Effects Of CaCl₂ Treatment On Physiological Characteristics,Gene Expression And Metabolites Of ’Fucuimi’ Jujube Fruit Cracking

Fucuimi is a fresh food variety with early maturity and high yield,drought resistance,storage resistance,disease resistance,high sugar content,thin skin and thick meat.It is sour,sweet and palatable,with excellent taste,and is deeply loved by consumers.However,the high rate of fruit cracking has seriously affected the fruit quality and yield.In this paper,the cracking rate,peel anatomical structure and peel cell wall metabolic enzyme activity of jujube in the key period of fruit cracking（69d-90d after full bloom）were measured by spraying exogenous CaCl₂.The transcriptome and metabolomics of jujube peel samples treated with natural,clean water and CaCl₂at 69d,81d and 90d after full bloom were analyzed to screen the genes and differential metabolites related to fruit cracking,so as to provide a theoretical basis for scientific prevention and control of fruit cracking.1.The fruit cracking rate of CaCl₂Treatment was significantly lower than that of natural and water treatment;Spraying CaCl₂significantly reduced the activities of cellulase,pectinase,SOD and pod in jujube peel.The cat enzyme activity of jujube peel treated with CaCl₂was significantly higher than that of natural and clean water treatment from 84d to 90d after flowering.After CaCl₂treatment,the cuticle of jujube peel was relatively complete,the thickness of cuticle,epidermis,inner surface cortex and the number of cells in inner epidermis increased significantly,and the cells arranged closely.2.The transcriptome of CaCl₂treated samples was sequenced by Illumina platform,and the changes of transcript level under CaCl₂treatment were analyzed by combining bioinformatics methods.With the increase of fruit cracking time,the number of differentially expressed genes under CaCl₂treatment increased first and then decreased.The number of differentially expressed genes was the largest in the middle of fruit cracking.Through GO and KEGG analysis,it was found that the pathways significantly annotated under CaCl₂treatment were mainly sugars,Phenylpropanes and lipids.The expression of POD42and IAA14 genes under CaCl₂Treatment was low 81 days after full flowering;The gene expressions of pectinate lyase PL5-2,PMEIs41,CML and GASAL in CaCl₂treatment were higher than those in natural and clean water treatment at 81 days of full flowering stage;Under CaCl₂treatmentβ-GAL3,GDSL-APG,XET1,XET2 and other genes were highly expressed in the early stage of fruit cracking,while GDSL-1 and other genes were low expressed under CaCl₂treatment;Compared with CaCl₂treatment,the expression of POD17 gene increased rapidly in high incidence period under natural and clear water treatment;Pectinesterase PE3 decreased significantly in the high incidence stage of fruit cracking under CaCl₂treatment,indicating that these 14 genes may be involved in the process of fruit cracking,and 14 genes play a key role in the regulation of fruit cracking under Catreatment.3.Using non targeted metabonomics technology,the changes of metabolites in jujube peel sam ples at different stages of jujube cracking under CaCl₂treatment were studied.The results showed that 32 different metabolites were found in the two comparison groups of natural vs CaCl₂and cle ar water vs CaCl₂,mainly sugars,amino acids,flavonoids and esters.D-Ribose,D-Arabitol,Trehal ose,Galactaric acid,Tricetin,Epicatechin,L-asparagine,2-hydroxycinnamic acid,4-hydroxycinnamic acid and m-coumaric acid were specifically expressed under CaCl₂treatment.KEGG results show ed that the differential metabolites were annotated in’Flavonoid biosynthesis’,’Aminoacyl-t RNA bio synthesis’,’Pentose phosphate pathway’,’Phenylpropanoid biosynthesis’,’Pentose and glucuronate inte rconversions’and other metabolic pathways.4.the combined analysis of transcriptome and metabolome showed that lipid metabolites and r elated genes,phenylpropane metabolites and related genes,carbohydrate metabolites and related gen es,and the interaction between differential genes and differential metabolites jointly regulated the f ruit cracking of fuzui honey jujube.Among them,POD17 and POD42 genes were significantly cor related with 4-hydroxycinnamic acid and 2-hydroxycinnamic acid.