A high-quality apple genome assembly reveals the association of a retrotransposon and red fruit colour

The role of mobile DNA elements in the dynamics of plant genome plasticity

Plants host a range of DNA elements capable of self-replication. These molecules, usually associated with the activity of transposable elements or viruses, are found integrated in the genome or in the form of extrachromosomal DNA. The activity of these elements can impact genome plasticity by a variety of mechanisms, including the generation of structural variants, the shuffling of regulatory or coding DNA sequences across the genome, and DNA endoduplication. This plasticity can dynamically alter gene expression and genome stability, ultimately affecting plant development or the response to environmental changes. While the activation of these elements is often considered deleterious to the genome, their role in creating variation is important in adaptation and evolution. Moreover, the mechanisms by which mobile DNA proliferates have been exploited for plant engineering, or contributed to understand how desirable traits can be generated in crops. In this review, we discuss the origins and the roles of mobile DNA element activity on genome plasticity and plant biology, as well as their potential function and current application in plant biotechnology.

Genome-wide patterns of local adaptation associated with transposable elements in Tetrastigma hemsleyanum (Vitaceae)

The mobility of transposable elements (TEs) partly drives genome evolution, potentially leading to either adaptive or deleterious effects. However, it remains far from clear whether and how TEs contribute to adaptation to changing environments, especially in plants. We analyzed whole-genome sequencing data from 29 ecologically diverse Tetrastigma hemsleyanum populations to infer the species' demographic history and its impact on TE polymorphisms. Integrated selective sweep and genome-environment association (GEA) approaches were employed to examine the contribution of TEs to environmental adaptation. The ancestor of T. hemsleyanum diverged during the late Miocene/Pliocene, forming two lineages that further split into four sublineages. These (sub)lineages underwent periodic population declines and recoveries during the late-Pleistocene climatic oscillations, with most polymorphic TEs transposing during the last glacial period. A small fraction of these TEs (0.033-0.40%) showed signatures of positive selection, while a broader subset (0.081-0.76%) correlated significantly with climatic variables. Notably, these selected or climate-linked TE polymorphisms were preferentially retained in gene-poor regions and frequently linked to genes involved in organ development and stress/defense response. Our findings demonstrate that TEs played a key regulatory and adaptive role in T. hemsleyanum's response to environmental change, underscoring their importance in better understanding the genomic mechanisms underlying adaptation.

Integrative Analyses of Metabolome and Transcriptome Reveal Scion-Stock Asymmetry Reduction and Shift of Sugar Metabolism During Graft Junction Formation in Malus Domestica ('Hanfu') Homograft

Grafting is widely used as a breeding method to enhance productivity and resilience. However, the mechanisms of graft healing remain poorly understood. In this study, we performed Malus domestica ('Hanfu') homograft and observed morphological and anatomical changes during the healing process in the graft junction within 40 days after grafting (DAG). The results showed that the healing process was divided into two phases: 0-20 days (callus proliferation phase) and 20-40 days (vascular bundle reconnection phase). During the early stage (20 DAG), gene expression exhibited asymmetry between the scion and rootstock, whereas synchronization occurred in the late stage (40 DAG). Transcriptomic and metabolomic analyses of the scion and rootstock during these two critical phases identified that differentially expressed genes (DEGs) were enriched in "Carbon fixation by Calvin cycle" and "photosynthesis-related pathways", while differentially expressed metabolites (DEMs) were clustered in "Galactose metabolism", implying a critical role of carbohydrates in grafting. Genes encoding enzymes involved in sugar biosynthesis, such as amylase (MdAMY), invertase (MdINV), galactinol synthase (MdGS), raffinose synthase (MdRS), and stachyose synthase (MdSS), were generally more highly expressed during Phase I than Phase II. In contrast, genes encoding enzymes related to sugar consumption, such as fructose kinases (MdSUS), cellulose synthases (MdCESA), and galacturonosyltransferase (MdGAUT), showed weak expression in Phase I but were strongly activated in Phase II. Glucose, sucrose, galactose, and melibiose levels increased significantly at 20 DAG compared with 0 DAG and subsequently decreased by 40 DAG. Exogenous application of 0.5% sucrose, raffinose, or melibiose significantly enhanced vascular bundle reconnection rates at 7 DAG compared with the control group (p < 0.01), confirming the pivotal role of sugar metabolism in graft healing.

DNA Methylation and Alternative Splicing Safeguard Genome and Transcriptome After a Retrotransposition Burst in Arabidopsis thaliana

Transposable elements (TEs) are major drivers of plant genome plasticity, but the immediate molecular consequences of new TE insertions remain poorly understood. In this study, we generated a wild-type Arabidopsis thaliana population with novel insertions of ONSEN retrotransposon to investigate early epigenomic and transcriptomic changes using whole-genome and cDNA nanopore sequencing. We found that novel ONSEN insertions were distributed non-randomly, with a strong preference for genic regions, particularly in chromatin enriched for H2A.Z, H3K27me3, and H3K4me2. Most full-length ONSEN insertions within genes were rapidly recognized and spliced out as new introns (intronization), thereby mitigating potential deleterious effects on transcript isoforms. In some cases, ONSEN insertions provided alternative transcription start or termination sites, generating novel transcript isoforms. Genome-wide methylation analysis revealed that new ONSEN copies were efficiently and precisely targeted by DNA methylation. Independently on the location of the original ONSEN element, the euchromatic and heterochromatic insertions display distinct methylation signatures, reflecting the action of different epigenetic pathways. In conclusion, our results demonstrate that DNA methylation and alternative splicing are effective control mechanisms safeguarding the plant genome and transcriptome integrity after retrotransposition burst.

