Postharvest thickening of solid endosperm (SE, coconut meat) is a distinct physiological phenomenon in coconut (Cocos nucifera L.) that affects fruit quality and seed germination, yet the underlying mechanism remains largely unknown. Here, by integrating physiological and biochemical analyses, we revealed that this thickening is associated with net accumulation of cellulose and hemicellulose (HEM, predominantly galactomannan). Transcriptome profiling identified two candidate genes involved in galactomannan metabolism: CnAGAL2 encoding an α‑galactosidase and CnMAN6 encoding an endo‑β‑mannanase. Both genes were transcriptionally downregulated during storage, in parallel with a progressive decline in total α‑galactosidase and β‑mannanase activities. Functional validation via recombinant protein expression and transient overexpression in tobacco leaves demonstrated that CnAGAL2 possesses strong α‑galactosidase activity, whereas CnMAN6 showed no detectable β‑mannanase activity. During postharvest storage, reduced CnAGAL2 expression suppressed HEM degradation; meanwhile, the upregulation of cell wall biosynthetic genes further contributed to the net accumulation of cellulose and HEM, leading to SE thickening. Phylogenetic analysis indicated that CnAGAL2 belongs to the GH27 family, and subcellular localization confirmed that it is targeted to the cell periphery. Promoter analysis revealed enrichment of abscisic acid (ABA)‑responsive elements, and a dual-luciferase assay showed that exogenous ABA significantly repressed the CnAGAL2 promoter. These findings provide a molecular basis for postharvest endosperm thickening in coconut and offer insights into HEM metabolism in recalcitrant seeds.

Rapid postharvest softening is a major challenge for the kiwiberry (Actinidia arguta) industry, as it leads to significant declines in appearance, texture, flavor, and overall quality. To reduce postharvest losses and extend shelf life, various preservation techniques have been developed. This study investigated the role of hydrogen sulfide (H2S), an important gaseous signaling molecule, in delaying fruit ripening and softening. Compared to the control, H2S-treated fruits exhibited delayed color transition, higher firmness, lower total soluble solids content, and enhanced antioxidant capacity (as evidenced by significantly increased vitamin C content). Moreover, H2S treatment delayed the degradation of cell wall components (e.g. hemicellulose and pectin), thereby maintaining cell wall structural integrity. Transcriptomic and RT-qPCR analyses revealed that H2S significantly down-regulated the expression of key cell wall degradation-related genes, including AaPG1/2, AaExp1, AaPLL19, and Aaβ-Gal12. Dual-luciferase assays further identified the H2S-responsive transcription factors AaERFB3 and AaERFA4 as transcriptional activator and repressor of AaPG1 and Aaβ-Gal12, respectively. These findings reveal that H2S delays kiwiberry postharvest softening by modulating a transcriptional network involved in cell wall remodeling, providing a theoretical basis for developing improved kiwiberry preservation technologies.

It is well known that high temperatures can lead to a decrease in anthocyanin accumulation in plant organs, but there is insufficient understanding of the internal physiological factors that cause this reduction in anthocyanin accumulation. Apart from the inhibition of synthesis by high temperature, it is not clear how the branch pathways, degradation or transport of anthocyanin change dynamically with temperature increase. Taking red-fleshed kiwifruit as the material, we employed UPLC-MS/MS to investigate the levels of intermediate metabolites in the anthocyanin biosynthesis pathway and potential degradation products. The findings indicated that as the temperature rises, the upstream and downstream branch pathways of the anthocyanin synthesis pathway are adjusted accordingly. Lignin metabolism is enhanced, while the downstream anthocyanin and adjacent branch pathways jointly decrease, but the degradation of anthocyanin accelerated, concurrently with a significant decrease in anthocyanin accumulation. Additionally, the content of a representative degradation product, protocatechuic acid, significantly increased. Kinetic analysis demonstrated that as temperature rose (25-40 °C), the degradation rate constant of anthocyanins increased with the half-life decreased, and the critical temperature range for anthocyanin degradation was between 35 and 40 °C. It is confirmed that under high-temperature conditions, the flow of metabolites in the phenylpropanoid pathway of red-fleshed kiwifruit has undergone readjustment. The inhibition of synthesis and the concurrent degradation jointly contribute to the actual accumulation level of anthocyanins. Through RNA-Seq and enzyme activity experiments, we also identified two genes/enzymes that were promoted by high-temperature stimulation, laccase-12-like (Achn037101) and glucan endo-1,3-β-glucosidase (Achn008121). This study reveals the metabolic kinetics of anthocyanin metabolism in red-fleshed kiwifruit in vivo and offers a deeper understanding of anthocyanin degradation in response to high temperature.

