| Prunus avium is classified belonging to Prunus subgenus cerasus of Rosaceae,it is a perennial deciduous fruit tree.It is been called “The firstly ripening fruit in spring” for its earlier flowering date and ripening date than other fruits.Cherry fruit is rich in nutrition and has high economic value,widely cultivated in the world.Cherry industry has developed rapidly in China due to the remarkable economic benefits of sweet cherries.The planting areas have developed from Bohai bay to Northwest,Huaihai and Southwest of China,and become an important agricultural economic industry in these areas.However,the development of cherry industry is facing with many difficulties,among which drought is one of the most important abiotic stresses.Cherry growth,reproduction,uptake and transport of nutrient and water can be easily disturbed by drought,while cherry plants respond differentially to drought stress among species.Some cherry rootstocks(Prunus subgenus cerasus)showed diversity in drought resistance,while the molecular mechanisms of drought resistance remain unclear.Therefore,this work aimed to reveal the drought response mechanism of Prunus subgenus cerasus with contrasting drought resistance,i.e.resistant vs.sensitive,by comparing their differences in physiological,metabolic and molecular processes in response to drought stress.(1)Seven rootstocks were collected and investigated with their biological backgrounds as P.tomentosa,P.pseudocerasus,P.cerasus×P.canescens,P.pseudocerasus× P.avium,P.mahaleb and P.mahaleb ×P.fruticosa,respectively,which were originated from different areas and varied in drought resistance.Drought resistance was evaluated by membership function method based on physiological indexes responded to drought.Relative water content of leaves(RWC),ChlorophyII content,proline(Pro)content,malondialdehyde(MDA)content,peroxidase(SOD)content,superoxide disulfide enzyme(POD)and oxidase(CAT)content were used as evaluation indicators.Drought resistance index was calculated for each rootstocks.Drought reistance of rootstocks was evaluated based on phenotype injured dgrees of each rootstocks and drought resistance index.Seven genotypes ranked from resistant to sensitive as following: ‘CDR-1',‘CDR-2',P.tomentosa,‘Gisela 6',‘Colt',‘Daqingye',‘Gisela 5'.(2)Photosynthetic gas exchange and chlorophyII fluorescence parameters of the seven rootstocks were measured under drought stress to analysis the common and differential photosynthetic response characteristics of each rootstocks.Photosynthetic rate(Pn),intercellular carbon dioxide concentration(Ci),stomatal conductance(Gs),transpiration rate(E),water use efficiency(WUE),actual photochemical efficiency(? PS ?),photochemical quenching coefficient(qP)and non-photochemical quenching coefficient(NPQ)were detected.Seven rootstocks showed difference photosynthetic capacity under severe drought conditions(SRWC35%40%).The inhibition of photosynthetic efficiency of‘Gisela 5' and P.tomentosa was more severe under drought conditions than the other rootstocks.The minimum SRWC content for cherry rootstocks should be greater than SRWC40%.The optimum SRWC for cherry rootstocks was 60% to 80%,The greatest WUE and photosynthetic efficiency of cherry rootstocks was achieved in this condition.The results of photosynthetic index analysis showed that ‘Gisela 6',‘CDR-2',‘CDR-1'‘Colt' and ‘Daqingye' had stronger regulatory ability under severe drought than ‘Gisela 5'and P.tomentosa in severe drought conditions.(3)Comparative transcriptome and metabolomics analysis was conducted to investigate key genes and metabolites involved in drought responses with contrasting drought resistance cherry rootstocks(drought resistant genotype ‘CDR-1'and drought sensitive geneotype ‘Gisela 5').Drought responded differential expressed genes(DEGs)were selected based on RNA-Seq analysis: 281 and 626 DEGs were up and down regulated in ‘CDR-1' leaves,respectively,while 84 up and 1079 down DEGs in ‘CDR-1' roots;79 up regulated and 400 down regulated DEGs were detected in ‘Gisela 5' leaves,while71 up regulated and 205 down regulated DEGs were detected in ‘Gisela 5' roots.Drought responded differential metabolites were selected based on non-target GC-MS method: 234 drought responded differential metabolites were selected from cherry rootstocks,92 metabolites were up regulated among them.There were 59 up regulated metabolites specific in ‘CDR-1',19 up regulated metabolites were specific in ‘Gisela 5',14 common differential metabolites accumulated in both rootstocks.Up regulated metabolites are mainly organic acids,purines,lipids,amino acids,nucleotides,carbohydrate derivatives and alkaloids,etc.It was found that carbohydrate metabolism,signal transduction of plant hormones and plant secondary metabolites were most responded pathways,they were closely related to the drought responses of cherry rootstocks according to combined analysis of transcriptomic and metabolomics results.The differential genes and metabolites involved in phenylpropanoid biosynthesis pathway and Cyanoamino acid metabolism pathway are the key factors leading to drought resistance difference between the two rootstocks,the metabolic pathways of “quinic acid?phenylalanine?P-Coumaric acid” and “quinic acid?phenylalanine? 3-cyanoalanine? asparaginamide” were occured in ‘CDR-1',while“quinic acid ? caffeic acid?chlorogenic acid” and “quinic acid ? phenylalanine ?3-cyanoalanine ? asparagine” were occured in ‘Gisela 5'.Moreover,accumulation of quinic acid,phenylalanine,3-cyanoalanine and asparagine on ‘CDR-1' and ‘Gisela 5' was183.0,1.3,4111229.0,7.0 and 1.5,1.2,2.1,2.6 times,respectively.The results showed that protective metabolites synthetic efficiency and cyanide detoxification efficiency of‘CDR-1' was higher than that of ‘Gisela 5',which may cause the difference of their drought resistance.Six key drought response differential metabolites including quinic acid,phenylalanine,3-cyanoalanine,asparagine,p-benzoquinone and phytosphingosine were identified in cherry rootstocks.Based on GO,KEGG analysis and PPI interaction network analysis of DEGs and conjoint analysis of differential metabolites and DEGs results,17 core candidate genes was selected including 4 genes involved in energy metabolism,3ubiquitin ligase genes and 1 zinc finger gene,etc.,and the basic biological information analysis of these genes was carried out.Finally,comprehensive analysis was made with the physiology,transcriptomic and metabolomic test results,and hypothetical drought responded mechanism of ‘CDR-1' was summarized. |
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