Apple varieties, diseases, and distinguishing between fresh and rotten through deep learning approaches

Apples are one of the most productive fruits in the world, in addition to their nutritional and health advantages for humans. Even with the continuous development of AI in agriculture in general and apples in particular, automated systems continue to encounter challenges identifying rotten fruit and variations within the same apple category, as well as similarity in type, color, and shape of different fruit varieties. These issues, in addition to apple diseases, substantially impact the economy, productivity, and marketing quality. In this paper, we first provide a novel comprehensive collection named Apple Fruit Varieties Collection (AFVC) with 29,750 images through 85 classes. Second, we distinguish fresh and rotten apples with Apple Fruit Quality Categorization (AFQC), which has 2,320 photos. Third, an Apple Diseases Extensive Collection (ADEC), comprised of 2,976 images with seven classes, was offered. Fourth, following the state of the art, we develop an Optimized Apple Orchard Model (OAOM) with a new loss function named measured focal cross-entropy (MFCE), which assists in improving the proposed model's efficiency. The proposed OAOM gives the highest performance for apple varieties identification with AFVC; accuracy was 93.85%. For the apples rotten recognition with AFQC, accuracy was 98.28%. For the identification of the diseases via ADEC, it was 99.66%. OAOM works with high efficiency and outperforms the baselines. The suggested technique boosts apple system automation with numerous duties and outstanding effectiveness. This research benefits the growth of apple's robotic vision, development policies, automatic sorting systems, and decision-making enhancement.

Haplotype-resolved genome assembly provides new insights into the genomic origin of purple colour in Prunus mume

Prunus mume, an important ornamental woody plant in the Rosaceae family, contains many interspecific hybridizations. Purple colour is a breeding trait of aesthetic value for P. mume, but little is known about the origin and genetic architecture of this trait. Here we address these issues by producing a haplotype-resolved genome from an interspecific hybrid cultivar of P. mume (M) and P. cerasifera 'Pissardii' (C), named P. mume 'Meiren', followed by a detailed molecular characterization. The final length of the diploid genome is 499.47 Mb, with 250.66 Mb of haplotype M (HM) and 248.79 Mb of haplotype C (HC). Approximately 95.42% (476.61 Mb) of the phased assembly is further anchored to 16 homologous chromosomes. Based on the genomic variation, we identify a 1.8 Mb large-fragmented inversion (INV) on chromosome 1b of HC, which co-segregates with purple colour traits of 'Meiren' inherited from its purple C parent 'Pissardii'. We find that a MYB transcription factor, PmmMYB10.5b, resides at the distal breakpoint of the INV, which displays consistent allele-specific expression (ASE). By directly binding to the promoter of anthocyanin synthetic alleles, PmmMYB10.5b serves as a co-activator to promote anthocyanin accumulation in 'Meiren' organs. Notably, the INV identified in 'Meiren' is generated from 'Pissardii' rather than P. cerasifera, which alters the promoter sequence of PmmMYB10.5b, activates its expression and results in the purple colour trait. Results from this study shed light on the evolutionary origin of purple colour in 'Meiren' and could potentially provide guidance on the genetic improvement of colour traits in ornamental woody plants.

Centrophilic Retrotransposons of Plant Genomes

The centromeres of eukaryotic chromosomes are required to load CENH3/CENP-A variant nucleosomes and the kinetochore complex, which connects to spindle microtubules during cell division. Despite their conserved function, plant centromeres show rapid sequence evolution within and between species and a range of monocentric, holocentric, and polymetacentric architectures, which vary in kinetochore numbers and spacing. Plant centromeres are commonly composed of tandem satellite repeat arrays, which are invaded by specific families of centrophilic retrotransposons, whereas in some species the entire centromere is composed of such retrotransposons. We review the diversity of plant centrophilic retrotransposons and their mechanisms of integration, together with how epigenetic information and small RNAs control their proliferation. We discuss models for rapid centromere sequence evolution and speculate on the roles that centrophilic retrotransposons may play in centromere dynamics. We focus on plants but draw comparisons with animal and fungal centromeric transposons to highlight conserved and divergent themes across the eukaryotes.

Pan-genome analysis reveals the evolution and diversity of Malus

Malus Mill., a genus of temperate perennial trees with great agricultural and ecological value, has diversified through hybridization, polyploidy and environmental adaptation. Limited genomic resources for wild Malus species have hindered the understanding of their evolutionary history and genetic diversity. We sequenced and assembled 30 high-quality Malus genomes, representing 20 diploids and 10 polyploids across major evolutionary lineages and geographical regions. Phylogenomic analyses revealed ancient gene duplications and conversions, while six newly defined genome types, including an ancestral type shared by polyploid species, facilitated the detection of strong signals for extensive introgressions. The graph-based pan-genome captured shared and species-specific structural variations, facilitating the development of a molecular marker for apple scab resistance. Our pipeline for analyzing selective sweep identified a mutation in MdMYB5 having reduced cold and disease resistance during domestication. This study advances Malus genomics, uncovering genetic diversity and evolutionary insights while enhancing breeding for desirable traits.

Seeking consensus on the domestication concept

The domestication of plants and animals permitted the development of cities and social hierarchies, as well as fostering cultural changes that ultimately led humanity into the modern world. Despite the importance of this set of related evolutionary phenomena, scholars have not reached a consensus on what the earliest steps in the domestication process looked like, how long the seminal portions of the process took to unfold, or whether humans played a conscious role in parts or all of it. Likewise, many scholars find it difficult to disentangle the cultural processes of cultivation from the biological processes of domestication. Over the past decade, the prevailing views among scholars have begun to shift towards unconscious and protracted models of early domestication; however, the nomenclature used to discuss these changes has been stagnant. Discussions of early domestication remain bound up in prevailing definitions and preconceived ideas of what the process looked like. In this paper, we seek to break down definitions of domestication and to construct a definition that serves equal utility regardless of the views that researchers hold about the process.This article is part of the theme issue 'Unravelling domestication: multi-disciplinary perspectives on human and non-human relationships in the past, present and future'.

