| Low temperature is one of the key climate and environmental factors.Identification of low temperature-related genes can provide insights into the adaptation mechanism of plants to low temperature stress.Forsythia suspensa is an excellent garden ornamental plant and bulk medicine.Although its adult plants have high cold resistance,the seedlings are often injured by low temperature.Based on the results of previous landscape genomics research,we performed physiological index detection,transcriptome sequencing,and landscape genome re-analysis of F.suspense under low temperature stress,and comparative analysis of the relationship between the cold adaptation genes of "long-term memory" and the cold response genes of"transient memory" of F.suspense was conducted to explore the adaptation mechanism.The results are as follows:(1)Physiological and transcriptome level response of F.suspensa to low temperature stressThe increase of relative conductivity and MDA content showed that the membrane system of F.suspensa was damaged by cold stress.In response to the decrease of cellular osmotic pressure caused by the destruction of membrane system,osmotic regulatory substances,including SS,Pro,and SP,increased significantly.The rapid increase of SS and Pro and the subsequent decline indicate that they are an emergent response to regulate the cellular osmotic pressure,while the stability of SP after the rapid increase indicates that it plays a more important role in the process of the regulation of cellular osmotic pressure.The significant increase of SOD and POD of F.suspensa also indicated that the ROS scavenging mechanism was activated to cope with cold stress.The decrease of chlorophyll content indicated that in addition to the influence of cold stress on the membrane system,chlorophyll synthesis was also significantly inhibited,thus reducing the efficiency of photosynthesis.Transcriptome sequencing was performed on seedlings of F.suspensa in different treatments.A total of 90.73 Gb of Clean Data was obtained,and the Clean Data of each sample reached 5.89 Gb.The Oh vs 3h,Oh vs 6h and Oh vs 12h comparison groups contain 69,131,and 305 up-regulated differentially expressed genes and 3,5 and 26 down-regulated differentially expressed genes.The CRGs provided a considerable amount of information on the response of F.suspensa to the transient cold stress.Under the transient cold stress,F.suspensa initiated a series of programs,increasing cell osmotic pressure by synthesizing SS,SP and Pro,scavenging ROS by SOD,POD and phenolic compounds,Closing the stomata,increases the rigidity of the cell wall,activating the defense mechanism that cross with pathogen infection,and further initiating the downstream cascade reactions,to cope with this stress.Meanwhile,the circadian rhythm was broken,and the photosynthesis was inhibited.(2)Reanalysis of the results of landscape genomics researchIn previous landscape genomics studies,SNPs identified by the LFMM method were considered as environmentally relevant sites.As a result,1,216 cold-adaptive genes closely related to the PC1 axis were identified.Among these candidate cold-adaptive genes,391 and 630 genes were annotated by KEGG and GO databases,respectively.Compared with the CRGs after 12h cold stress,13 genes overlap,and all of them are up-regulated genes.The results reanalysis of previous landscape genomics study suggested F.suspensa responded to the long-term heterogeneous cold stress by the differentiation of genes related to the synthesis of aromatic substances and adenosine triphosphate.The comparative results supported the the hypothesis,i.e.,the adaptation mechanism of species to short-term environmental stimulation and differential long-term stress in heterogeneous environments is different,and the EAGs are not necessarily ERGs.Overall,this study provides new insights into the adaptation mechanism of plants in response to transient and long-term differential cold stresses. |
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