College of Forestry, Jiangxi Agricultural University/Jiangxi Provincial Key Laboratory of Silviculture, Nanchang, Jiangxi, 330045, PR China.
College of Agronomy, Jiangxi Agricultural University/Kiwifruit institute of Jiangxi Agricultural University, Nanchang, Jiangxi, 330045, PR China.
BMC Genomics. 2021 Jan 6;22(1):13. doi: 10.1186/s12864-020-07311-5.
Actinidia eriantha is a precious material to study the metabolism and regulation of ascorbic acid (AsA) because of its high AsA content. Although the pathway of AsA biosynthesis in kiwifruit has been identified, the mechanism of AsA metabolism and regulation is still unclear. The purpose of this experiment is to reveal the AsA metabolic characteristics of A. eriantha 'Ganmi 6' from the molecular level, and lay a theoretical foundation for the research on the genetic improvement of kiwifruit quality.
We found that AsA reached the accumulation peak at S7 (110 DAF) during the process of fruit growth and development. The activity of GalDH, GalLDH, MDHAR and DHAR in fruit was similar to AsA accumulation trend, and both of them were significantly positively correlated with AsA content. It was speculated that GalDH and GalLDH were key enzymes in AsA biosynthesis, while MDHAR and DHAR were key enzymes in AsA regeneration cycle, which together regulated AsA accumulation in fruit. Also, we identified 98,656 unigenes with an average length of 932 bp from the transcriptome libraries using RNA-seq technology after data assembly. There were 50,184 (50.87%) unigenes annotations in four databases. Two thousand nine hundred forty-nine unigenes were enriched into the biosynthesis pathway of secondary metabolites, among which 133 unigenes involved in the AsA and aldehyde metabolism pathways, and 23 candidate genes related to AsA biosynthesis, cycling and degradation were screened out.
Considering gene expression levels and changes of physiological traits and related enzyme activity, we concluded that the accumulation of AsA depends mainly on the L-galactose pathway, and the D-galacturonic acid pathway and AsA recycling pathway as the secondary pathways, which co-maintain the high AsA content in fruit of A. eriantha.
由于富含抗坏血酸（AsA），中华猕猴桃是研究 AsA 代谢和调控的宝贵材料。尽管猕猴桃中 AsA 生物合成途径已被鉴定，但 AsA 代谢和调控机制仍不清楚。本试验旨在从分子水平揭示中华猕猴桃‘甘美 6 号’果实 AsA 的代谢特征，为猕猴桃品质遗传改良研究奠定理论基础。
在果实生长发育过程中，AsA 于 S7（110 DAF）时达到积累高峰。果实中 GalDH、GalLDH、MDHAR 和 DHAR 的活性与 AsA 积累趋势相似，且均与 AsA 含量呈极显著正相关。推测 GalDH 和 GalLDH 是 AsA 生物合成的关键酶，而 MDHAR 和 DHAR 是 AsA 再生循环的关键酶，共同调节果实中 AsA 的积累。利用 RNA-seq 技术对组装后的转录组文库进行测序，共获得 98656 条 Unigenes，平均长度为 932bp。在 4 个数据库中有 50184 条（50.87%）Unigenes得到注释。2949 条 Unigenes富集到次生代谢物生物合成途径中，其中 133 条 Unigenes涉及 AsA 和醛代谢途径，筛选出与 AsA 生物合成、循环和降解相关的 23 个候选基因。
综合基因表达水平、生理特性变化及相关酶活性分析，认为 AsA 的积累主要依赖 L-半乳糖途径，D-半乳糖酸途径和 AsA 循环途径为次要途径，共同维持中华猕猴桃果实中高含量的 AsA。