MdZFP7 integrates JA and GA signals via interaction with MdJAZ2 and MdRGL3a in regulating anthocyanin biosynthesis and undergoes degradation by the E3 ubiquitin ligase MdBRG3

Jasmonic acid (JA) and gibberellin (GA) coordinate many aspects of plant growth and development, including anthocyanin biosynthesis. However, the crossover points of JA and GA signals and the pathways through which they interact to regulate anthocyanin biosynthesis are poorly understood. Here, we investigated the molecular mechanism by which the zinc finger protein (ZFP) transcription factor Malus domestica ZFP7 (MdZFP7) regulates anthocyanin biosynthesis by integrating JA and GA signals at the transcriptional and post-translational levels. MdZFP7 is a positive regulator of anthocyanin biosynthesis, which fulfills its role by directly activating the expression of MdMYB1 and enhancing the transcriptional activation of MdWRKY6 on the target genes MdDFR and MdUF3GT. MdZFP7 integrates JA and GA signals by interacting with the JA repressor apple JASMONATE ZIM-DOMAIN2 (MdJAZ2) and the GA repressor apple REPRESSOR-of-ga1-3-like 3a (MdRGL3a). MdJAZ2 weakens the transcriptional activation of MdMYB1 by MdZFP7 and disrupts the MdZFP7-MdWRKY6 interaction, thereby reducing the anthocyanin biosynthesis promoted by MdZFP7. MdRGL3a contributes to the stimulation of anthocyanin biosynthesis by MdZFP7 by sequestering MdJAZ2 from the MdJAZ2-MdZFP7 complex. The E3 ubiquitin ligase apple BOI-related E3 ubiquitin-protein ligase 3 (MdBRG3), which is antagonistically regulated by JA and GA, targets the ubiquitination degradation of MdZFP7. The MdBRG3-MdZFP7 module moves the crosstalk of JA and GA signals from the realm of transcriptional regulation and into the protein post-translational modification. In conclusion, this study not only elucidates the node-role of MdZFP7 in the integration of JA and GA signals, but also describes the transcriptional and post-translational regulatory network of anthocyanin biosynthesis with MdZFP7 as the hub.

Epigenetic modification brings new opportunities for gene capture by transposable elements in allopolyploid Brassica napus

Polyploids are widespread in plants and are important drivers for evolution and biodiversity. Allopolyploidy activates transposable elements (TEs) and causes genomic shock. Plant genomes can regulate gene expression by changing the epigenetic modification of TEs, but the mechanism for TEs to capture genes remains to be explored. Helitron TEs used the 'peel-and-paste' mechanism to achieve gene capture. We identified 3156 capture events and 326 donor genes of Helitron TEs in Brassica napus (AnAnCnCn). The donor genes captured by TEs were related to the number, length, and location of their exons. The gene-capturing TEs carrying donor gene fragments were evenly distributed on the genome, and more than half of them were involved in the construction of pseudogenes, becoming the reserve force for polyploid evolution. Gene fragment copies enhanced information storage, providing opportunities for gene mutation and the formation of new genes. Simultaneously, the siRNAs targeting TEs may act on the donor genes due to siRNA crosstalk, and the gene methylation levels increased and the expression levels decreased. The genome sought a balance between sacrificing donor gene expression and silencing TEs, allowing TEs to hide in the genome. In addition, epigenetic modifications may temporarily relax the control of gene capture during allopolyploidization. Our study identified and characterized gene capture events in B. napus, analyzed the effects of DNA methylation and siRNA on gene capture events, and explored the regulation mechanism of gene expression by TE epigenetic modification during allopolyploidization, which will contribute to understanding the formation and evolution mechanism of allopolyploidy.

Combined analysis of lncRNAs and mRNAs associated with coloration and wax formation during 'Fumei' Apple development

'Fumei' apple is characterized by high anthocyanin content and thick wax layer. Long non-coding RNAs (lncRNAs) play essential roles in the growth and development of various plants via regulation of gene expression. This study explored the potential mechanism underlying anthocyanin accumulation and cuticular wax formation during the development of 'Fumei' apple fruit. The results demonstrated that anthocyanin accumulation correlates with fruit coloration, while wax content drives wax layer formation. A total of 6039 and 3410 differentially expressed genes (DEGs), as well as 230 and 131 differentially expressed lncRNAs (DELs) were identified in the M1/M2 and M2/M3 pairs, respectively, by using RNA-seq. In the M1/M2 pair, the DEGs were mainly enriched in the 'photosynthesis' and 'flavonoid biosynthesis' pathways; in the M2/M3 pair, the DEGs were significantly enriched in the 'photosynthesis' and 'cutin, suberine and wax biosynthesis' pathways. Furthermore, the structural and regulatory genes involved in anthocyanin and cuticular wax biosynthesis were investigated, and the potential lncRNAs and genes that may control the anthocyanin and cuticular wax biosynthesis were identified. This study provides candidate lncRNAs and potential regulatory genes associated with both the regulation of anthocyanins and wax during apple development.

Harnessing transposable elements for plant functional genomics and genome engineering

Transposable elements (TEs) constitute a large portion of many plant genomes and play important roles in regulating gene expression and in driving genome evolution and crop domestication. Despite advances in understanding the functions and mechanisms of TEs, a comprehensive review of their integrated knowledge and cutting-edge biotechnological applications of TEs is still needed. We provide a thorough overview that connects discoveries, mechanisms, and technologies associated with plant TEs. We discuss the identification and function of TEs driven by functional genomics, epigenetic regulation of TEs, and utilization of active TEs in plant functional genomics and genome engineering. In summary, expanding the knowledge and application of TEs will be beneficial to crop breeding and plant synthetic biology in the future.

Uncovering the breeding contribution of transposable elements from landraces to improved varieties through pan-genome-wide analysis in rice

Introduction

The rice improvement process, driven by modern breeding techniques, represents the second revolutionary advancement in rice agronomic traits, following domestication. Advances in pan-genomes and enhanced capacity for analyzing structural variations have increasingly highlighted their role in rice genetic improvement. Transposable element (TE) variants have been previously reported to influence rice genomic diversity during the domestication, but their contribution to the improvement from landraces to improved varieties remains unclear.

Methods

Here, we combined a high-quality pan-TE variation map, transcriptome profiles, and phenotypic data for 100 landraces and 92 improved varieties to investigate the contribution of TE variations to phenotypic improvement in rice.

