| As a common natural disaster in the process of plant cultivation and introduction,low temperature stress often causes great losses to plant survival and local production.Xanthoceras sorbifolia is a unique and excellent woody oil tree species in China,which has strong low temperature resistance characteristics,It is a rare ideal material to study the mechanism of plant cold resistance.Therefore,the study on the physiological regulation mechanism of the response of Xanthoceras sorbifolia to low temperature stress is not only conducive to the gradual improvement of the theoretical system of plant cold tolerance,but also lay the foundation for the cold resistance improvement breeding of Xanthoceras sorbifolia.In this study,we mainly measured the dynamic changes of 15 physiological indexes of Xanthoceras sorbifolia seedlings under low temperature stress,and combined with the changes of metabolite content,preliminarily showed the material change network of Xanthoceras sorbifolia seedlings in the process of adapting to low temperature.At the same time,the transcriptome analysis under low temperature stress revealed the internal relationship between gene expression and low temperature stress of Xanthoceras sorbifolia.The purpose of this study was to explore the response of Xanthoceras sorbifolia to low temperature stress and the mechanism of cold resistance from physiological level,metabonomics and transcriptomics.The main results are as shown below:1.The 30 day seedlings of Xanthoceras sorbifolia were used as experimental materials.We used the method of artificial temperature control in constant temperature incubator.The culture temperature was 25℃as control,4 ℃ as low temperature stress temperature,and the duration of stress was 4h,12 h,24h and 48 h.The contents of Osmoregulation Substances,accumulation of harmful substances,photosynthetic characteristics and protective enzyme activity of seedlings were determined Time changes.The results of variance analysis,correlation analysis and principal component analysis showed that malondialdehyde,osmoregulation substance content and intercellular CO2 concentration continued to increase under 4 ℃ low temperature stress.However,relative water content,photosynthetic rate and other photosynthetic characteristics was decreased;the cumulative contribution rate of two independent comprehensive indexes to15 physiological indexes reached 85.649%,the comprehensive score of membership function calculation was0h>12h>24h>4h>48h.The change trend of the resistance to low temperature stress of Xanthoceras sorbifolia seedlings with the duration of low temperature is from lower to higher to lower.2.GC-TOF-MS,LECO fiehn rtx5 database matching,P value of student’s t test and VIP value of opls-da model were used to analyze the metabonomics of 12 h stress duration and control Xanthoceras seedlings.Through the differential screening and qualitative analysis of metabolites,117 differential metabolites were screened out,including 68 up-regulated metabolites and 39 down-regulated metabolites,38 of which were qualitative;the main up-regulated substances were Xanthosine,lactulose1,beta-Mannosylglycerate 1,sorbitol,Linoleic acid methyl ester,etc.the main down-regulated substances were4-Hydroxyphenylethanol,Lactobionic Acid 1,Epigallocatechin,alpha-ketoisocaproic acid 1,citric acid,etc.It is mainly enriched in 34 metabolic pathways.The increase of amino acid and carbohydrate contents can improve the osmotic adjustment ability of Xanthoceras sorbifolia,while the accumulation of sucrose and the decrease of citric acid content can lead to the decrease of photosynthesis.3.RNA SEQ was used to sequence the transcriptome of the leaves of Xanthoceras sorbifolia seedlings and the control plants for 12 hours under stress.A total of 49.25 Gb clean data was obtained,and the percentage of Q30 base of all varieties was no less than 93.82%.After the assembly and annotation of the sequenced clean reads,63,197 unigenes were obtained,of which 27,219 were annotated.1,154 differentially expressed genes,including 723 up-regulated genes and 431 down-regulated genes,were screened out from Xanthoceras sorbifolia seedlings under low temperature stress.The results of GO and KEGG enrichment showed that there were many low temperature response pathways in Xanthoceras sorbifolia.According to the prediction of transcription factors,ERF and WRKY have more gene expression changes in 57 up-regulated expressions,indicating that these transcription factors play an important role in regulating the expression of cold response genes.These studies provide a theoretical basis for elucidating the molecular mechanism of cold resistance of Xanthoceras sorbifolia. |
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