Evaluation of Blue Honeysuckle Berries (Lonicera caerulea L.) Dried at Different Temperatures: Basic Quality, Sensory Attributes, Bioactive Compounds, and In Vitro Antioxidant Activity.

This study aims to comprehensively investigate the effects of hot-air dehydration on the quality of blue honeysuckle berries (Lonicera caerulea L.). The results demonstrated that drying with hot air at 40-65 °C for 7-72 h resulted in blue honeysuckle berries with a moisture content of 0.21-1.10 g H2O/g dry weight. Generally, low to medium temperatures (40-55 °C) showed a better effect on the quality than high temperatures (60-65 °C). Specifically, drying at 40 °C exclusively resulted in better retention of cuticular wax, the best sensory appearance, and the highest total phenolic content. Drying at 45 °C and 50 °C resulted in the highest antioxidant capacity and the optimal sensory flavor. Drying at 55 °C led to the highest soluble solid/acid ratio, ascorbic acid concentration, total flavonoid, and total anthocyanin. The work introduces an innovative raw berry product and provides a comprehensive practical and theoretical framework for convective dehydration of blue honeysuckle berries.

Molecular regulation of oil gland development and biosynthesis of essential oils in Citrus spp.

Secretory structures in terrestrial plants serve as reservoirs for a variety of secondary metabolites. Among these, the secretory cavity of the Rutaceae family is notable for containing essential oils with a wide range of applications. However, the molecular basis underlying secretory cavity development is unknown. Here, we reveal a molecular framework for Citrus oil gland formation. Using genetic mapping and genome editing, we demonstrated that this process requires LATE MERISTEM IDENTITY1 (LMI1), a key regulator of leaf serration. A conserved GCC box element of the LMI1 promoter recruits DORNROSCHEN-like (DRNL) for transcriptional activation. This DRNL-LMI1 cascade triggers MYC5 activation, facilitating the development of oil glands and the biosynthesis of essential oils. Our findings spotlight cis-regulatory divergence within leaf shape genes, propelling novel functional tissue formation.

AcMYB10 Involved in Anthocyanin Regulation of 'Hongyang' Kiwifruit Induced via Fruit Bagging and High-Postharvest-Temperature Treatments.

Light and temperature are key factors influencing the accumulation of anthocyanin in fruit crops. To assess the effects of fruit bagging during development and high post-ripening temperature on 'Hongyang' kiwifruit, we compared the pigmentation phenotypes and expression levels of anthocyanin-related genes between bagged and unbagged treatments, and between 25 °C and 37 °C postharvest storage temperatures. Both the bagging and 25 °C treatments showed better pigmentation phenotypes with higher anthocyanin concentrations. The results of the qRT-PCR analysis revealed that the gene expression levels of LDOX (leucoanthocyanidin dioxygenase), F3GT (UDP-flavonoid 3-O-glycosyltransferase ), AcMYB10, and AcbHLH42 were strongly correlated and upregulated by both the bagging treatment and 25 °C storage. The results of bimolecular fluorescence complementation and luciferase complementation imaging assays indicated an interaction between AcMYB10 and AcbHLH42 in plant cells, whereas the results of a yeast one-hybrid assay further demonstrated that AcMYB10 activated the promoters of AcLODX and AcF3GT. These results strongly suggest that enhanced anthocyanin synthesis is caused by the promoted expression of AcLODX and AcF3GT, regulated by the complex formed by AcMYB10-AcbHLH42.

Transposable elements cause the loss of self-incompatibility in citrus.

Self-incompatibility (SI) is a widespread prezygotic mechanism for flowering plants to avoid inbreeding depression and promote genetic diversity. Citrus has an S-RNase-based SI system, which was frequently lost during evolution. We previously identified a single nucleotide mutation in Sm-RNase, which is responsible for the loss of SI in mandarin and its hybrids. However, little is known about other mechanisms responsible for conversion of SI to self-compatibility (SC) and we identify a completely different mechanism widely utilized by citrus. Here, we found a 786-bp miniature inverted-repeat transposable element (MITE) insertion in the promoter region of the FhiS2-RNase in Fortunella hindsii Swingle (a model plant for citrus gene function), which does not contain the Sm-RNase allele but are still SC. We demonstrate that this MITE plays a pivotal role in the loss of SI in citrus, providing evidence that this MITE insertion prevents expression of the S-RNase; moreover, transgenic experiments show that deletion of this 786-bp MITE insertion recovers the expression of FhiS2-RNase and restores SI. This study identifies the first evidence for a role for MITEs at the S-locus affecting the SI phenotype. A family-wide survey of the S-locus revealed that MITE insertions occur frequently adjacent to S-RNase alleles in different citrus genera, but only certain MITEs appear to be responsible for the loss of SI. Our study provides evidence that insertion of MITEs into a promoter region can alter a breeding strategy and suggests that this phenomenon may be broadly responsible for SC in species with the S-RNase system.