Results

The total number and length of TE variations in improved varieties were significantly greater than those in rice landraces, particularly for Ty3-retrotransposons, LTR Copia and Helitron elements. Comparing landraces and improved varieties, 4,334 selective TEs were detected within or near 3,070 genes that were enriched in basic metabolism and development and stress resistance. Among the 14,076 differentially expressed genes between the two groups, the expression level of 3,480 (24.7%) genes were significantly associated with TE variations. Combining with haplotype analysis, we demonstrated potential patterns of how TEs affect gene expression variation and thereby participate in the improvement of important agronomic traits in rice.

Discussion

Collectively, our results highlight the contributions of TE variations to rice improvement in shaping the genetic basis of modern rice varieties and will facilitate the exploration of superior genes and advance molecular breeding efforts in rice.

Mitochondrial genome assembly of the Chinese endemic species of Camellia luteoflora and revealing its repetitive sequence mediated recombination, codon preferences and MTPTs

Camellia luteoflora Y.K. Li ex Hung T. Chang & F.A. Zeng belongs to the Camellia L. genus (Theaceae Mirb.). As an endemic, rare, and critically endangered species in China, it holds significant ornamental and economic value, garnering global attention due to its ecological rarity. Despite its conservation importance, genomic investigations on this species remain limited, particularly in organelle genomics, hindering progress in phylogenetic classification and population identification. In this study, we employed high-throughput sequencing to assemble the first complete mitochondrial genome of C. luteoflora and reannotated its chloroplast genome. Through integrated bioinformatics analyses, we systematically characterized the mitochondrial genome's structural organization, gene content, interorganellar DNA transfer, sequence variation, and evolutionary relationships.Key findings revealed a circular mitochondrial genome spanning 587,847 bp with a GC content of 44.63%. The genome harbors70 unique functional genes, including 40 protein-coding genes (PCGs), 27 tRNA genes, and 3 rRNA genes. Notably, 9 PCGs contained 22 intronic regions. Codon usage analysis demonstrated a pronounced A/U bias in synonymous codon selection. Structural features included 506 dispersed repeats and 240 simple sequence repeats. Comparative genomics identified 19 chloroplast-derived transfer events, contributing 29,534 bp (3.77% of total mitochondrial DNA). RNA editing prediction revealed 539 C-to-T conversion events across PCGs. Phylogenetic reconstruction using mitochondrial PCGs positioned C. luteoflora in closest evolutionary proximity to Camellia sinensis var. sinensis. Selection pressure analysis (Ka/Ks ratios < 1 for 11 PCGs) and nucleotide diversity assessment (Pi values: 0-0.00711) indicated strong purifying selection and low sequence divergence.This study provides the first comprehensive mitochondrial genomic resource for C. luteoflora, offering critical insights for germplasm conservation, comparative organelle genomics, phylogenetic resolution, and evolutionary adaptation studies in Camellia species.

A LTR retrotransposon insertion leads to leafy phenotype in maize by elevating ZmOM66 expression

Leafy (Lfy1) is a classical dominant mutant showing more leaf number above primary ear and later flowering time in maize, but the causal gene together with its underlying genetic mechanism are unknown. Here, we report the cloning of Lfy1 mutant, and find that a retrotransposon insertion leads to leafy phenotype by elevating expression of its neighboring gene ZmOM66. ZmOM66 encodes an AAA+ ATPase that locate in mitochondria and interacts with itself. ZmOM66 overexpression affects the starch degradation, as well as contents of glucose, pyruvic acid, trehalose-6-phosphate, and TCA cycle related amino acids, and influences expression patterns of circadian clock genes. Moreover, expressions of floral related genes, including photoperiod regulated gene ZmPHYB1, integrator genes ZCN7, ZNC8 and ZCN12, and floral meristem identity genes ZMM4, ZMM15, and MASD67, are also significantly decreased by ZmOM66 overexpression. These results deepen our understanding of the regulatory mechanism of floral transition and leaf number in plant.

Chromosome-level genome assembly assisting for dissecting mechanism of anthocyanin regulation in kiwifruit (Actinidia arguta)

Actinidia arguta is a newly emerged, commercially cultivated Actinidia species. A. arguta has a beautiful appearance and is rich in anthocyanin, and is thus highly welcomed by consumers. However, the mechanism of anthocyanin regulation in A. arguta remains unclear. In this study, we assembled the nearly complete genome of the first red A. arguta cultivar, 'Tianyuanhong', with an N50 of 21 Mb. Comparative genome analysis revealed a role of the expansion/contraction of gene families in the species-specific trait formation of A. arguta. Through verification of transient overexpression and stable transformation, RNA-seq analysis revealed a key bHLH transcription factor, AaBEE1, which negatively regulates anthocyanin biosynthesis. DAP-seq analysis combined with Y1H, EMSA, Chip-qPCR and LUC suggested that AaBEE1 binds to the G-box of the AaLDOX promoter and suppresses its expression. Overall, we assembled the genome of A. arguta and clarified its AaBEE1-AaLDOX module-mediated molecular mechanism of anthocyanin regulation.

Transcription factor MdGTL1a accelerates starch degradation by promoting the MdBam8 expression in postharvest apple fruit

Starch degradation plays a central role in fruit ripening. The β-amylase (Bam) catalysts starch degradation of apple fruit. However, the molecular mechanism regulating Bam gene expression in apples remains unclear. Using yeast one-hybrid library screening, we identified a transcription factor MdGTL1a that directly binds to the MdBam8 promoter. This bind was verified by using an electrophoretic mobility shift assay and confirmed to enhance the promotor activity of MdBam8 by promoter-β-glucuronidase transactivation assay. Transient over-expression of MdGTL1a activated MdBam8 expression and further enhanced starch degradation in apple flesh. Subcellular localization analyses in tobacco protoplasts demonstrated that the nucleus was the exclusive location of the MdGTL1a-GFP fusion protein. Exogenous salicylic acid treatment decreased MdGTL1a expression and resulted in higher starch content in apples, which was consistent with the fruit ripening. It is concluded that salicylic acid treatment could enhance apple storage quality by inhibiting starch degradation through a crucial transcription factor, MdGTL1a.

