Kiwifruit is commonly sensitive to waterlogging stress, and grafting onto a waterlogging-tolerant rootstock is an efficient strategy for enhancing the waterlogging tolerance of kiwifruit plants. KR5 (Actinidia valvata) is more tolerant to waterlogging than ‘Hayward’ (A. deliciosa) and is a potential resistant rootstock for kiwifruit production. Here, we focused on evaluating the performance of the waterlogging-sensitive kiwifruit scion cultivar ‘Zhongmi 2′ when grafted onto KR5 (referred to as ZM2/KR5) and Hayward (referred to as ZM2/HWD) rootstocks, respectively, under waterlogging stress. The results showed ‘Zhongmi 2′ performed much better when grafted onto KR5 than when grafted onto ‘Hayward’, exhibiting higher photosynthetic efficiency and reduced reactive oxygen species (ROS) damage. Furthermore, the roots of ZM2/KR5 plants showed greater root activity and energy supply, lower ROS damage, and more stable osmotic adjustment ability than the roots of ZM2/HWD plants under waterlogging stress. In addition, we detected the expression of six key genes involved in the kiwifruit waterlogging response mechanism, and these genes were remarkably induced in the ZM2/KR5 roots but not in the ZM2/HWD roots under waterlogging stress. Moreover, principal component analysis (PCA) further demonstrated the differences in the physiological responses of the ZM2/KR5 and ZM2/HWD plants under waterlogging stress. These results demonstrated that the KR5 rootstock can improve the waterlogging tolerance of grafted kiwi plants by regulating physiological and biochemical metabolism and molecular responses.

Kiwifruit (Actinidia chinensis) is a nutrient-dense fruit abundant in vitamin C and phenolic compounds, and it exhibits strong antioxidant capacity. However, the antioxidants in ‘Jinfeng’ kiwifruit have seldom been extracted and analyzed, and the conditions for the extraction of kiwifruit antioxidants by ultrasound-assisted extraction (UAE) have seldom been investigated. In this study, response surface methodology (RSM) was used to optimize UAE conditions to extract antioxidants from ‘Jinfeng’ kiwifruit. In addition, the antioxidant capacity, contents of total phenolics and total flavonoids, ascorbic acid, and the profiles of antioxidants were also analyzed. The results showed that the optimal UAE conditions included 68% ethanol, liquid/solid ratio at 20 mL/g, extraction time at 30 min, extraction temperature at 42 °C, and ultrasonic power at 420 W. Under these conditions, the ABTS value of kiwifruit was 70.38 ± 1.38 μM TE/g DW, which was 18.5% higher than that of the extract obtained by conventional solvent extraction. The total phenolic and flavonoid contents were 15.50 ± 0.08 mg GAE/g DW and 5.10 ± 0.09 mg CE/g DW, respectively. Moreover, 20 compounds were tentatively identified by UPLC–MS/MS, and the content of main compounds, such as procyanidin B2, neochlorogenic acid, and epicatechin, were determined by HPLC–DAD. This research revealed the profiles of antioxidant phytochemicals in ‘Jinfeng’ kiwifruit, which can be a good dietary source of natural antioxidants with potential health functions.

Pseudomonas syringae pv. actinidiae (Psa), a bacterial pathogen, is a severe threat to kiwifruit production. To elucidate the species-specific interaction between Psa and kiwifruit, transcriptomic-profiles analyses were conducted, under Psa-infected treatment and mock-inoculated control, on shoots of resistant Maohua (MH) and susceptible Hongyang (HY) kiwifruit varieties. The plant hormone-signal transduction and plant–pathogen interaction were significantly enriched in HY compared with MH. However, the starch and sucrose metabolism, antigen processing and presentation, phagosome, and galactose metabolism were significantly enriched in MH compared with HY. Interestingly, the MAP2 in the pathogen/microbe-associated molecular patterns (PAMPs)-triggered immunity (PTI) was significantly up-regulated in MH. The genes RAR1, SUGT1, and HSP90A in the effector-triggered immunity (ETI), and the NPR1 and TGA genes involved in the salicylic acid signaling pathway as regulatory roles of ETI, were significantly up-regulated in HY. Other important genes, such as the CCRs involved in phenylpropanoid biosynthesis, were highly expressed in MH, but some genes in the Ca²⁺ internal flow or involved in the reactive oxygen metabolism were obviously expressed in HY. These results suggested that the PTI and cell walls involved in defense mechanisms were significant in MH against Psa infection, while the ETI was notable in HY against Psa infection. This study will help to understand kiwifruit bacterial canker disease and provide important theoretical support in kiwifruit breeding.

