Dynamic Changes of Phenolic Compounds and Their Associated Gene Expression Profiles Occurring during Fruit Development and Ripening of the Donghong Kiwifruit

Transcriptome and biochemical analyses reveal phenolic compounds-mediated flavor differences in loquat (Eriobotrya japonica Lindl.) cultivars Chunhua No.1 and Dawuxing

The novel loquat cultivar 'Chunhua No.1' (CH1) is a promising commercial cultivar. However, CH1 has texture characteristics different from those of common loquat, and its formation mechanism remains unclear. Here, we first identified the phenolic compounds of CH1 and its parent ('Dawuxing', DWX) and the effect on texture formation. The special presence of stone cells explained the flavor differences in CH1. Chlorogenic acid, neochlorogenic acid, and coniferyl alcohol were the main phenolic compounds in loquat, and the high content of coniferyl alcohol was a potential factor for the rough texture of CH1. Transcriptome reveals that phenylpropanoid metabolism was activated during CH1 fruit texture formation. Kyoto Encyclopedia of Genes and Genomes (KEGG) identified 51 structural genes involved in phenylpropanoid biosynthesis, and Weighted Gene Co-expression Network Analysis (WGCNA) identified four structural genes and 88 transcription factors. These findings provide new insights into the phenolic metabolism and flavor formation of loquat fruit.

Dynamic Changes of Phenolic Composition, Antioxidant Capacity, and Gene Expression in 'Snow White' Loquat (Eriobotrya japonica Lindl.) Fruit throughout Development and Ripening

The newly released 'Snow White' (SW), a white-fleshed loquat (Eriobotrya japonica Lindl.) cultivar, holds promise for commercial production. However, the specifics of the phenolic composition in white-fleshed loquats, along with the antioxidant substances and their regulatory mechanisms, are not yet fully understood. In this study, we examined the dynamic changes in the phenolic compounds, enzyme activities, antioxidant capacity, and gene expression patterns of SW during the key stages of fruit development and ripening. A total of 18 phenolic compounds were identified in SW, with chlorogenic acid, neochlorogenic acid, and coniferyl alcohol being the most predominant. SW demonstrated a stronger antioxidant capacity in the early stages of development, largely due to total phenolics and flavonoids. Neochlorogenic acid may be the most significant antioxidant contributor in loquat. A decline in enzyme activities corresponded with fruit softening. Different genes within a multigene family played distinct roles in the synthesis of phenolics. C4H1, 4CL2, 4CL9, HCT, CCoAOMT5, F5H, COMT1, CAD6, and POD42 were implicated in the regulation of neochlorogenic acid synthesis and accumulation. Consequently, these findings enhance our understanding of phenolic metabolism and offer fresh perspectives on the development of germplasm resources for white-fleshed loquats.

Methylation of AcGST1 Is Associated with Anthocyanin Accumulation in the Kiwifruit Outer Pericarp

Most red-fleshed kiwifruit cultivars, such as Hongyang, only accumulate anthocyanins in the inner pericarp; the trait of full red flesh becomes the goal pursued by breeders. In this study, we identified a mutant "H-16" showing a red color in both the inner and outer pericarps, and the underlying mechanism was explored. Through transcriptome analysis, a key differentially expressed gene AcGST1 was screened out, which was positively correlated with anthocyanin accumulation in the outer pericarp. The result of McrBC-PCR and bisulfite sequencing revealed that the SG3 region (-292 to -597 bp) of AcGST1 promoter in "H-16" had a significantly lower CHH cytosine methylation level than that in Hongyang, accompanied by low expression of methyltransferase genes (MET1 and CMT2) and high expression of demethylase genes (ROS1 and DML1). Transient calli transformation confirmed that demethylase gene DML1 can activate transcription of AcGST1 to enhance its expression. Overexpression of AcGST1 enhanced the anthocyanin accumulation in the fruit flesh and leaves of the transgenic lines. These results suggested that a decrease in the methylation level of the AcGST1 promoter may contribute to accumulation of anthocyanin in the outer pericarp of "H-16".

Genome-wide identification of the AcMADS-box family and functional validation of AcMADS32 involved in carotenoid biosynthesis in Actinidia

MADS-box is a large transcription factor family in plants and plays a crucial role in various plant developmental processes; however, it has not been systematically analyzed in kiwifruit. In the present study, 74 AcMADS genes were identified in the Red5 kiwifruit genome, including 17 type-I and 57 type-II members according to the conserved domains. The AcMADS genes were randomly distributed across 25 chromosomes and were predicted to be mostly located in the nucleus. A total of 33 fragmental duplications were detected in the AcMADS genes, which might be the main force driving the family expansion. Many hormone-associated cis-acting elements were detected in the promoter region. Expression profile analysis showed that AcMADS members had tissue specificity and different responses to dark, low temperature, drought, and salt stress. Two genes in the AG group, AcMADS32 and AcMADS48, had high expression levels during fruit development, and the role of AcMADS32 was further verified by stable overexpression in kiwifruit seedlings. The content of α-carotene and the ratio of zeaxanthin/β-carotene was increased in transgenic kiwifruit seedlings, and the expression level of AcBCH1/2 was significantly increased, suggesting that AcMADS32 plays an important role in regulating carotenoid accumulation. These results have enriched our understanding of the MADS-box gene family and laid a foundation for further research of the functions of its members during kiwifruit development.