Investigating the Mechanisms of Adventitious Root Formation in Semi-Tender Cuttings of Prunus mume: Phenotypic, Phytohormone, and Transcriptomic Insights

Mei (Prunus mume Sieb. et Zucc.) is a rare woody species that flowers in winter, yet its large-scale propagation is limited by the variable ability of cuttings to form adventitious roots (ARs). In this study, two cultivars were compared: P. mume 'Xiangxue Gongfen' (GF), which roots readily, and P. mume 'Zhusha Wanzhaoshui' (ZS), which is more recalcitrant. Detailed anatomical observations revealed that following cutting, the basal region expanded within 7 days, callus tissues had appeared by 14 days, and AR primordia emerged between 28 and 35 days. Notably, compared to the recalcitrant cultivar ZS, the experimental cultivar GF exhibited significantly enhanced callus tissue formation and AR primordia differentiation. Physiological analyses showed that the initial IAA concentration was highest at day 0, whereas cytokinin (tZR) and gibberellin (GA1) levels peaked at 14 days, with ABA gradually decreasing over time, resulting in increased IAA/tZR and IAA/GA1 ratios during the rooting process. Transcriptomic profiling across these time points identified significant upregulation of key genes (e.g., PmPIN3, PmLOG2, PmCKX5, PmIAA13, PmLAX2, and PmGA2OX1) and transcription factors (PmWOX4, PmSHR, and PmNAC071) in GF compared to ZS. Moreover, correlation analyses revealed that PmSHR expression is closely associated with IAA and tZR levels. Overexpression of PmSHR in tobacco further validated its role in enhancing lateral root formation. Together, these findings provide comprehensive insights into the temporal, hormonal, and genetic regulation of AR formation in P. mume, offering valuable strategies for improving its propagation.

Long-read genome sequencing reveals the sequence characteristics of pear self-incompatibility locus

The S-RNase-based self-incompatibility locus (S-locus) in Petunia species contains 16-20 F-box genes, which collaboratively function in the recognition and subsequent degradation of non-self S-RNases, while distinguishing them from self S-RNase. However, the number of S-locus F-box genes (SFBBs) physically interacted with non-self S-RNases remains uncertain in Pyrus species. Utilizing Pacbio long-read sequencing, we successfully assembled the genome of pear cultivar 'Yali' (Pyrus bretschneideri), and identified 19 SFBBs from the Pyrus S17-locus spanning approximately 1.78 Mb. Additionally, we identified 17-21 SFBBs from other Pyrus and Malus S-loci spanning a range of 1.35 to 2.64 Mb. Based on the phylogenetic analysis, it was determined that Pyrus and Malus SFBBs could be classified into 22 groups, denoted as I to XXII. At amino acid level, SFBBs within a given group exhibited average identities ranged from 88.9% to 97.9%. Notably, all 19 SFBBs from the S17-locus co-segregated with S17-RNase, with 18 of them being specifically expressed in pollen. Consequently, these 18 pollen-specifically expressed SFBBs are considered potential candidates for the pollen-S determinant. Intriguingly, out of the 18 pollen-specifically expressed SFBBs, eight demonstrated interactions with at least one non-self S-RNase, while the remaining SFBBs failed to recognize any S-RNase. These findings provide compelling evidence supporting the existence of a collaborative non-self-recognition system governing self-incompatibility in pear species.

Transposable Element Landscape in the Monotypic Species Barthea barthei (Hance) Krass (Melastomataceae) and Its Role in Ecological Adaptation

Transposable elements (TEs) are crucial for genome evolution and ecological adaptation, but their dynamics in non-model plants are poorly understood. Using genomic, transcriptomic, and population genomic approaches, we analyzed the TE landscape of Barthea barthei (Melastomataceae), a species distributed across tropical and subtropical southern China. We identified 64,866 TE copies (16.76% of a 235 Mb genome), dominated by Ty3/Gypsy retrotransposons (8.82%) and DNA/Mutator elements (2.7%). A genome-wide analysis revealed 13 TE islands enriched in genes related to photosynthesis, tryptophan metabolism, and stress response. We identified 3859 high-confidence TE insertion polymorphisms (TIPs), including 29 fixed insertions between red and white flower ecotypes, affecting genes involved in cell wall modification, stress response, and secondary metabolism. A transcriptome analysis of the flower buds identified 343 differentially expressed TEs between the ecotypes, 30 of which were near or within differentially expressed genes. The non-random distribution (primarily within 5 kb of genes) and association with adaptive traits suggest a significant role in B. barthei's successful colonization of diverse habitats. Our findings provide insights into how TEs contribute to plant genome evolution and ecological adaptation in tropical forests, particularly through their influence on regulatory networks governing stress response and development.

Comparative transcriptome analysis and transient assays revealed AaGST and AaBGAL, respectively, contribute to skin and flesh coloration in A. arguta

Actinidia arguta possesses different colors in the fruit skin and flesh, but the underlying mechanism has not yet been clarified. In this study, we conducted 36 samples RNA-seq to investigate the phenotypic expression of different fruit tissues (skin and flesh) in red and green A. arguta varieties during different coloring phases. GO and KEGG enrichment results of differentially expressed genes (DEGs) suggested that the red color of the skin and flesh was derived from anthocyanin transport and flesh softening, respectively. Weighted gene co-expression network analysis (WGCNA) revealed MEyellow and MEblack modules significantly correlated with skin and flesh coloration, and two genes, Glutathione S-transferases (AaGST) and β-galactosidases (AaBGAL), were identified as hub genes involved in different tissue-specific coloration. Transient overexpression in apples and kiwifruits confirmed the role of AaGST and AaBGAL in color formation. Our results preliminarily explore the mechanism of red color formation in different A. arguta fruit tissues and provide novel insights into red color formation.