The typical feature of red-fleshed Actinidia chinensis is the radical redness of the locules in the inner pericarp. However, in commercial orchards, we observed that kiwifruit on vines exhibiting leaf chlorosis symptoms also showed an extension of reddish flesh to the outer pericarp. The mechanisms linking anthocyanin accumulation in the outer pericarp of kiwifruit with leaf chlorosis remain poorly understood. Through establishment of the field and callus treatment experiments under iron deficiency, we analyzed element contents, fruit quality and differentially expressed genes, and confirmed that iron deficiency contributes to both the anthocyanin accumulation in the outer pericarp and the chlorosis symptoms in the leaves and fruit. Additionally, we found that genes involved in anthocyanin biosynthesis, as well as MYB75, were significantly activated, with MYB75 playing a key role in activating many of these genes. Two DELLA proteins of GA pathway were significantly induced, while LBD37like, a repressor of anthocyanin pathway, was inhibited by iron deficiency. A lot of iron transporters and storage proteins related to iron deficiency responses were identified in the over-reddened fruit. These discoveries enhance our understanding of anthocyanin regulation under iron deprivation and provide insights into how fruit responds to iron deficiency.

Actinidia arguta , the most widely distributed Actinidia species and the second cultivated species in the genus, can be distinguished from the currently cultivated Actinidia chinensis on the basis of its small and smooth fruit, rapid softening, and excellent cold tolerance. Adaptive evolution of tetraploid Actinidia species and the genetic basis of their important agronomic traits are still unclear. Here, we generated a chromosome -scale genome assembly of an autotetraploid male A. arguta accession. The genome assembly was 2.77 Gb in length with a contig N50 of 9.97 Mb and was anchored onto 116 pseudo -chromosomes. Resequencing and clustering of 101 geographically representative accessions showed that they could be divided into two geographic groups, Southern and Northern, which first diverged 12.9 million years ago. A. arguta underwent two prominent expansions and one demographic bottleneck from the midPleistocene climate transition to the late Pleistocene. Population genomics studies using paleoclimate data enabled us to discern the evolution of the species' adaptation to different historical environments. Three genes ( AaCEL1 , AaPME1 , and AaDOF1 ) related to flesh softening were identified by multi-omics analysis, and their ability to accelerate flesh softening was verified through transient expression assays. A set of genes that characteristically regulate sexual dimorphism located on the sex chromosome (Chr3) or autosomal chromosomes showed biased expression during stamen or carpel development. This chromosome -level assembly of the autotetraploid A. arguta genome and the genes related to important agronomic traits will facilitate future functional genomics research and improvement of A. arguta .

Rapid softening is one of the major concerns for the postharvest storage of kiwiberry (Actinidia arguta), which leds to quality deterioration and reduced commercial value. Understanding the mechanisms of kiwiberry ripening and softening at the molecular level becomes urgent as it could help to create kiwiberry varieties with favorable storage properties. This study analyzed the postharvest ripening process of kiwiberry and revealed that solubilization of pectin and depolymerization of hemicellulose mainly contributed to fruit softening. Based on the RNA-seq data and weighted gene co-expression network analysis (WGCNA), four cell wall degradation-related genes AaPG1, AaXTH28 and AaPME1/2 were revealed. Moreover, a bHLH transcription factor AaBIM1, which functioned as a transcriptional repressor of cell wall degradation-related genes was identified via dual-luciferase assay and yeast one-hybrid, and its expression profile showed a downward trend during postharvest ripening. Transient overexpression of AaBIM1 in kiwiberry core tissue delayed fruit softening and decreased the expression of downstream structural genes. These findings supported the critical role of AaBIM1 in regulating cell wall metabolism and provided insights into understanding kiwiberry softening for further improvement by breeding.

