Physiological And Molecular Responses Of Two Genotypes Of Pear To Drought Stress

Drought stress seriously limits the growth and development of pear trees,thus resulting in the decrease of crop yield and fruit quality.In order to better understand the drought-tolerance mechanism in pear plant,provide relevant experimental basis for breeding drought-tolerant pear tree cultivars,The responses to soil drying and rewatering were measured at morphological and physiological levels in plants of the two pear cultivars,including drought-tolerant Pyrus bretschneideri × P.pyrifolia’Huangguan’(HG)and drought-susceptible P.pyrifolia ’Niitaka’ × P.pyrifolia’Nijisseiki’ ’Whangkeumbae’(HK)pear plants grown in phytotron.To deeply elucidate the molecular mechanisms regarding pear plants response to dehydration,leaves were randomly collected at the middle portion of the shoot of ’Huangguan’ pear non-drought control(HGC),’Whangkeumbae’ pear non-drought control(HKC),Huangguan’ pear with simulated drought(HGSD),and ’Whangkeumbae’ pear with simulated drought(HKSD)were sampled and used for RNA-sequencing(RNA-Seq)analysis based on morphological and physiological changes.Additionally,the key enzyme genes for abscisic acid(ABA)synthesis and signal transduction in pear plant were cloned.The main results of this dissertation are as follow:1.Relative Water content of leaves(RWC),chlorophyll content(SPAD),net photosynthetic rate(Pn)and maximum photochemical efficiency(Fv/Fm),malondialdehyde(MDA),Proline(Pro)content and peroxidase(POD)activity increased significantly with drought stress and decreased rapidly after rehydration.Abscisic acid(ABA)and jasmonate(JA)reached rapidly to the peak at severe drought stress,then fell the normal level after rehydration.The auxin(IAA)decreased gradually with drought,then increased after rehydration.The(BR)of Brassinosterol increased suddenly in mild drought,decreased rapidly in severe drought,and increased slightly after rehydration.The fall rage of RWC,SPAD,Pn and Fv/Fm in HG leaves was smaller,the accumulation of MDA,Pro,POD was less than HK.Besides,there were lower accumulation of ABA and higher accumulation of JA in HG than in HK.There was a synergistic response mechanism of ABA and JA to drought and a high recovery ability of rehydration in HG.2.Taking pear genome as reference genome,we found 1 885 and 1 667 differentially expressed genes(DEGs)in HG and HK,which were enriched in 21 and 24 metabolic pathways(KEGG Pathways),respectively,by transcriptome analysis.Among them,both the two pear cultivars were enriched in 12 Pathways including the metabolism of abscisicacid(ABA)and jasmonate(JA).However,only DEGs of HG were enriched in the pathways of the metabolic of gibberellin(GA)and salicylate(SA).In addition,743DEGswere specifically expressed in HG These genes were annotated as transcriptional factors,kinases,glucose metabolism related genes,unsaturated fatty acid related genes,hormone and signal transduction related genes,aquaporins,stomatal closing associated actin binding proteins,calcium binding protein CML,calcium-dependent protein kinases,calcium transporters,potassium channels and potassium transporters,etc.The qRT-PCR analys is of 23 randomlyselected genes showed close concordance with RNA-Seq.3.The key enzyme gene of ABA biosynthesis,PbpNCED,in ’Huangguan’ pear was cloned.The relative expression level of PbpNCED was verified,which was consistent with the level of endogenous ABA in leaves.It was found that PbpNCED should be NCED3 by the biological information analysis.4.The results of transgenic and the wild type of Arabidopsis thaliana plants were treated under different conditions of water stress showed that the PpPP2C gene from’Whangkeumbae’ pear was successfully tranfered into the plant of Arabidopsis thaliana.The expression of PpPP2C in transgenic plants was significantly higher than that in wild type,and its expression was also consistent with the content of ABA under different treatments of water stress.The drought resistance of transgenic plants was stronger than that of wild type.