Taming large-scale genomic analyses via sparsified genomics

Searching for similar genomic sequences is an essential and fundamental step in biomedical research. State-of-the-art computational methods performing such comparisons fail to cope with the exponential growth of genomic sequencing data. We introduce the concept of sparsified genomics where we systematically exclude a large number of bases from genomic sequences and enable faster and memory-efficient processing of the sparsified, shorter genomic sequences, while providing comparable accuracy to processing non-sparsified sequences. Sparsified genomics provides benefits to many genomic analyses and has broad applicability. Sparsifying genomic sequences accelerates the state-of-the-art read mapper (minimap2) by 2.57-5.38x, 1.13-2.78x, and 3.52-6.28x using real Illumina, HiFi, and ONT reads, respectively, while providing comparable memory footprint, 2x smaller index size, and more correctly detected variations compared to minimap2. Sparsifying genomic sequences makes containment search through very large genomes and large databases 72.7-75.88x (1.62-1.9x when indexing is preprocessed) faster and 723.3x more storage-efficient than searching through non-sparsified genomic sequences (with CMash and KMC3). Sparsifying genomic sequences enables robust microbiome discovery by providing 54.15-61.88x (1.58-1.71x when indexing is preprocessed) faster and 720x more storage-efficient taxonomic profiling of metagenomic samples over the state-of-the-art tool (Metalign).

Allelic variation in an expansin, MdEXP-A1, contributes to flesh firmness at harvest in apples

Flesh firmness is a core quality trait in apple breeding because of its correlation with ripening and storage. Quantitative trait loci (QTLs) were analyzed through bulked segregant analysis sequence (BSA-seq) and comparative transcriptome analysis (RNA-seq) to explore the genetic basis of firmness formation. In this study, phenotypic data were collected at harvest from 251 F1 hybrids derived from 'Ruiyang' and 'Scilate', the phenotype values of flesh firmness at harvest were extensively segregated for two consecutive years. A total of 11 candidate intervals were identified on chromosomes 03, 05, 06, 07, 13, and 16 via BSA-seq analysis. We characterized a major QTL on chromosome 16 and selected a candidate gene encoding expansin MdEXP-A1 by combining RNA-seq analysis. Furthermore, the genotype of Del-1166 (homozygous deletion) in the MdEXP-A1 promoter was closely associated with the super-hard phenotype of F1 hybrids, which could be used as a functional marker for marker-assisted selection (MAS) in apple. Functional identification revealed that MdEXP-A1 positively expedited fruit softening in both apple fruits and tomatoes that overexpressed MdEXP-A1. Moreover, the promoter sequence of TE-1166 was experimentally validated containing two binding motifs of MdNAC1, and the absence of the MdEXP-A1 promoter fragment reduced its transcription activity. MdNAC1 also promotes the expression of MdEXP-A1, indicating its potential modulatory role in quality breeding. These findings provide novel insight into the genetic control of flesh firmness by MdEXP-A1.

Integrated Transcriptomic and Metabolomic Analysis Revealed Regulatory Mechanisms on Flavonoids Biosynthesis in the Skin of Passion Fruit (Passiflora spp.)

Passion fruit is one of the most famous fruit crops in tropical and subtropical regions due to its high edible, medicinal, and ornamental value. Flavonoids, a class of plant secondary metabolites, have important health-related roles. In this study, a total of 151 flavonoid metabolites were identified, of which 25 key metabolites may be the main contributors to the purple phenotype. Using RNA sequencing, 11,180 differentially expressed genes (DEGs) were identified. Among these, 48 flavonoid biosynthesis genes (PAL, 4CL, C4H, CHS, CHI, F3H, DFR, ANS, and UFGT) and 123 transcription factors were identified. Furthermore, 12 distinct modules were identified through weighted gene coexpression network analysis, of which the brown module displays a robust positive correlation with numerous flavonoid metabolites. Overexpression of PeMYB114 significantly promoted flavonoids accumulation in tobacco leaves. Our study provided a key candidate gene for molecular breeding to improve color traits in passion fruit.

Malus sieversii: a historical, genetic, and conservational perspective of the primary progenitor species of domesticated apples

Apples are one of the most valued tree fruit crops around the world. Currently, a few highly popular and economically successful apple cultivars dominate the commercial production and serve as main genetic contributors to the development of new apple cultivars. This limited level of genetic diversity grown as a clonally propagated monoculture renders the apple industry vulnerable to the wide range of weather events, pests, and pathogens. Wild apple species are an excellent source of beneficial alleles for the wide range of biotic and abiotic stressors challenging apple production. However, the biological barriers of breeding with small-fruited wild apples greatly limit their use. Using a closely related wild species of apple such as Malus sieversii can improve the efficiency of breeding efforts and broaden the base of available genetics. M. sieversii is the main progenitor of the domesticated apple, native to Central Asia. The similarity of fruit morphology to domesticated apples and resistances to abiotic and biotic stresses makes it appealing for apple breeding programs. However, this important species is under threat of extinction in its native range. Preserving the wild apple forests in Central Asia is vital for ensuring the sustainable protection of this important genetic resource. The insufficient awareness about the complete range of challenges and opportunities associated with M. sieversii hinders the maximization of its potential benefits. This review aims to provide comprehensive information on the cultural and historical context of M. sieversii, current genetic knowledge for breeding, and the conservation challenges of wild apple forests.

A transposon DNA/hAT-Ac insertion promotes the formation of yellow tepals in lotus (Nelumbo)

Yellow tepal is a unique trait of the American lotus (Nelumbo lutea), and all yellow lotus cultivars in the market possess genetic material from the American lotus. However, the formation of yellow tepals in lotus and the genetic mechanism of their formation remain unclear. In this study, we identified a transposon DNA/hAT-Ac, located within the promoter region of an R2R3-MYB transcription factor, MYB12, by comparing the insertion patterns of transposons in the genomes of American and Asian lotus (Nelumbo nucifera). The transposon was found exclusively in yellow lotus cultivars and not in red or white lotus. The insertion of DNA/hAT-Ac facilitated the specific expression of MYB12 in the yellow lotus tepals. Transient expression in lotus tepals, dual-luciferase, and yeast one-hybrid assays demonstrated that MYB12 promotes the accumulation of carotenoids and flavonols by activating the expression of genes involved in carotenoid and flavonols biosynthesis, and it directly binds to the promoters of PSY and FLS. Our results indicated that the transposon DNA/hAT-Ac-mediated specific expression of MYB12 is crucial for the formation of yellow tepals in lotus, and the findings provide a theoretical basis for the breeding of yellow lotus cultivars.

