Comparative Transcriptomic Study On The Grazing Adaptation Of Stipa Grandis In A Typical Steppe In Inner Mongolia

Adaptation is the response of organisms to environmental changes.Under certain conditions,organisms have the potential to develop effective and unique adaptive strategies.Long-term grazing can cause trade-offs in morphological,physiological and biochemical characteristics of many steppe plants,and form plastic adaptive strategies to achieve survival and reproduction under the stress of continuous grazing.Stipa grandis is one of the dominant species in the typical steppe of Inner Mongolia,and plays an important role in the research on the response mechanism of grassland plants to grazing.In this study,S.grandis under long-time different grazing intensities was used as the research object.Based on the determination of their morphological changes,through transcriptome comparative analysis,the gene expression plasticity of the plant under different grazing stresses was quantified,and the information of cellular processes and metabolic pathways in response to grazing was understood.The differential gene expression patterns related to the Calvin-Benson cycle and photorespiration metabolic pathways were explored.This study analyzed the adaptation of S.grandis under different grazing treatments from a relatively new perspective,which will greatly promote the research on the grazing adaptation mechanism of this plant,and provide a scientific basis for selecting excellent forages carrying out reasonable grassland protection and utilization practice,and provide theoretical support for the improvement and restoration of the damaged grassland ecosystem.The main findings are as follows:（1）Under long-term grazing intensities,functional traits including vegetative branch height,reproductive branch height,canopy coverage leaf length,leaf area,leaf saturated fresh weight,specific leaf area,and leaf dry matter content of S.grandis showed different changing trends.The traits under grazing conditions showed an overall downward trend compared with non-grazing,and the significance increased with the grazing intensity.（2）By sequencing the transcriptomes of S.grandis under different grazing treatments,approximately 10 Giga base sequencing data were obtained,and constructed a transcriptome dataset containing 33,241 gene sequences,which laid a foundation for the further study of grazing adaptation mechanisms.（3）Under different grazing intensities,a total of 2,357 differentially expressed genes（DEGs）were identified（FDR≤0.001,|log₂（fold-change）|>1）.Functional enrichment analysis showed that these genes were significantly distributed in KEGG pathways of photosynthesis,carbon fixation in photosynthetic organisms,carbon metabolism,photosynthesis-antenna proteins,glyoxylate and dicarboxylate metabolism,etc.,and in GO term such as chloroplast,mitochondrial,response to high light intensity,and response to heat,etc.（4）114 genes encoding 11 enzymes in the Calvin–Benson cycle were identified.Among them,38 were DEGs,which showed the plasticity characteristics under different grazing intensities.For the DEGs of Rubiscos,GAPDHases,and Tkases,the expression levels of these transcripts from moderate grazing（MG）to heavy grazing（HG）were significantly increased;the DEGs of ALDases and SBPases were significantly down-regulated from no grazing（CK）to light grazing（LG）,relatively stable in LG to MG,and up-regulated in MG and HG.（5）121 genes encoding 12 enzymes in the photorespiration pathway,and 38 of which were DEGs.The DEGs of PGLPase,GOXases,GDCases（CL95.Contig34,CL95.Contig47）and GGTases were down-regulated in LG,up-regulated in MG and HG.The expression levels of GOXases（CL14974.Contig19,Unigene9650）and SGTases（CL593.Contig32）were up-regulated in MG and down-regulated in HG.（6）qRT-PCR validation showed that the gene expression plasticities of nine key genes in CBC and photorespiration pathway were consistent with the transcriptomic identifying in S.grandis samples collected in grazing experimental plots for two consecutive years（2018 and 2019）,although there were some differences between the years.