Background: Pectate lyase (PL, EC 4.2.2.2), as an endo-acting depolymerizing enzyme, cleaves α-1,4-glycosidic linkages in esterified pectin and involves a broad range of cell wall modifications. However, the knowledge concerning the genome-wide analysis of the PL gene family in Fragaria vesca has not been thoroughly elucidated. Results: In this study, sixteen PLs members in F. vesca were identified based on a genome-wide investigation. Substantial divergences existed among FvePLs in gene duplication, cis-acting elements, and tissue expression patterns. Four clusters were classified according to phylogenetic analysis. FvePL6, 8 and 13 in cluster II significantly contributed to the significant expansions during evolution by comparing orthologous PL genes from Malus domestica, Solanum lycopersicum, Arabidopsis thaliana, and Fragaria×ananassa. The cis-acting elements implicated in the abscisic acid signaling pathway were abundant in the regions of FvePLs promoters. The RNA-seq data and in situ hybridization revealed that FvePL1, 4, and 7 exhibited maximum expression in fruits at twenty days after pollination, whereas FvePL8 and FvePL13 were preferentially and prominently expressed in mature anthers and pollens. Additionally, the co-expression networks displayed that FvePLs had tight correlations with transcription factors and genes implicated in plant development, abiotic/biotic stresses, ions/Ca²⁺, and hormones, suggesting the potential roles of FvePLs during strawberry development. Besides, histological observations suggested that FvePL1, 4 and 7 enhanced cell division and expansion of the cortex, thus negatively influencing fruit firmness. Finally, FvePL1-RNAi reduced leaf size, altered petal architectures, disrupted normal pollen development, and rendered partial male sterility. Conclusion: These results provide valuable information for characterizing the evolution, expansion, expression patterns and functional analysis, which help to understand the molecular mechanisms of the FvePLs in the development of strawberries.

Rosa roxburghii Tratt, the most popular fruit that blooms in the southwest of China, has high antioxidant properties and is rich in different flavonoids. However, the regulatory network and critical genes that regulate the flavonoid biosynthesis of R. roxburghii are still unknown. In this study, HPLC analysis revealed that total flavonoids, anthocyanins, and catechin were enriched in mature fruits, flowers, and leaves, respectively. Differentially expressed genes (DEGs) between five organs of R. roxburghii involved in flavonoid metabolism were obtained by transcriptome sequencing. A total of 1130 DEGs were identified, including 166 flavonoid pathway biosynthesis genes, 622 transcription factors (TFs), 301 transporters, and 221 cytochrome P450 proteins. A weighted gene co-expression network analysis (WGCNA) of the DEGs was conducted to construct co-expression networks. Regarding enzymes in the biosynthesis of flavonoids, cytochrome P450 CYP749A22 and CYP72A219 were highlighted in the regulation of total flavonoids of mature fruits. Anthocyanin 3-O-glucosyltransferase and F3′H were the top two critical enzymes for anthocyanin accumulation in flowers. By contrast, caffeic acid 3-O-methyltransferase, 4-coumarate-CoA ligase, and shikimate O-hydroxycinnamoyltransferase were essential for catechin accumulation in leaves. Additionally, we analyzed the eigengene network of the “black” module, which had high correlations with total flavonoids (r = 0.9, p = 5 × 10⁻⁶). There were 26 eigengenes in the “black” module, consisting of 6 flavonoid biosynthesis, 14 TFs, and 6 transporters. Among them, the transcription factors RrWRKY45 (DN142829_c1_g5), RrTCP20 (DN146443_c1_g1), and RrERF118 (DN141507_c3_g2) were screened as the hub genes, which significantly correlated with total flavonoids in R. roxburghii. The present biochemical and transcriptomic data provide insights into functional genomics for breeding R. roxburghii with flavonoid accumulation.

The Gram-negative bacterial species Pectobacterium actinidiae causes summer canker in kiwifruit plants. However, little is known about its virulence factors and mechanisms of genetic adaptation. We aimed to identify the key determinants that control the virulence of P. actinidiae in kiwifruit by genomic and functional analyses. Analysis of four P. actinidiae isolates indicated low genetic variability with an average of 98.7% genome-level sequence similarity and 82% shared protein-coding gene content. Phylogenetic analysis, based on both bulk single nucleotide polymorphisms (SNPs) and single-copy genes, revealed that P. actinidiae strains cluster into a single clade, which is closely related to the clades of P. odoriferum (species with a completely different host range). Through comparison between these two clades of strains, 746 unique core orthologs/genes were clustered in the clades of P. actinidiae, especially key virulence determinants involved in the biosynthesis of secretion systems (type III, IV, and VI), iron, flagellar structure, and the quorum-sensing system. Our results provide insights into the pathogenomics underlying the genetic diversification and evolution of pathogenicity in P. actinidiae species.