The fruit of Actinidia arguta are currently receiving much attention owing to their various colors in green or purple and fully edible smooth skin with unique shapes, taste appeal and rich nutritional value. A. arguta is now, after A. chinensis var. chinensis and A. chinensis var. deliciosa, the third most widely planted member of the Actinidia genus in commercial orchards. In order to improve our understanding of A. arguta and to plan future use of the germplasm for breeding elite cultivars, 189 accessions (including 14 cultivars) collected were analyzed with 200 simple sequence repeats (SSR) to explore their molecular diversity and population structure, and to identify elite alleles. The results showed all these markers used were polymorphic and generated 2496 allele loci with a polymorphism information content (PIC) value of 0.658. Through population structure analysis, the accessions have been divided into four subpopulations (K = 4), each subpopulation corresponding well with the distance-based clustering. Eleven traits were associated using MLM (mixed linear model) with markers. Marker trait association analysis identified 43 significant associations involving the 35 SSRs for the 11 traits, including some important and interesting traits in breeding such as gender and fruit quality like flesh color. Through transient expression, LR71 discovered in this study is a marker significantly associated with fruit flesh color, belongs to a gene encoding an MYB transcription factor that regulates the accumulation of anthocyanins, and causes red pigmentation. This study revealed the extent of genetic diversity and the population structure of A. arguta germplasm collected. The trait-marker pairs obtained from association mapping have potential value in molecular marker-assisted breeding, and genomics studies with gene mapping. The relationships among the natural populations touched and the origin of the cultivars mainly used are discussed, all of these help us to further understand and analyze the natural evolution of A. arguta.

The R2R3 MYB genes associated with the flavonoid/anthocyanidin pathway feature two repeats, and represent the most abundant classes of MYB genes in plants; however, the physiological role and regulatory function of most R2R3 MYBs remain poorly understood in kiwifruit (Actinidia). Here, genome-wide analysis identified 155 R2R3-MYBs in the ‘Red 5′ version of the Actinidia chinensis genome. Out of 36 anthocyanin-related AccR2R3-MYBs, AcMYB10 was the most highly expressed in inner pericarp of red-fleshed kiwifruit. The expression of AcMYB10 was highly correlated with anthocyanin accumulation in natural pigmentation during fruit ripening and light-/temperature-induced pigmentation in the callus. AcMYB10 is localized in the nuclei and has transcriptional activation activity. Overexpression of AcMYB10 elevates anthocyanin accumulation in transgenic A. chinensis. In comparison, A. chinensis fruit infiltrated with virus-induced gene silencing showed delayed red coloration, lower anthocyanin content, and lower expression of AcMYB10. The transient expression experiment in Nicotiana tabacum leaves and Actinidia arguta fruit indicated the interaction of AcMYB10 with AcbHLH42 might strongly activate anthocyanin biosynthesis by activating the transcription of AcLDOX and AcF3GT. In conclusion, this study provides novel molecular information about R2R3-MYBs in kiwifruit, advances our understanding of light- and temperature-induced anthocyanin accumulation, and demonstrates the important function of AcMYB10 in the biosynthesis of anthocyanin in kiwifruit.