Two haplotype-resolved, gap-free genome assemblies for Actinidia latifolia and Actinidia chinensis shed light on the regulatory mechanisms of vitamin C and sucrose metabolism in kiwifruit

Kiwifruit is a recently domesticated horticultural fruit crop with substantial economic and nutritional value, especially because of the high content of vitamin C in its fruit. In this study, we de novo assembled two telomere-to-telomere kiwifruit genomes from Actinidia chinensis var. 'Donghong' (DH) and Actinidia latifolia 'Kuoye' (KY), with total lengths of 608 327 852 and 640 561 626 bp for 29 chromosomes, respectively. With a burst of structural variants involving inversion, translocations, and duplications within 8.39 million years, the metabolite content of DH and KY exhibited differences in saccharides, lignans, and vitamins. A regulatory ERF098 transcription factor family has expanded in KY and Actinidia eriantha, both of which have ultra-high vitamin C content. With each assembly phased into two complete haplotypes, we identified allelic variations between two sets of haplotypes, leading to protein sequence variations in 26 494 and 27 773 gene loci and allele-specific expression of 4687 and 12 238 homozygous gene pairs. Synchronized metabolome and transcriptome changes during DH fruit development revealed the same dynamic patterns in expression levels and metabolite contents; free fatty acids and flavonols accumulated in the early stages, but sugar substances and amino acids accumulated in the late stages. The AcSWEET9b gene that exhibits allelic dominance was further identified to positively correlate with high sucrose content in fruit. Compared with wild varieties and other Actinidia species, AcSWEET9b promoters were selected in red-flesh kiwifruits that have increased fruit sucrose content, providing a possible explanation on why red-flesh kiwifruits are sweeter. Collectively, these two gap-free kiwifruit genomes provide a valuable genetic resource for investigating domestication mechanisms and genome-based breeding of kiwifruit.

Dynamic Changes in Ascorbic Acid Content during Fruit Development and Ripening of Actinidia latifolia (an Ascorbate-Rich Fruit Crop) and the Associated Molecular Mechanisms

Actinidia latifolia is one of the very few kiwifruit genotypes with extremely high ascorbic acid (AsA) content. However, a transcriptome atlas of this species is lacking. The accumulation of AsA during fruit development and ripening and the associated molecular mechanisms are still poorly understood. Herein, dynamic changes in AsA content at six different stages of A. latifolia fruit development and ripening were determined. AsA content of A. latifolia fruit reached 1108.76 ± 35.26 mg 100 g−1 FW at full maturity. A high-quality, full-length (FL) transcriptome of A. latifolia was successfully constructed for the first time using third-generation sequencing technology. The transcriptome comprises 326,926 FL non-chimeric reads, 15,505 coding sequences, 2882 transcription factors, 18,797 simple sequence repeats, 3328 long noncoding RNAs, and 231 alternative splicing events. The genes involved in AsA biosynthesis and recycling pathways were identified and compared with those in different kiwifruit genotypes. The correlation between the AsA content and expression levels of key genes in AsA biosynthesis and recycling pathways was revealed. LncRNAs that participate in AsA-related gene expression regulation were also identified. Gene expression patterns in AsA biosynthesis and metabolism exhibited a trend similar to that of AsA accumulation. Overall, this study paves the way for genetic engineering to develop kiwifruits with super-high AsA content.

Comparative transcriptome analysis reveals variations of bioactive constituents in Lonicera japonica flowers under salt stress

Lonicera japonica flowers (LJF) is a traditional Chinese medicine packed with phenols constituents and widely used in the treatments of various diseases throughout the world. However, there is still very little known on how LJF identifies and resists salt stress. Here in, we systematically investigated the effect of salt on the phenotypic, metabolite, and transcriptomic in LJF. During long term stress (35 days), 1055 differential expression genes (DEGs) involved in the biosynthesis of secondary metabolites were screened through transcriptome analysis, among which the candidate genes and pathways involved in phenols biosynthesis were highlighted; and performed by phylogenetic tree analysis and multiple nucleotide sequence alignment. Ninety compounds were identified and their relative levels were compared between the control and stressed groups based on the LC-MS analysis, Putative biosynthesis networks of phenolic acid and flavonoid were con-structed with structural DEGs. Strikingly, the expression patterns of structural DEGs were mostly consistent with the variations of phenols under salt stress. Notably, the upregulation of UDP-glycosyl transferases under salt stress indicated post-modification of glycosyl transferases may participate in downstream flavonoids synthesis. This study reveals the relationships of the gene regulation and the phenols biosynthesis in LJF under salt stress, paving the way for the use of gene-specific expression to improve the yield of biocomponent.

Protective effect of coix seed seedling extract on 60 Co-γ radiation-induced oxidative stress in mice

Exposure to ionizing radiation (IR) can cause oxidative damage to human body, leading to various diseases and even death. In this study, the potential radioprotective effect of coix seed seedling extract (CSS-E) was studied through a model of ⁶⁰ Co-γ radiation-induced oxidative stress in mice. Overall radioprotective effect of CSS-E against radiation-induced damage was evaluated by biochemical analysis and histopathological analysis. The results showed that CSS-E could significantly reduce the IR-induced damage to the hematopoietic system. CSS-E-M (200 mg/kg BW) pretreatment could increase the activities of superoxide dismutase in serum, liver, and spleen increased by 31.68%, 45.10%, and 56.67%, respectively, and the glutathione peroxidase levels in serum, liver, and spleen of mice were improved by 19.17%, 41.97%, and 130.56%, respectively. Meanwhile, the glutathione levels of serum, liver, and spleen in CSS-E-M group were increased by 17.10%, 35.06%, and 40.71%, respectively. The contents of MDA in different tissues and serum could be reduced by CSS-E-M treatment to the normal level. Moreover, CSS-E could markedly reduce the activities of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) in radiation mice, among which CSS-E-M group showed maximum restoration with decreased AST and ALT levels by 20.13% and 32.76% as compared against IR group. In conclusion, these results indicated that CSS-E could be used as a potential natural radioprotectant against IR-induced damage.