The Investigation Into The Mechanisms Of Postharvest Lignification Regulation In Kiwifruit Induced By Low Temperature

Kiwifruit is climacteric,and its market time is concentrated,so it is difficult to store at room temperature for a long time.Cold storage effectively inhibits fruit softening and extends the postharvest life of kiwifruits.However,fruit that stored in an unsuitable low-temperature environment for a long period are likely to develop chilling injury and produces lignification which will have a severe impact on its industrial value.It is vital to understand the regulation mechanisms of postharvest kiwifruit chilling injury and lignification.In this study,’Hongyang’ kiwifruit with cold sensitivity was used as the main experimental material.By means oftransmission electron microscopy(TEM),RNA-Seq,q RT-PCR,dual luciferase assay and transient overexpression,chilling injury(CI)and lignification-related genes were screened,and their regulatory mechanism was analyzed.It provides a new basis mechanism for kiwifruit postharvest chilling.The main results were listed below:1.Compared with ’Huayou’ and ’Xuxiang’ kiwifruit,’Hongyang’ kiwifruit showed more obvious lignification under cold stress.Therefore,’Hongyang’ kiwifruit was selected as the main research object.In chilling-temperature,the activities of cinnamate 4-hydroxylase(C4H)and cinnamic acid hydroxylation 4-coumarate-Co A(4CL)enzymes were continuously activated in the whole storage period,while the activities of phenylalanine ammonia-lyase(PAL)enzymes were only activated in the early storage period.2.Based on transcriptome sequencing data,key enzyme genes and candidate regulatory factors for lignin synthesis were screened.Ac C4H1 from C4 H family and Ac4CL3/4/5/7from 4CL family were higher expression than others and were up-regulated by cold stress,which was similar to the lignin accumulation pattern at cold stress temperature and non-cold stress temperature.Application of melatonin to postharvest kiwifruit effectively alleviated CI symptom,alleviated of CI-induced lignification coincided with the coordinated suppression of 4CL and C4 H activities.These results support that the application of melatonin to kiwifruit was an effective postharvest technique to alleviate CI.Meanwhile,four MYB transcriptional activators(AcMYB5/12/13/14)which responded to cold stress and whose expression patterns were consistent with lignin accumulation patterns were screened.3.The promoter sequences of Ac4CL3,Ac4CL4,Ac4CL5,Ac4CL7 and Ac C4H1 were analyzed,and it was found that these contained several AC-binding elements and SMRE-binding elements.The results of dual luciferase assay and promoter site-directed mutagenesis indicated that AcMYB12/AcMYB13 could activate its activity by binding different SMRE binding elements on Ac4CL3.MYB5/14 could bind AC elements in Ac C4H1 promoter and induce its activity Overexpression of AcMYB5/12/13/14 could up-regulate the expression of downstream genes of lignin synthesis,and the lignin content increased slightly but did not show a significant level.To sum up,the mechanism of postharvest chilling injury in kiwifruit fruit was analyzed under cold stress and non-cold stress treatments.Four MYB transcription factors that regulate postharvest chilling injury lignification of kiwifruit were screened by transcriptome sequencing,and their regulatory mechanisms were analyzed.All these results further revealed the molecular mechanism of kiwifruit lignification under cold stress.These results provided new insights into the molecular mechanism of kiwifruit postharvest lignification under cold stress.