and psbB-psbH sequence can be used to align more sequences within the genus and the photosynthetic typing result is more detailed.A variety of species of Salsola and various barcode sequences are favorable materials for the study of photosynthetic evolution of Salsola species,which provides a reference value for the evolution of photosynthetic patterns of Salsola species based on DNA barcodes.(2)Based on the comparative transcriptome data of 7 species of Salsola,unigene annotation results are good,and the functional annotated results of Nr,COG and GO among 7 plants are consistent.Then the expression quantity of C4 photosynthetic genes was analyzed and the functional analysis of C4 photosynthetic key enzymes PEPC and NADP-ME was performed.The results showed that: C4 photosynthetic genes express higher in C4 Salsola,GDC-P gene expressed higher in C3-C4 Salsola,the 7 species of Salsola all contain PEPC-1,PEPC-2 and PEPC-4,of which PEPC-1 is C4 type PEPC,and the 774 th amino acid is serine instead of alanine,the NADP-ME gene encoding about 641 aa is C4 type NADP-ME.Photosynthetic key enzymes activity of PEPC and PPDK gradually increase in transition to C4 photosynthetic type.Based on transcriptomes,the evolutionary tree was constructed and the evolution direction of different photosynthetic Salsola species was analyzed.C4 Salsola orientalis and C4 Salsola dshungarica constitute a sister group,C3-C4 Salsola arbusculiformis and C3-C4 Salsola laricifolia constitute a sister group,and the sequence differences among the 3 species of C4 Salsola are small.The evolution direction of the photosynthetic type is from C3 to C3-C4 to C4,but the selective pressure analysis indicates that single copy homologous genes are not positively selected.(3)The leaf anatomy,seed external morphology,and stress-resistance physiological characteristics of C3 Salsola abrotanoides,C3-C4 Salsola laricifolia and C4 Salsola orientalis were compared,and it was found that compared with C3 Salsola abrotanoides,the C3-C4 Salsola laricifolia and C4 Salsola orientalis leaves gradually formed structural features adapted to drought from the external morphology and anatomical structure,And the seed propagation strategy also changes due to different seed sizes.C4 Salsola species has high photosynthetic capacity and it has the material basis for regulating the infiltration capacity through soluble sugars,thereby improving drought resistance.C3-C4 Salsola species is used to increase carbon sequestration by increasing nitrogen and phosphorus utilization efficiency.C4 Salsola species increases carbon sequestration by increasing nitrogen and phosphorus content.Compared to C3 Salsola abrotanoides,C3-C4 Salsola laricifolia and C4 Salsola orientalis are more adaptable to the barren environment.In summary,the study used DNA barcode technology to verify the accuracy of species collected from the wild,and further classified 7 species of genus Salsola into three photosynthetic types and subdivided C4 photosynthetic into NADP-ME and NAD-ME subtypes.The transcriptome data was used to verify the expression and functional analysis of photosynthetic related genes in Salsola species and the evolutionary direction of C4.Finally,the morphological structure and physio-biochemical adaptability were correlated with the C4 photosynthetic evolution confirmed from the perspective of DNA barcodes and RNA-Seq.