Plant anthocyanins: Classification, biosynthesis, regulation, bioactivity, and health benefits

Anthocyanins are naturally water-soluble pigments of plants, which can be pink, orange, red, purple, or blue. Anthocyanins belong to a subcategory of flavonoids known as polyphenols and are consumed in plant-based foods. The antioxidant properties of anthocyanins benefit human health. However, there has been no comprehensive review of the classification, distribution, and biosynthesis of anthocyanins and their regulation in plants, along with their potential health benefits. In this review, we provide a systematic synthesis of recent progress in anthocyanin research, specifically focusing on the classification, biosynthetic pathways, regulatory mechanisms, bioactivity, and health benefits. We bridge the gaps in understanding anthocyanin biological significance and potential applications. Furthermore, we discuss future directions for anthocyanin research, such as biotechnology, bioavailability, and the integration of artificial intelligence. We highlight pivotal research questions that warrant further exploration in the field of anthocyanin research.

Genome sequencing of 'Fuji' apple clonal varieties reveals genetic mechanism of the spur-type morphology

Somatic variations can give rise to bud sports with advantageous traits, serving as the foundation for bud sport breeding in perennial plants. Here, we report a fully phased genome assembly of 'Fuji' apple, enabling comprehensive identification of somatic variants across 74 clonally propagated 'Fuji' varieties. Phylogenetic analysis indicates that spur-type and early-maturation traits in 'Fuji' sport varieties arise from multiple independent events. Several putative functional somatic variants have been identified, including a spur-type-specific deletion in the promoter of the TCP transcription factor gene MdTCP11. DNA methylation level of the deletion-associated miniature inverted-repeat transposable element is lower in spur-type varieties compared to standard-type varieties, while the expression of MdTCP11 is significantly higher. Overexpression of MdTCP11 in apple decreases plant height, highlighting its important role in the development of spur-type apple varieties. This study sheds light on the cloning history of 'Fuji' and provides valuable resources for apple breeding.

Upregulation of PECTATE LYASE5 by a NAC transcription factor promotes fruit softening in apple

Flesh firmness is a critical breeding trait that determines consumer selection, shelf life, and transportation. The genetic basis controlling firmness in apple (Malus × domestica Borkh.) remains to be fully elucidated. We aimed to decipher genetic variance for firmness at harvest and develop potential molecular markers for marker-assisted breeding. Maturity firmness for 439 F1 hybrids from a cross of "Cripps Pink" and "Fuji" was determined in 2016 and 2017. The phenotype segregated extensively, with a Gaussian distribution. In a combined bulked segregant analysis (BSA) and RNA-sequencing analysis, 84 differentially expressed genes were screened from the 10 quantitative trait loci regions. Interestingly, next-generation re-sequencing analysis revealed a Harbinger-like transposon element insertion upstream of the candidate gene PECTATE LYASE5 (MdPL5); the genotype was associated with flesh firmness at harvest. The presence of this transposon repressed MdPL5 expression and was closely linked to the extra-hard phenotype. MdPL5 was demonstrated to promote softening in apples and tomatoes. Subsequently, using the MdPL5 promoter as bait, MdNAC1-L was identified as a transcription activator that positively regulates ripening and softening in the developing fruit. We also demonstrated that MdNAC1-L could induce the up-regulation of MdPL5, MdPG1, and the ethylene-related genes MdACS1 and MdACO1. Our findings provide insight into TE-related genetic variation and the PL-mediated regulatory network for the firmness of apple fruit.

Comprehensive analysis of AHL genes in Malus domestica reveals the critical role of MdAHL6 in flowering induction

AT-hook motif nuclear localized (AHL) genes are crucial in various biological processes, yet the AHL gene family in apples has remained largely unexplored. In this study, we isolated 36 MdAHL genes from the apple genome and grouped them into two distinct clades. We characterized the gene structure, conserved motifs, protein biochemical properties, and promoter regions of the MdAHL genes. Transcriptional analysis revealed that MdAHL genes are preferentially and predominantly expressed in flowers and leaves. Notably, during the floral induction phase, the MdAHL6 gene exhibited remarkably high transcriptional activity. Overexpression of MdAHL6 resulted in shortened hypocotyls and delayed flowering by regulating hypocotyl- and floral-related genes. Y1H, EMSA, GUS activity, and molecular docking assays revealed that MdAHL6 directly binds to AT-rich regions, inhibiting the expression of FLOWERING LOCUS T (MdFT). Furthermore, Y2H, pull-down, and BiFC assays demonstrated a physical interaction between MdAHL6 and the class II knotted-like transcription factor MdKNOX19, which significantly enhances the inhibitory effect of MdAHL6 on MdFT expression. This comprehensive initial analysis unveils the critical role of the MdKNOX19-MdAHL6-MdFT module in flowering induction and lays a theoretical foundation for future functional exploration.

Identification and Mining of Functional Components of Polyphenols in Fruits of Malus Germplasm Resources Based on Multivariate Analysis

Polyphenols are important functional components that have anti-cancer and anti-inflammatory effects. Apple fruit is rich in polyphenols and is one of the dietary sources of polyphenols. The polyphenol components and contents of the peel and pulp of 74 Malus sieversii (Led.) Roem. and 26 Chinese Malus germplasm resources were determined using ultra-high-phase chromatography (UPLC) and liquid chromatography-mass spectrometry (LC-MS). The results showed that 34 components were detected in the peel and 30 in the flesh, and that the polyphenol components and contents of the different germplasm resources were significantly different; the polyphenol content of Malus sieversii (Led.) Roem. was significantly higher than that of the other local varieties, and the polyphenol content in the peel was also higher than that in the flesh. Rutin, quercetin 3-O-arabopyranoside, kaempferol 3-O-rutinoside, and peonidin 3-O-galactoside were detected only in the peel. The total polyphenol content in the peel ranged from 949.76 to 5840.06 mg/kg, and the polyphenol content in the pulp ranged from 367.31 to 5123.10 mg/kg. The cluster analysis of polyphenol components and contents in peel and pulp showed that 100 Malus germplasm resources could be grouped into four categories. Principal component analysis of 34 kinds and 30 kinds of polyphenols in peel and pulp of 100 resources was performed. If the eigenvalue is greater than 1, eight and seven principal components are extracted, respectively. Five Malus resources with high polyphenol content in the peel and pulp were selected: 'XY-77' (peel: 5840.06 mg/kg, pulp: 5123.10 mg/kg; 'LF-09' (peel: 4692.63 mg/kg, pulp: 3729.79 mg/kg); '2012-5' (peel: 4377.61 mg/kg, pulp: 3847.54 mg/kg); '29028' (peel: 5088.05 mg/kg, pulp: 3994.61 mg/kg); and '11-01' (peel: 5154.45 mg/kg, pulp: 3616.15 mg/kg). These results provide us with information regarding the polyphenol composition and content of the wild apple resources and local cultivars. The high polyphenol content resources obtained by screening can be used as raw materials for the extraction of polyphenol components and functional fruit juice processing and can also be used as parents for functional fruit creation and variety breeding.