Evaluation of the Harvest Dates for Three Major Cultivars of Blue Honeysuckle (Lonicera caerulea L.) in China.

Blue honeysuckle (Lonicera caerulea L.) is an emerging fruit crop; however, determining its proper harvest time in commercial cultivation remains challenging due to its rapid fruit development characteristics. In this study, we investigated 17 agronomic traits of three blue honeysuckle cultivars harvested on 5 successive dates within their respective harvest windows. 'Lanjingling', 'Wulan', and 'Berel' showed solid-acid ratios (SS:TA) ranging from 10.00 to 16.01, 8.13 to 10.23, and 5.77 to 7.11, respectively; anthocyanin contents ranged from 233.85 to 276.83 mg/100 g, 236.38 to 312.23 mg/100 g, and 235.71 to 334.98 mg/100 g, respectively; vitamin C contents ranged from 88.43 to 99.68 mg/100 g, 108.13 to 191.23 mg/100 g, and 89.71 to 120.40 mg/100 g, respectively; phenolic contents ranged from 25.22 to 37.59 mg/g, 25.40 to 36.52 mg/g, and 37.66 to 50.00 mg/g, respectively. The results revealed the SS:TA value consistently increased with delayed harvesting and were significantly negatively correlated with fruit firmness, total acidity, shelf life, and respiration intensity, suggesting it is an ideal maturity indicator for blue honeysuckle berries. The factor analysis suggests that the suitable harvest date for 'Lanjingling' could be either 47 days after flowering (DAF) with an SS:TA value of approximately 10.0, characterized by high firmness, extended shelf life, and elevated levels of anthocyanins and phenolics; or 67 DAF (SS:TA ≈ 16.0), characterized by high vitamin C content and sweetness, and larger size and weight. For 'Wulan', it suggests the suitable harvest date is either 54 DAF (SS:TA ≈ 9.0), yielding fruit with high levels of anthocyanins and vitamin C; or 62 DAF (SS:TA > 10.0), yielding fruit with high sweetness and large size and weight. For 'Berel', it is suggested to be either 52 DAF (SS:TA ≈ 6.5), resulting in fruit with high levels of anthocyanins and vitamin C; or 62 DAF (SS:TA > 7.0), resulting in balanced levels of the fruit quality traits.

Complete chloroplast genome assembly and phylogenetic analysis of blackcurrant (Ribes nigrum), red and white currant (Ribes rubrum), and gooseberry (Ribes uva-crispa) provide new insights into the phylogeny of Grossulariaceae.

Background: Blackcurrant (Ribes nigrum), red currant (R. rubrum), white currant (R. rubrum), and gooseberry (R. uva-crispa) belong to Grossulariaceae and are popular small-berry crops worldwide. The lack of genomic data has severely limited their systematic classification and molecular breeding. Methods: The complete chloroplast (cp) genomes of these four taxa were assembled for the first time using MGI-DNBSEQ reads, and their genome structures, repeat elements and protein-coding genes were annotated. By genomic comparison of the present four and previous released five Ribes cp genomes, the genomic variations were identified. By phylogenetic analysis based on maximum-likelihood and Bayesian methods, the phylogeny of Grossulariaceae and the infrageneric relationships of the Ribes were revealed. Results: The four cp genomes have lengths ranging from 157,450 to 157,802 bp and 131 shared genes. A total of 3,322 SNPs and 485 Indels were identified from the nine released Ribes cp genomes. Red currant and white currant have 100% identical cp genomes partially supporting the hypothesis that white currant (R. rubrum) is a fruit color variant of red currant (R. rubrum). The most polymorphic genic and intergenic region is ycf1 and trnT-psbD, respectively. The phylogenetic analysis demonstrated the monophyly of Grossulariaceae in Saxifragales and the paraphyletic relationship between Saxifragaceae and Grossulariaceae. Notably, the Grossularia subgenus is well nested within the Ribes subgenus and shows a paraphyletic relationship with the co-ancestor of Calobotrya and Coreosma sections, which challenges the dichotomous subclassification of the Ribes genus based on morphology (subgenus Ribes and subgenus Grossularia). These data, results, and insights lay a foundation for the phylogenetic research and breeding of Ribes species.

