Analysis of organic acid metabolism reveals citric acid and malic acid play major roles in determining acid quality during the development of kiwifruit (Actinidia eriantha).

BACKGROUND: Actinidia eriantha is one of the most important kiwifruit species in Actinidia. The relative high accumulation of organic acids in fruit of A. eriantha is an unfavorable factor for organoleptic quality. To identify key metabolic enzymes and genes involved in organic acids accumulation during fruit development, physiological, biochemical, and molecular experiments were conducted for the dynamic fruit samples of a new kiwifruit cultivar, A. eriantha 'Ganlv 1'. RESULTS: The contents of citric acid and malic acid increased greatly during fruit development, while quinic acid content decreased obviously. Significant positive correlations were observed between fruit titratable acidity and the contents of both citric acid and malic acid, and a significant negative correlation was found between fruit titratable acidity and the quinic acid content. The high accumulation of citric acid was found to be caused by the increased activity of citrate synthase (CS), and the decreased activities of two degradation-related enzymes, mitochondrial aconitase and nicotinamide adenine dinucleotide (NAD)-dependent isocitrate dehydrogenase. In addition, the accumulation of malic acid depended mainly on the increased synthesis catalyzed by NAD-dependent malate dehydrogenase (NAD-MDH) and phosphoenolpyruvate carboxylase. Further analysis suggested that AeCS2 and AeMDH2 played pivotal roles in controlling the activities of CS and NAD-MDH respectively. CONCLUSION: The high accumulation level of citric acid relied on both the strong synthesis ability and the weak degradation ability. The accumulation level of malic acid was mainly affected by the synthesis. The novel information would be helpful for our understanding of the formation of fruit acidity quality. © 2023 Society of Chemical Industry.

Genome-Wide Association Studies Provide Insights into the Genetic Determination of Flower and Leaf Traits of Actinidia eriantha.

Kiwifruit (Actinidia eriantha) is a dioecious vine, and the pollen of its male cultivars has a direct effect on the quality of its fruits. In this study, to facilitate molecular breeding and gene identification, we performed genome-wide association studies (GWAS) on 11 traits of flower and leaf. A total of 946,337 highly consistent SNP markers were obtained in the whole genome. Phylogenetic tree analysis and population structure analysis showed that the 143 germplasms can be divided into two groups. The linkage disequilibrium analysis showed that A. eriantha have a relatively fast attenuation rate, and that the average attenuation distance of LD was 0.1-0.3 Kb. The MLM (QK) model was determined as best for correlation analysis, and eight and three SNPs associated with flower- and leaf-related traits were identified, respectively, at 0.01 significance level. However, SNP markers associated with stamen number per flower, pollen viability, total chlorophyll content, and total flavonoid content were not identified at the 0.01 significant level, although it is worth noting that one, one, five, and two SNPs were identified to be associated with these traits at the 0.05 significant level. This study provides insights into the complex flower- and leaf-related biology, and identifies genes controlling important traits in A. eriantha through GWAS, which extends the genetic resources and basis for facilitating molecular breeding in kiwifruits.

Three metabolic pathways are responsible for the accumulation and maintenance of high AsA content in kiwifruit (Actinidia eriantha).

BACKGROUND: 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. RESULTS: 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. CONCLUSIONS: 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.

Differences of sucrose accumulation concentration and related genes expression between two sucrose accumulation types of Actinidia eriantha.

According to the investigation of wild Actinidia eriantha in Jiangxi province of China, we found that soluble solids content of fruit was lower than edible standard (14%). However, we found a high-sugar type A. eriantha line (code was 'MM24', test material) during investigative process at Nancheng county (E 116° 48', N 26° 23', 845 m). We sheared its scions to asexual reproduction in Fengxin County (rootstock was A. deliciosa 'Miliang 1' with 7 years old) and at the same time DUS (Distinctness, Uniformity and Stability) test was also carried out. There were uncontested differences between the two comparative genotypes according to the results of polyacrylamide gel electrophoresis, it can be judged as a new cultivar. In addition, there was great similarity on most important morphological and quality characteristics. While, there was difference on SSC, DM and TS between the two materials on ripen fruit, these indicators were much higher on test material than on control. The sugar degree assessment showed that the sugar degree of test material was strong and retention time was long. Further, no sucrose was found before DAF 135 d in test material and sucrose were significantly higher than in control only at DAF 165 d and DAF 175 d. The qRT-PCR results of sucrose-related genes showed that the relative expression levels of AcSPS1, AcSPS3, AcSPS5 and AcSUS5 genes were consistent with the sucrose accumulation trend, which was probably the main genes for the difference in sugar degree.

The synergic effect of BRAFV600E mutation and multifocality on central lymph node metastasis in unilateral papillary thyroid carcinoma.

The purpose of this study is to evaluate the potential synergic effect of BRAFV600E mutation and multifocality on central lymph nodes metastasis (CLNM) in the patients with unilateral papillary thyroid carcinoma (PTC). We enrolled 413 patients with unilateral PTCs who accepted prophylactic unilateral or bilateral central lymph node dissection (LND). Univariate and multivariate analyses were made to determine the association between related factors and CLNM. Then, all patients were divided into 4 groups based on their status of BRAFV600E mutation and multifocality. Relative excess risk of interaction (RERI), attributable proportion (AP) of interaction and synergy index (SI) were applied to evaluate the interactive effect of these two factors on CLNM. Results showed that BRAFV600E mutation and multifocality were independent risk factors for CLNM. A further study revealed that unilateral PTCs accompanying multifocality with BRAFV600E mutation had the highest incidence of CLNM compared with other subgroups. Besides, RERI was 4.323 (95% CI = 1.276-7.369), AP was 0.523 (95% CI = 0.364-0.682) and SI was 2.469 (95% CI = 1.607 to 3.794), indicating a significant additive interaction of BRAFV600E mutation and multifocality on CLNM. The present study has confirmed that BRAFV600E mutation and multifocality are risk factors for CLNM in unilateral PTC. Additionally, unilateral PTC patients accompanying multifocality with BRAFV600E mutation may have an increased risk of CLNM in clinically negative CLNM.