Role Of HY5 In The Carotenoid Synthesis Of Tomato Fruits

Tomato(Solanum lycopersicum)is one of the most popular and widely consumed vegetable in the world,and it has attracted much attention because of its high content of antioxidants such as carotenoids.With research of different variety and improvement of cultivation techniques,consumers have higher requirements for the nutritional quality and health functions of tomato.Therefore,exploiting the internal mechanism that promotes the production of carotenoids in tomato fruits to improve varieties and cultivation methods has positive significance for improving tomato fruit quality.HY5 is one of the important regulators of plant photomorphogenesis proceed.In recent years,research on HY5 regulating carotenoid synthesis and accumulation has gradually increased under different environments,but related research in tomato has not been reported.This paper explores the role of light in tomato fruit maturation and carotenoid anabolic metabolism.Using different mutant materials of the HY5 gene as research objects,we then study the function of HY5 in tomato carotenoid anabolic metabolism.The mobility of HY5 between leaves and fruits and its effect on carotenoid synthesis in fruits were preliminary investigated.The main results obtained are as follows:1.Light is not necessary for tomato fruit to mature,but the lack of light restricts the accumulation of carotenoids in the fruit and reduces the content of glucose,fructose and ascorbic acid.Chlorophyll in tomato fruits is rapidly degraded in the dark,but tomato can still reach the breaker stage of ripeness after 38 days of flowering.After bagging,the gene expressions of DXS,PSY1,PDS,ZDS,CrtISO in fruits were downregulated,and contents of lycopene,β-carotene and lutein were reduced.Fruit quality was also affected by dark.The contents of glucose,fructose and ascorbic acid in the fruits were significantly reduced,while the contents of sucrose,malic acid and citric acid were less affected.2.HY5 can combine the promoters of lycopene synthesis genes PSY1 and PDS to promote carotenoid synthesis in fruits.The expression levels of PSY1,PDS,ZDS,CrtISO in HY5 overexpression materials were higher than those of wild-type and hy5-RNAi mutants at all stages of fruit maturation.Contents of lycopene and β-carotene had same trend: HY5-OE>wild type>hy5-RNAi.EMSA and dual-luciferase expression assays proved that HY5 can bind to the Z-box of PSY1 promoter and C/G-box on the PDS promoter to induce gene expression.In terms of fruit quality,HY5 may promote the transfer of sucrose from source to sink by regulating sucrose transport-related proteins,affecting the conversion of sucrose to fructose and glucose in the fruit,but the specific mechanism remains to be answered.3.HY5 protein in leaves can be transferred to fruits,which has a positive effect on carotenoid anabolic metabolism and fruit quality.Using grafting,we obtained a combination material with hy5-RNAi as the scion and HY5-OE as the rootstock.The upper leaves of the scion were removed to ensure that the rootstock leaves were the main photosynthesis site.The results showed that the contents of lycopene and β-carotene in the fruit of hy5/HY5-OE grafted seedlings were higher than that of hy5/ hy5,and PSY1,PDS,ZDS,CrtISO were also upregulated.The content of HY5 protein in fruits at mature green stage of hy5/HY5-OE increased.We speculate that HY5 in leaves can directly participate in the transcriptional regulation of PSY1 and PDS in fruits,and can also activate the transcription of itself in fruits,increasing protein accumulation,but the specific mechanism has not been fully elucidated.In summary,HY5 participates in tomato fruit maturation under the activation of light.HY5 can directly activate lycopene synthesis genes PSY1 and PDS through binding their promoters to promote carotenoid synthesis.HY5 also promotes sugar transport and transformation,improving tomato fruit quality.At the same time,HY5 in the leaves can be transferred to the fruit to activate itself and lycopene synthesis gene expression,which has a positive effect on the carotenoid accumulation and fruit quality of tomato fruits.