Complete chloroplast genome and phylogenetic analysis of Lonicera caerulea var. edulis (Caprifoliaceae).

Lonicera caerulea var. edulis, known as "blue honeysuckle" or "Haskap," is a deciduous shrub that belongs to the Caprifoliaceae family. Characterized by the high cold hardiness and high quality of fruit, it has become a novel cash crop in cold regions worldwide. The lack of available chloroplast (cp) genome information limits studies of its molecular breeding and phylogeny. Here, the complete cp genome of Lonicera caerulea var. edulis was assembled and characterized for the first time. It was 155,142 bp in length with 38.43% of GC content, including 23,841 bp inverted repeat regions (IRs), an 88,737 bp large single-copy region (LSC), and an 18,723 bp small single-copy region (SSC). A total of 132 genes, including 85 protein-coding genes, 8 rRNA genes, and 39 tRNA genes were annotated. Phylogenetic analysis indicated that L. caerulea var. edulis was closely related to L. tangutica. These data and results provide a valuable resource for the development of breeding tools and genetic diversity studies for L. caerulea.

Structural variation and parallel evolution of apomixis in citrus during domestication and diversification.

Apomixis, or asexual seed formation, is prevalent in Citrinae via a mechanism termed nucellar or adventitious embryony. Here, multiple embryos of a maternal genotype form directly from nucellar cells in the ovule and can outcompete the developing zygotic embryo as they utilize the sexually derived endosperm for growth. Whilst nucellar embryony enables the propagation of clonal plants of maternal genetic constitution, it is also a barrier to effective breeding through hybridization. To address the genetics and evolution of apomixis in Citrinae, a chromosome-level genome of the Hongkong kumquat (Fortunella hindsii) was assembled following a genome-wide variation map including structural variants (SVs) based on 234 Citrinae accessions. This map revealed that hybrid citrus cultivars shelter genome-wide deleterious mutations and SVs into heterozygous states free from recessive selection, which may explain the capability of nucellar embryony in most cultivars during Citrinae diversification. Analyses revealed that parallel evolution may explain the repeated origin of apomixis in different genera of Citrinae. Within Fortunella, we found that apomixis of some varieties originated via introgression. In apomictic Fortunella, the locus associated with apomixis contains the FhRWP gene, encoding an RWP-RK domain-containing protein previously shown to be required for nucellar embryogenesis in Citrus. We found the heterozygous SV in the FhRWP and CitRWP promoters from apomictic Citrus and Fortunella, due to either two or three miniature inverted transposon element (MITE) insertions. A transcription factor, FhARID, encoding an AT-rich interaction domain-containing protein binds to the MITEs in the promoter of apomictic varieties, which facilitates induction of nucellar embryogenesis. This study provides evolutionary genomic and molecular insights into apomixis in Citrinae and has potential ramifications for citrus breeding.

Genome sequencing and CRISPR/Cas9 gene editing of an early flowering Mini-Citrus (Fortunella hindsii).

Hongkong kumquat (Fortunella hindsii) is a wild citrus species characterized by dwarf plant height and early flowering. Here, we identified the monoembryonic F. hindsii (designated as 'Mini-Citrus') for the first time and constructed its selfing lines. This germplasm constitutes an ideal model for the genetic and functional genomics studies of citrus, which have been severely hindered by the long juvenility and inherent apomixes of citrus. F. hindsii showed a very short juvenile period (~8 months) and stable monoembryonic phenotype under cultivation. We report the first de novo assembled 373.6 Mb genome sequences (Contig-N50 2.2 Mb and Scaffold-N50 5.2 Mb) for F. hindsii. In total, 32 257 protein-coding genes were annotated, 96.9% of which had homologues in other eight Citrinae species. The phylogenomic analysis revealed a close relationship of F. hindsii with cultivated citrus varieties, especially with mandarin. Furthermore, the CRISPR/Cas9 system was demonstrated to be an efficient strategy to generate target mutagenesis on F. hindsii. The modifications of target genes in the CRISPR-modified F. hindsii were predominantly 1-bp insertions or small deletions. This genetic transformation system based on F. hindsii could shorten the whole process from explant to T1 mutant to about 15 months. Overall, due to its short juvenility, monoembryony, close genetic background to cultivated citrus and applicability of CRISPR, F. hindsii shows unprecedented potentials to be used as a model species for citrus research.