Study On The Mechanism Of Low Temperature Improving The Quality And Physiological Response Of Lonicera Japonica

Lonicera japonica（L.japonica）is a traditional medicinal plant in China,the whole plant can be used as medicine,with antibacterial,antiviral,antitumor and other pharmacological effects.In recent times,the flowers are mainly used as medicine,but the flowering period is limited and the harvesting period is short,while L.japonica leaves have similar efficacy components to the flowers,and the yield is high and not limited by time.Some studies have demonstrated that chilling stress can induce anthocyanin accumulation in L.japonica leaves,but the effect of low temperature on other secondary metabolites has not been revealed.In this study,we systematically investigated the molecular mechanism of L.japonica leaves in response to chilling stress through physiological index determination,index component determination and comparative transcriptome analysis,the main conclusions are as follows:1.L.japonica leaves gradually changed from green to purple under chilling stress.Malondialdehyde,soluble sugar and soluble protein accumulated significantly,and superoxide dismutase（SOD）,catalase（CAT）and peroxidase（POD）activities showed a trend of first increasing and then decreasing or unchanged,indicating that L.japonica leaves mitigate the damage caused by low temperature by accumulating osmoregulation substance and activating antioxidant enzyme systems.2.The gene expression profiles of L.japonica leaves at 0（SP）,15（T15）and 30days（T30）under chilling stress were analyzed by transcriptome sequencing technique,and a total of 9 c DNA libraries were constructed,obtaining 65.89 Gb of Clean bases.3715 and 3834 differentially expressed genes（DEGs）were identified at T15 and T30in L.japonica leaves,respectively.The KEGG enrichment analysis of DEGs showed that these DEGs were mainly involved in starch and sucrose metabolic pathways,photosynthesis-related protein pathways and hormone signaling pathways.Analysis of the expression trends of DEGs on related pathways showed that the absorption of light energy by L.japonica leaves was reduced and photosynthesis was inhibited under chilling stress.Alpha-amylase（AMY）and glucose phosphate metastase（PGM2）help L.japonica leaves to resist low temperature by increasing the content of maltose and glucose 6-phosphate,respectively.Brassin-osteroid（BR）and its signal transduction pathway may play a key regulatory role in the cold domestication of L.japonica leaves.3.The molecular mechanism of low temperature-induced leaf color changes in L.japonica was investigated by analyzing the pigment content and pigment synthesis-related pathways in L.japonica leaves at SP,T15 and T30,with the following main results:The chlorophyll content did not change significantly as a result of the dynamic balance between chlorophyll synthesis and degradation;Most genes related to carotenoid and anthocyanin synthesis were up-regulated in expression,resulting in their significant accumulation;Low temperature induces leaf color changes in L.japonica by reducing the percentage of chlorophyll content and increasing the percentage of carotenoid and anthocyanin content.Genes that maintain Ca²⁺homeostasis and Ca²⁺channel protein genes are up-regulated under chilling stress.4.HPLC was used to quantify the indicator components in L.japonica leaves under chilling stress and to investigate the mechanisms of molecular changes,with the following main results:Both chlorogenic acid and luteoloside content were significantly increased and most of their biosynthesis-related genes（PAL,C4H,4CL,CHS,F3’H,etc.）were up-regulated in expression.ERF,b HLH and MYB family transcription factors significantly respond to low temperature in L.japonica leaves.MYB12,which positively regulates the synthesis of flavonoids and phenolic acids,was up-regulated in the MYB family;while MYB44,which negatively regulates the synthesis of flavonoids and phenolic acids,was down-regulated.In summary,this study found that the antioxidant system in L.japonica leaves was activated at 10°C,and the change in the ratio of chlorophylls,carotenoids and anthocyanins resulted in a change in color from green to purple.In addition,indicator components such as chlorogenic acid and luteoloside also accumulated significantly,and the molecular mechanism of the above physiological changes was further analyzed by comparative transcriptomics,thus providing a new idea for improving the ornamental and medicinal values of L.japonica leaves.