Analysis Of Physiological Characteristics And Differential Gene Expression Of Fruit Cracking In Pear

In recent years,there are more and more reports about the huge economic losses in production caused by pear fruit cracking.Fruit cracking is a phenomenon due to the discordant between internal growth and external environment of fruit that lead to dehiscent on fruit surface,always occurred in the fruit mature period after rainstorm.In order to solve the industrial problem,firstly,this study has conducted an investigation and statistics on pear cracking rate,then carried on the comparative analysis on the physicochemical properties of pears which have different cracking rate,finally discussed the comparisons between physicochemical properties of normal and cracking susceptible pears as well as the analysis on spectral analysis of the digital gene expression,the main research results are as follows:1.The study has conducted an investigation on fruit cracking rate of 101pear cultivars at Jiangpu horticulture pear germplasm garden of Nanjing Agricultural University,20 pear cultivars occurred cracking phenomenon in total,namely ’Shinseiki’,’Zhongli1’,’Fanshan’,’Longquanl9’,’Xinhang’,’Xueqing’,’Qingkui’,’548-135’,’Kousui’,’Xueying’,’Lvyun,,’Yaqing’,’Xuefang’,,’Mantianhong,,’Zaoguan’,’Nanyue’,’Annong 2’,’Zaomeisu’,’Hakko’ and ’Xinya’,19.80%of the total.The fruit cracking rate of’Shinseiki’ was the highest,reached 12.76%,followed by ’Zhonglil’ and’Fanshan’,fruit cracking rate were 9.63%and 9.19%respectively,’Xinya’ has the lowest cracking rate with 0.73%.The survey also found that:solar orientation was more easily to crack,early and mid early maturing cultivars were more easily to crack.2.Select the cracking susceptible cultivars ’Shinseiki’,’Zhonglil’ and the cracking resistant cultivar ’Mantianhong’ as test materials,measure the contents of mineral elements,structure of the cell wall material and activity of related cell wall enzymes in the peel and pulp respectively.Ca content in the peel of cracking susceptible cultivars was significantly lower than the cracking resistant cultivars,activities of PPO and POD of peel and pulp and activities of PG and PME of peel were significantly higher than the cracking resistant cultivars.The contents of hemi cellulose and Na2CO3 soluble pectin(SSP)were significantly lower than those of the cracking resistant cultivars.These significant differences of physiological index were the main reasons affecting the fruit cracking rate.3.Select ’Shinseiki’ with the highest cracking rate as test material,measure and compare cell wall structure material and cell wall metabolism activity of the normal and cracking fruit pericarp,and find that the content of Na2CO3 soluble pectin(SSP),EDTA soluble pectin(CSP),cellulose,hemicellulose and lignin element in cracking fruit peel were significantly lower than that in normal fruit peel,activity of PPO,POD,cellulose(CE)and pectinase(PG)was significantly higher than that in normal fruit peel.4.Through based on high-throughput sequencing of RNA-seq expression spectrum analysis technique,from the whole genome expression of significant difference in gene expression level analysis of pear fruit cracking.The results show that these differences expressed genes mainly involved in encoding a plant hormone(jasmonic acid and ethylene)signaling pathway,horny layer of wax biosynthesis,cell wall relaxation factor(Expansin,XET,β-Gal,Cellulase,Polygalacturonase,Amylase),regulation of transcription factors(WRKY gene and bHLH gene)etc.The discovery of these genes,provide clues to further reveal the molecular mechanism of pear fruit cracking occurred from the perspective of molecular biology.