A population of interspecific'Jiangshanjiao'(Actinidia chinensis Planch × A.eriantha Benth) and male A.chinensis Planch hybrids was used in this study.Sex ratio and flowering traits were investigated in the spring of 2012,2013,and 2016,respectively.The sex ratio of female to male progeny was lower than 1 ∶ 1,which means there are more male than female plants in the hybrid population.The basic petal color of the progeny was red,but a subtle segregation of color distribution,color depth,and red color types were observed in the population.Clustering analysis using extracted parameters with CMYK mode showed four subclusters,among which two groups of hybrids were consistent with scarlet and violet petal phenotypes,respectively.The early flowering season,flowering duration,flower diameter,flower number,and petal number per flower were found to have wide variations,and changed with investigation year.The average time span between the first and the last early flowering season of the hybrids was 14 d.Average proportion of the hybrids in the early flowering season reached a maximum of 25.5％ in the population.Flowering duration of the population in 2016 was the longest,with 47.4％ of hybrids blooming for 10-13 d,but was the shortest in 2013,with 55.2％ of hybrids blooming for 3-5 d.A few progenies had larger flowers and more petals per flower or more flowers per inflorescence.There were 21 combination types of petal-flower-inflorescence number in the hybrid population.

Actinidia arguta is a species native to East Asia, and its genetic diversity is largely unknown. Here, the genetic diversity of five natural A. arguta populations distributed from northeast to southwest China was evaluated with 15 simple sequence repeat (SSR) markers. The observed heterozygosity and polymorphism information content of populations from Da-Ba Mountains and Mei County in the Qin-Ling Mountains were higher than those of populations from the Chang-Bai Mountains. Analysis of molecular variance revealed 16.62% SSR variation among and 83.38% variation within populations. An unweighted pair group method with arithmetic mean clustering analysis showed clustering of the two populations from the Qin-Ling Mountains and clustering of the populations from the Da-Ba and Chang-Bai Mountains. Most wild A. arguta accessions were clustered according to the populations. These results imply that wild A. arguta resources in the Qin-Ling and Da-Ba Mountains represent a potential germplasm pool, which broadens the genetic basis of the kiwifruit germplasm for breeding. (C) 2015 Elsevier B.V. All rights reserved.

In plants, the role of anthocyanins trafficking in response to high temperature has been rarely studied, and therefore poorly understood. Red-fleshed kiwifruit has stimulated the world kiwifruit industry owing to its appealing color. However, fruit in warmer climates have been found to have poor flesh coloration, and the factors responsible for this response remain elusive. Partial correlation and regression analysis confirmed that accumulative temperatures above 25 °C (T25) was one of the dominant factors inhibiting anthocyanin accumulation in red-fleshed Actinidia chinensis, 'Hongyang'. Expression of structural genes, AcMRP and AcMYB1 in inner pericarp sampled from the two high altitudes (low temperature area), was notably higher than the low altitude (high temperature area) during fruit coloration. AcMYB1 and structural genes coordinate expression supported the MYB-bHLH (basic helix-loop-helix)-WD40 regulatory complex mediated downregulation of anthocyanin biosynthesis induced by high temperatures in kiwifruit. Moreover, cytological observations using the light and transmission electronic microscopy showed that there were a series of anthocyanic vacuolar inclusion (AVI)-like structures involved in their vacuolization process and dissolution of the pigmented bodies inside cells of fruit inner pericarp. Anthocyanin transport was inhibited by high temperature via retardation of vacuolization or reduction in AIV-like structure formation. Our findings strongly suggested that complex multimechanisms influenced the effects of high temperature on red-fleshed kiwifruit coloration.

Ploidy levels of a natural population of A. arguta from east of Daba Mountain located in a region of Shaanxi province were determined by flow cytometric analysis. Decaploids of A. arguta were the first time found in nature. The frequencies of tetraploid, hexaploid, octaploid and decaploid in the population were 36%, 11%, 33% and 20% respectively. The haploid size of A. arguta was estimated to be 776.4+/-94.82 Mb. Fruits of the female plants are purple or red color with a range of color intensity. The typical fruit shapes of those individuals vary from round, ovoid, oblong, ellipsoidal to spindle-shaped. Fruits of female plants with higher ploidy levels had smaller diameter of cross section and higher LID ratio (length/width). Contents of sugars and organic acids in fruits of the population varied largely, and D-21 was found to have extremely high accumulation of sugars and organic acids. Present data evidenced natural distribution of decaploid and the co-existence of multi-ploidy of the purple A. arguta in the east of Daba Mountain. (C) 2013 Elsevier B.V. All rights reserved.

