| Pear,as an important fruit tree resource in our country,has an extremely high economic value.Jin Guang flower early in spring,and the floral organs are vulnerable to late frost hazards,resulting in lower yields and unfavorable for pear industry development.In this study,flower organs were treated with cold temperatures mimicking cold conditions in a frost box,and browning assays as well as over cooling point,electrical conductivity(REC),soluble protein(SP),malondialdehyde(MDA),catalase(CAT),and superoxide dismutase(SOD)activities were performed at the temperatures of 18℃(CK),2℃(CT1),0℃(CT2),2℃(CT3),and 4℃(CT4),Transcriptome sequencing was performed on floral organs of ’Jin guang’ to explore the molecular mechanism of cold tolerance in ’Jinguang’ flower organs,and to provide a theoretical basis for mining relevant cold resistance genes and nurturing cold tolerant pear cultivars.The main findings were as follows:1.Under chilling stress treatment,the 5 test material flower organs had the heaviest browning degree at-4℃;The supercooled point for "" golden light "" flower organs is5.7℃;The electrical conductivity and malondialdehyde content significantly increased with the increasing degree of chilling stress.The soluble protein content,catalase and superoxide dismutase activities showed an initial increase and then a decrease,all of which reached their maximum values under CT2 treatment,indicating that CT2 treatment increased the activities of antioxidant enzymes and promoted the synthesis of osmoregulatory substances.According to comprehensive relevant physiological indexes,the tolerance to low temperature of ginseng organs was obtained by principal component analysis as "" HG051102 "">"" Mei Yu "">"" Jin Guang "">"" 041057 "">""SJ051105 "".2.A total of 11 846 significantly differential genes were identified during chilling stress in the ’Jin Guang’ flower organ by transcriptome sequencing.The number of up-regulated genes was significantly higher than that of down regulated genes in four different comparison groups:CT1,CT2,CT3 and CT4.Among them,there were 1 067 DEGs(890 upregulated and 177 downregulated)in CT1,6 378 DEGs(3 483 upregulated and 2 895 downregulated)in CT2,2 872 DEGs(1 608 upregulated and 1 264 downregulated)in CT3 and 1 529 DEGs(844 upregulated and 685 downregulated)in CT4.The DEGs were mainly enriched in the pathways of photosynthesis,circadian rhythm,and flavonoid biosynthesis.Low temperature stress causes significant up regulation of gene expression in energy metabolism and flavonoid biosynthesis,which may directly affect physiological processes such as cell growth,metabolism and enzyme activity in response to low-temperature stress.3.The DEGs under chilling injury treatment(CK and CT1 and CT2)were mainly enriched in the metabolic function and binding function related GO terms,while under chilling injury treatment(CK and CT3 and CT4),the DEGs were mainly enriched in the catalytic function related GO terms.All KEGG pathways were enriched in several biological processes,such as metabolism,flavonoid biosynthesis,photosynthesis antenna proteins,circadian rhythm,biosynthesis of secondary metabolites,and nitrogen metabolism.There were also some specific pathways between the two comparison groups,for example,starch sucrose metabolism and fructose mannitol metabolism pathways existed only in the chilling injury comparison group,and Zeatin biosynthesis as well as steroid biosynthesis pathways existed only in the chilling injury comparison group.4.Weighted gene co expression network analysis(WGCNA)showed a strong association between specific gene modules and MDA(1 module)as well as with soluble proteins(1 module),and functional annotation of the differently expressed hub genes in these modules indicated that they function to regulate signaling,enzymatic activity,metabolic activity,transcription factors and so on and can effectively defend against cold environments.The key enzyme NPC1,the transcription factor MYB102,and the BBX19 gene as well as the LHY gene are located at the heart of the constructed network and have important potential roles under chilling stress. |
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