Comprehensive Analysis Of Storage Quality And Performance Of 8 Citrus Varieties In Hunan Province And Functional Verification Of CsbHLH085

In the fruit industry of Hunan Province,citrus planting area accounts for72.8%～74.3%.In 2018,citrus planting area of Hunan reached 384,300 hm²,with a total output of 5.285,700 tons,both ranking second in China.The annual output value of Hunan citrus is about 19.49 billion yuan.It is the main source of farmers’income in mountainous and hilly areas,as well as one of the pillar industries for poverty alleviation and prosperity.However,due to the concentration of fruitmaturity,and the lack of comprehensive evaluation of storage quality and performance of specific citrus varieties,the best delivery and sales period of various varieties are missed,leading to prominent problems such as quality decline and decay loss.Moreover,it is difficult for fruit farmers and grass-roots agricultural departments to develop citrus varieties according to local conditions,and there is a widespread phenomenon of blindly following the trend of planting.Based on this,eight citrus varieties which are popular in Hunan province in recent years:ZMPG、CX、CJ、JQSTJ、JXL、JXY、JH and JX,were selected as materials in this study.The changes of fruit quality index,the differences of storage performance between different varieties and the correlation between quality index and storage performance were analyzed.The results showed that acidity is one of the important index which affecting the storage quality and performance in different citrus fruits.The changes of TA content was significantly negatively correlated with incidence rate and weight loss during storage.Therefore,we further focused on the transcription factor CsbHLH085,which maybe participated in citrate metabolism process according to our previous study.regulates the acid metabolism of citrus fruit flavor and quality,was further used as the research object to transform the and subcellular localization analysis,overexpress of this gene in Micro-Tom tomato and interfere of this gene in BTC embryogenic callus were carried out,to preliminarily explore the function of CsbHLH085 on citric acid metabolism.Specific researches are as follows:1.Monitoring the dynamic changes of fruit quality of each variety under room and low temperature conditions.The results showed that the difference in TA content of different varieties was greater than that of TSS.The content of TA decreased gradually,while the content of TSS changed little during the whole storage process.Among them,the TA content of CX fluctuated least during the whole storage process,and its fruit flavor quality maintained the longest time.VC is one of the important nutritional quality indexes of citrus fruits,and its content fluctuates slightly during storage.Before storage,the content of VC in JX and ZM was higher than other vavieties.The juice yield reflects the slagging property of the fruit.Before storage,the juice yield of JQ-STJ was the highest,but decreased gradually at the later storage stage.The juice yield of ZM was slightly increased at the later stage.In terms of room temperature and low temperature,low temperature can maintain TA content better in fruits to some extent.At the later stage of storage,fruit juice yield was better maintained in low temperature,but with no significant effect on TSS and VC.2.To clarify the differences in fruit storage performance between different varieties under room and low temperature conditions.The changes of respiration intensity,weight loss and incidence rate of fruits during storage were analyzed.During the storage period,the respiration intensity of fruits generally followed the law of decreasing-rising-decreasing fluctuation,and the respiration intensity of CX in the tight-skin mandarin fruits was low and the fluctuation range was small.Respiratory intensity of tight-skin mandarin varieties before storage has little difference,mostly about 170.00-200.00 nmol kg^-1 s^-1.The weight loss increased gradually with the prolonging of storage time.the thicker of the fruit pericarp,the lower of wegith loss of loose-skin citrus varieties.Among them,the weight loss of CX was the lowest,while the weight loss of JX and JXY were lower,which indicated that these three varieties had better water retention ability.The incidence rate of fruit increased gradually during storage,and CX was the lowest（4.00±0.00%at 160 days of storage）,indicating that CX has the best storage performance.In terms of room and low temperature,low temperature environment was more conducive to fruit water retention,but some varieties were prone to chilling injury under low temperature.3.By comprehensive comparison of the differences in storage quality and performance of various varieties,loose-skin mandarin including ZM and CX,and tight-skin mandarin including JX and JHhad better storage quality and performance.ZM is early maturity,thin skin and flat round fruit type,were more suitable for low temperature storage.CX had the best storage performance among the selected varieties,and could be stored for 120 days without incidence,which stagger the marketing time of most citrus.It was more suitable for low temperature storage.JX has the characteristics of low acid,rich content of VC,soft and juicy,good slag melting.JH is a red-skinned sweet orange with good fruit appearance and commercial property.JX and JH are more suitable for storage at room temperature.Chilling injury is easily caused by low temperature storage.The results can provide the corresponding data support for the development of Hunan citrus industry.4.Functional analysis of CsbHLH085 gene.Subcellular localization analysis showed that CsbHLH085 was localized in the nucleus,indicating that CsbHLH085 was functional in the nucleus.At the same time,T₁ of transgenic tomato lines with overexpression of CsbHLH085 gene and transgenic calli of BTC with interference expression of CsbHLH085were obtained,which laid a solid foundation for further clarifying the mechanism of CsbHLH085 regulating citric acid in citrus fruits.After overexpression of CsbHLH085,transgenic tomatoes showed a variety of phenotypes,such as fewer seeds,larger fruits and sharper fruit type.These phenotypes suggested that CsbHLH085 may also be involved in fruit growth and development.The results of this study may have important theoretical and practical significance for regulating the level of citric acid and improving the storage quality and performance of postharvest citrus fruits by artificially regulating the expression of CsbHLH085.