为进一步研究野生软枣猕猴桃种质资源的遗传多样性,以软枣猕猴桃基因组DNA为模板,优化了SSR反应体系并确定了反应条件,筛选出了多态性较高的标记.从来自中华猕猴桃基因组的65对SSR引物初步筛选出15对有较好扩增带型、增稳定性好的引物,其中较好多态性的引物有12对.用筛选的引物进一步对四川天全二郎山的野生软枣猕猴桃群体进行了SSR分析,在15个个体中共检测出了141个等位基因,平均每个位点检测到9.4个等位基因,平均PIC值为0.745.

Although the biosynthetic pathways for anthocyanins and their regulation have been well studied,the cytology of anthocyanin accumulation is still less understood.Here,we used light and electron microscopy to investigate the anatomical features in pigmented inner pericarp of 'Hongyang',the mainly cultivated red kiwifruit in China,and to describe the cytological morphology of anthocyanoplasts.The results showed anthocyanoplasts and pigmented cells were formed in specific tissues.It was firstly observed that there are two forms of anthocyanoplasts,one is vesicle-like pigment bodies,and the other is the smaller intensely pigmented granule.Morphology,degradation and vacuolarization of anthocyanoplasts carriers(or anthocyanic vacuolar inclusions carriers) were also observed.Vesicle-like pigment bodies appeared in the small cells of vascular traces and its adjacent cells(VTs) in inner pericarp of 'Hongyang' at 30 days after flowering(DAF).In addition,at 68 DAF,smaller intensely pigmented granules were found in the bigger septum-originated parenchymatous cells(SEP).Anthocyanoplasts were kept in VTs at 117 DAF.Under electron microscopy,plenty of anthocyanoplasts carriers were observed in the bigger parenchymatous cells.Anthocyanoplasts in the carriers were showed to have multiple forms that reflected the coloration of the parenchymatous cells between each of two septums.Some were still keeping round,some were crescent-shaped,but others seemed to change to irregular.In general,those anthocyanoplasts became smaller and more irregular,and finally leaded to vacuolarization of the carriers to different extents.Our results described the positions of anthocyanoplasts formation and their cytological features.It was suggested that the coloration of 'Hongyang' inner pericarp was attributable to anthocyanin release after the anthocyanoplasts shift from VTs to SEP.

To elucidate the function of MYB in Actinidia chinesis 'Hongyang' pigmentation,a novel MYB gene(AcMYB) was isolated from that cultivar by reverse transcription-polymerase chain reaction(RT-PCR) and rapid amplification of cDNA ends(RACE).The full-length cDNA of AcMYB is 962 bp with an open reading frame(ORF) of 666 nucleotides encoding a protein of 221 amino acids with two typical MYB DNA binding domains at its N-terminal.The result of Blast X showed that AcMYB had high similarity with MYB transcription factors in Petunia hybrida Vilm.,Vitis spp.,Solanum lycopersicum L.,Antirrhinum majus L.and sequences from other plant species related to the elevation of anthocyanin pigmentation.Real-time PCR analysis indicated that the expression of MYB was positively correlated with the main anthocyanin concentration in Actinidia chinesis 'Hongyang' and both of them maintained high levels at the stage of pigmentation,suggesting that AcMYB may play an important role in regulating anthocyanin biosynthesis.

