Screening Of Drought-tolerant Germplasm From Chrysanthemum And Related Genera And Identification Of Drought Responsive Genes

Chrysanthemum × morifolium is one of the most important ornamental crops in the world,and drought stress is one of the main factors limiting its production.However,there are a lot of germplasm with strong drought tolerance in Chrysanthemum and related genera,such as Opisthopappus taihangensis and so on.These germplasm not only have strong drought resistance,but also have other good traits,such as wind resistance,disease resistance.According to the data of cultivation from our research team,drought tolerance of four materials from generalized Chrysanthemum species was studied,including Chrysanthemum lavandulifolium,Chrysanthemum indicum,Ajania fruticulosa,Opisthopappus taihangensis,which were put under 20%PEG6000 for progressive stress.According to the morphological index,physiological index and photosynthetic index of four germplasm under drought stress,Opisthopappus taihangensis was the best germplasm for drought resistance.With the endogenous ABA index and photosynthetic indexes of Opisthopappus taihangensis,we chose 3.5 hours as an important point-in-time under drought stress and analyzed the transcriptome of high-throughput sequencing and bioinformatics.The main results were as follows:(1)According to the preliminary screening of germplasm evaluation data,Chrysanthemum X lavandulifolium,Chrysanthemum indicum,Ajania fruticulosa and Opisthopappus taihangensis was selected as experimental materials.According to the morphological index and physiological index(Pro,cl,chl)and photosynthetic indexes(Pn,Tr,Cd),we evaluated the drought resistance of the above 4 germplasm under 20%PEG6000.The results showed that the change rate of Opisthopappus taihangensis in each index was relatively small,and the changes in cells were relatively stable.Through the statistics of the experimental data,we found that Opisthopappus taihangensis was the best drought resistant germplasm.The endogenous ABA of Opisthopappus taihangensis was measured and combined with photosynthetic index,3.5 hours stress was selected as an important time node for early drought response of Opisthopappus taihangensis.(2)Transcriptome sequencing of the leaf samples of Opisthopappus taihangensis under 20%PEG6000 drought stress Oh and 3.5h,and each sample were divided into three biological repeats.In this study,135701 of Unigene were tested and the total length of Unigene was 123652254bp,and the corresponding functional annotation information of Unigene were obtained in different databases.Analysis of gene expression levels to readcount data,a total of 14599 differentially expressed genes(DEGs)(Padj)(<0.05)were observed.Among them,8467 genes were up-regulated and 6488 genes were down regulated.GO enrichment analysis showed that the metabolic process and cell processes were most abundant in DEGs.KEGG Pathway analysis showed that the number of differentially expressed genes such as plant hormone signal transduction,ABC transportation,starch and sucrose metabolism,biosynthesis of flavonoids and arginine and proline metabolism were relatively high.(3)Under drought stress of 20%PEG6000,MYC,WRKY,MYB,serine/threonine protein kinases and other gene family were the earliest response to drought stress at 3.5h.Moreover,the expression of the kinase related to trehalose metabolism and Ca related Pathway was also up-regulated,which showed they have a close relationship with the drought resistance.The metabolic pathways,associated with drought in the ABA signaling pathway and proline metabolism pathway,positively responsed to drought stress.Many secondary metabolites biosynthesis related genes in a large number of lower secondary metabolites synthesis were inhibited,and the genes related to carbohydrate metabolism pathways in part began to cut down the process of synthesis and glucose metabolism of the secondary metabolites,which is one of the drought stress response of Opisthopappus taihangensis.(4)Results of qRT-PCR were in line with transcriptome data.We randomly chose 12 differential expressed genes for qRT-PCR analysis.At the same time,it was possible to screen out the important genes in the early response to drought stress,such as transcription family:WRKY25,MYC2,kinase:FLS,PBS1,BAK1,and AA03,NCED gene in the ABA metabolic pathway.In summary,Opisthopappus taihangensis showed high resistance to drought with its photosynthetic and physiological indexes were stable under drought stress;And it was found that Opisthopappus taihangensis responses to drought stress by the regulation of plant hormone signaling,reduce energy consumption and stable cell structure.A series of important genes were excavat ed,which laid a foundation for future breeding of chrysanthemum resistance to drought.