Expression Of Related Genes During Dietary Fiber Accumulation In Rosa Roxburghii Fruit

Rosa roxburghii Tratt.fruit has a high dietary fiber content,and the ratio of water-soluble dietary fiber to insoluble is moderate,therefore,it is a good natural raw material for high-quality dietary fiber;meanwhile,some components of dietary fiber may become an obstacle to the improvement of processing quality due to the high content.So far,the genes involved in the synthesis and accumulation of dietary fiber and the factors affecting its expression during the development of R.roxburghii fruit have not been studied systematically.In this study,R.roxburghii‘Guinong 5’was used as the plant material.Based on the systematic determination of the content changes of dietary fiber components during the growth and development of R.roxburghii fruit,the relevant genes involved in the synthesis and accumulation of dietary fiber components were screened from the results of previous fruit transcriptome sequencing,and their expression characteristics and correlations with the accumulation of each component were analyzed.Finally,the main results are outlined below:1.Screening and identification of genes involved in dietary fiber metabolism in R.roxburghii fruit Based on the known plant dietary fiber metabolic pathways and transcriptome data of R.roxburghii fruits,139 candidate structural gene m RNA sequences involved in the metabolism of dietary fiber components in R.roxburghii fruits were identified.By sequence alignment,33independent transcripts（genes）were confirmed to be significantly（p<0.05）correlated with the contents of the corresponding components of dietary fiber in fruits at 30,60 and 90 d after anthesis.It mainly includes:There are four cellulose synthase（Ces A）genes involved in cellulose metabolism（Ces A1/2/3/5）,and a hydrolase-cellulase（Cx）gene involved in cellulose decomposition（Cx）,and three genes（IRX,ARAD1/2）involved in hemicellulose synthesis,includingα-1,4-xylosyltransferase（IRX）and arabinosyltransferase（ARAD）.What’s more,there are 19 genes（CCR1/2/3/4,C3’H,Cco AOMT,HCT,COMT1/2,CAD,POD1/2/3/4/5/6 and 4CL1/2/3）involved in lignin synthesis,including cinnamoyl-Co A reductase（CCR）,coumaroylquinate 3′-monooxygenase（C3’H）,caffeoyl-Co AO-methyltransferase（Cco AOMT）,shikimateO-hydroxycinnamoyltransferase（HCT）,caffeic acid O-methyltransferase（COMT）,cinnamyl alcohol dehydrogenase（CAD）,peroxidase（POD）and 4-coumaroyl/Co A ligase（4CL）;There are 5 galacturonosyltransferase（GAUT）genes involved in pectin synthesis（GAUT1/2/3/4/5）and 1 pectin methylesterase（PME）gene（PME）involved in pectin decomposition.2.Validation of the changes of dietary fiber components and their relationship with gene expression during the fruit development of R.roxburghii The genes screened above were verified by q RT-PCR,and the correlation between them and the changes of corresponding component content was analyzed.The results showed that the expression levels of Ces A1/2/5,IRX,ARAD2,CCR1,POD1/6,HCT and GAUT3/4 were consistent and significantly positively correlated with the contents of cellulose,hemicellulose,lignin and pectin,but the expression levels of Cx and GAUT were negatively correlated with cellulose and pectin content,respectively.These results indicated that the above genes played a major role in regulating dietary fiber accumulation during the fruit development of R.roxburghii.3.Regulation of dietary fiber composition and related gene expression in R.roxburghii fruit by shading and exogenous calcium treatment After 15 d anthesis,the fruits of R.roxburghii were shaded by 50%and 100%with white single-layer fruit bags（the light transmittance was about 50%as measured by illuminometer）and khaki double-layer fruit bags（the light transmittance was 0 as measured by illuminometer）,respectively.Samples were collected and determined at 30,60 and 90 d after anthesis.The results showed that shading treatment promoted the accumulation of cellulose,lignin and pectin in mature fruits.And 50%shading treatment increased the content of soluble pectin by 16.39%,which can obviously improve the taste of fruit.However,100%shading treatment increased the content of lignin by 28.86%,which can decrease the fresh food quality of fruits.The q RT-PCR analysis indicated that the expression levels of Ces A1/2/3,IRX,ARAD2,GAUT3 and CAD were responded to shading obviously and showed significant correlation with the corresponding components of dietary fiber（p<0.05）.The fruit was sprayed with 2 mmol/L Ca²⁺at the 10 d after anthesis and treated every 15 d（6 times in total）.Samples were collected at 30,60 and 90 d after anthesis for analysis.Compared with control,the results showed that the contents of cellulose,lignin and soluble pectin in mature fruits increased by 16.32%,31.7%and 33.82%,respectively.The q RT-PCR results indicated that the expression levels of Ces A3/5,Cx,ARAD2,IRX,CAD,COMT2,POD6,GAUT1/2 and PME were responded to Ca²⁺and showed significant correlation with corresponding components（p<0.05）.4.Effects of SA,ABA and ETH on accumulation of dietary fiber components and expression of related genes in R.roxburghii fruit The fruit were sprayed with SA,ABA and ETH after 10 d of anthesis and treated every 15d（6 times）.The samples were collected and analyzed at 30,60 and 90 d after anthesis.The results showed that compared with CK,SA,ABA and ETH treatments decreased hemicellulose content by 59.89%,51%and 48.76%at 60 d after anthesis,respectively.At 90 d after anthesis,SA and ABA treatments increased soluble pectin content by 31.83%and 118%,and lignin content by 15.9%and 12.98%in comparison with CK,respectively.The q RT-PCR results showed that the expression levels of ARAD1,ARAD2,CCR2,CCR3,CCR4,HCT,POD2,POD4,POD5,C3’H,4CL1,GAUT3 and PME were responded to SA,ABA and ETH obviously and showed significant correlation with the corresponding components of dietary fiber.The above results showed that different growth regulators could regulate dietary fiber components by regulating the transcriptional levels of structural genes in fruits.