Based on the highly conserved sequences of other plants,counterpart sequences of CHS (chalcone synthase,CHS)and LDOX(leucoanthocyanidin dioxygenase,LDOX)of Actinida chinesis,'Hongyang'were obtained using the special primers.Full-length cDNAs encoding CHS and LDOX were cloned respectively from fruit of'Hongyang'by RACE(rapid amplification of cDNA ends).The AcCHS was 1 501 bp in length,encoding 389 amino acids.AcLDOX was 1 381 bp in length and encoded 355 amino acids.Amino acids sequence of AcCHS exhibited over 95% homology with CHS of Abelmoschus manihot,Camellia japonica and Gossypium hirsutum.It also shared 94% and 93% homology with Vitis vinifera and Malus × domestica respectively.AcLDOX showed 94% and 93% identity with Vitis amurensis and Vitis vinifera respectively at amino acids level.The expression of AcCHS and AcLDOX in the inner pericarp of three kiwifruit cultivars with red,green and yellow color was analyzed by Real-time PCR.AcCHS expressed highly in flesh of'Hongyang'at 65 DAF(days after flower).Expression of the gene in yellow-fleshed'Jinnong'decreased permanently after flowering.Expression of AcLDOX increased during the early developmental stage in'Hongyang',but dropped quickly after 65 DAF.Interestingly,expression of AcLDOX raised markedly in the late developmental stages of green-fleshed'Jinkui',which was the highest among three cultivars.AcLDOX in'Jinnong'also deregulated after flowering.

Big fruit size and nice red pigmentation combined with good flavor should be the major target for red-fleshed kiwifruit ( Actinidia spp.) breeding programs. Genetic diversity and plant characteristics were evaluated on a set of kiwifruit accessions with predominantly red flesh to identify the superior individuals for further breeding or study of commercial application. The leading phenotypic characters varied widely among the accessions. Accession R reached average fruit weight ≈100 g, whereas it ranged from 43.15 to 84.71 g for the other accessions. Fruits of L and Q were flatter in shape than the others. The core volume accounted for fruit proportions ranging from 2.33% to 11.42%. ‘Chuhong’, ‘Honghua’, and K exhibited a round fruit apex, whereas most others showed a depressed apex. R, L, and Q had the highest a* values in the inner pericarp and also the most appealing visual coloration. Results revealed significantly higher soluble solid content (SSC), total sugar, and sugar/acid ratio in Q, R, and L. The 12 pairs of simple sequence repeat (SSR) markers were successfully used to characterize the genetic variability and confirm true-to-type identity for four accessions. However, the limited number of markers had no ability to discriminate among the other 11 accessions. Based on additional 28 SSRs, six of the indistinguishable accessions were confirmed to be genetically different, and three seemed to belong to the same clone vine. The results demonstrated that application of SSR data could improve the efficiency of identifying red-fleshed kiwifruit germplasm.

Twelve genes related to anthocyanin synthesis were isolated from the red flesh of the kiwifruit cultivar, Actinidia chinensis var. chinensis 'Hongyang', by cDNA and SSH library sequencing and homologue cloning. These genes include partial-or full-length structural genes, chalcone synthase (CHS), chalcone isomerase (CHI), flavanone 3-hydroxylase (F3H), dihydroflavonol 4-reductase (DFR), leucoanthocyanin deoxygenase (LDOX), UDP-glucose: flavonoid 3-O-glucosyltransferase (UFGT) and UDPG, regulatory genes as myeloblast (MYB) and tryptophan-aspartate (WD) proteins, and transporting proteins such as multidrug resistance-associated proteins(MRP)-like ABC transporters. The isolated AcF3H ORF was 1101 bp in length, which encoded a 366 amino-acid peptide. AcF3H expression level was high before coloration, and then decreased at the early stage. Real-time PCR showed that AcDFR1 expression was extremely high in a green-fleshed cultivar, A. chinensis var. deliciosa 'Jinkui', at anthesis, and remained very high during later development, but was lower in the yellow-fleshed cultivar, A. chinensis var. chinensis 'Jinnong', and the red-fleshed 'Hongyang'. Expression of AcDFR2 was very low at all stages of 'Jinkui', but higher in 'Jinnong' and 'Hongyang'. Nevertheless, transcription levels of AcDFR1 and AcDFR2 increased with fruit coloration of the yellow/red-fleshed cultivars, especially in the later stages of development.