The pineapple reference genome: Telomere-to-telomere assembly, manually curated annotation, and comparative analysis

Pineapple is the third most crucial tropical fruit worldwide and available in five varieties. Genomes of different pineapple varieties have been released to date; however, none of them are complete, with all exhibiting substantial gaps and representing only two of the five pineapple varieties. This significantly hinders the advancement of pineapple breeding efforts. In this study, we sequenced the genomes of three varieties: a wild pineapple variety, a fiber pineapple variety, and a globally cultivated edible pineapple variety. We constructed the first gap-free reference genome (Ref) for pineapple. By consolidating multiple sources of evidence and manually revising each gene structure annotation, we identified 26,656 protein-coding genes. The BUSCO evaluation indicated a completeness of 99.2%, demonstrating the high quality of the gene structure annotations in this genome. Utilizing these resources, we identified 7,209 structural variations across the three varieties. Approximately 30.8% of pineapple genes were located within ±5 kb of structural variations, including 30 genes associated with anthocyanin synthesis. Further analysis and functional experiments demonstrated that the high expression of AcMYB528 aligns with the accumulation of anthocyanins in the leaves, both of which may be affected by a 1.9-kb insertion fragment. In addition, we developed the Ananas Genome Database, which offers data browsing, retrieval, analysis, and download functions. The construction of this database addresses the lack of pineapple genome resource databases. In summary, we acquired a seamless pineapple reference genome with high-quality gene structure annotations, providing a solid foundation for pineapple genomics and a valuable reference for pineapple breeding.

The identification and analysis of meristematic mutations within the apple tree that developed the RubyMac sport mutation

BACKGROUND

Understanding the molecular basis of sport mutations in fruit trees has the potential to accelerate generation of improved cultivars.

RESULTS

For this, we analyzed the genome of the apple tree that developed the RubyMac phenotype through a sport mutation that led to the characteristic fruit coloring of this variety. Overall, we found 46 somatic mutations that distinguished the mutant and wild-type branches of the tree. In addition, we found 54 somatic gene conversions (i.e., loss-of-heterozygosity mutations) that also distinguished the two parts of the tree. Approximately 20% of the mutations were specific to individual cell lineages, suggesting that they originated from the corresponding meristematic layers. Interestingly, the de novo mutations were enriched for GC =  > AT transitions while the gene conversions showed the opposite bias for AT =  > GC transitions, suggesting that GC-biased gene conversions have the potential to counteract the AT-bias of de novo mutations. By comparing the gene expression patterns in fruit skins from mutant and wild-type branches, we found 56 differentially expressed genes including 18 involved in anthocyanin biosynthesis. While none of the differently expressed genes harbored a somatic mutation, we found that some of them in regions of the genome that were recently associated with natural variation in fruit coloration.

CONCLUSION

Our analysis revealed insights in the characteristics of somatic change, which not only included de novo mutations but also gene conversions. Some of these somatic changes displayed strong candidate mutations for the change in fruit coloration in RubyMac.

Impact of Chromosomal Fusion and Transposable Elements on the Genomic Evolution and Genetic Diversity of Ilex Species

The genus Ilex belongs to the sole family and is the single genus within the order Aquifoliales, exhibiting significant phenotypic diversity. However, the genetic differences underlying these phenotypic variations have rarely been studied. In this study, collinearity analyses of three Ilex genomes, Ilex latifolia Thunb., Ilex polyneura (Hand.-Mazz.) S. Y. Hu, and Ilex asprella Champ. ex Benth., indicated a recent fusion event contributing to the reduction of chromosomes in I. asprella. Comparative genome analyses showed slight differences in gene annotation among the three species, implying a minimal disruption of genes following chromosomal fusion in I. asprella. Comprehensive annotation of transposable elements (TEs) revealed that TEs constitute a significant portion of the Ilex genomes, with LTR transposons being predominant. TEs exhibited an inverse relationship with gene density, potentially influencing gene regulation and chromosomal architecture. TE insertions were shown to affect the conformation and binding sites of key genes such as 7-deoxyloganetin glucosyltransferase and transmembrane kinase (TMK) genes, highlighting potential functional impacts. The structural variations caused by TE insertions suggest significant roles in the evolutionary dynamics, leading to either loss or gain of gene function. This study underscores the importance of TEs in shaping the genomic landscape and evolutionary trajectories of Ilex species.

Comparative Analysis of Transposable Elements in the Genomes of Citrus and Citrus-Related Genera

Transposable elements (TEs) significantly contribute to the evolution and diversity of plant genomes. In this study, we explored the roles of TEs in the genomes of Citrus and Citrus-related genera by constructing a pan-genome TE library from 20 published genomes of Citrus and Citrus-related accessions. Our results revealed an increase in TE content and the number of TE types compared to the original annotations, as well as a decrease in the content of unclassified TEs. The average length of TEs per assembly was approximately 194.23 Mb, representing 41.76% (Murraya paniculata) to 64.76% (Citrus gilletiana) of the genomes, with a mean value of 56.95%. A significant positive correlation was found between genome size and both the number of TE types and TE content. Consistent with the difference in mean whole-genome size (39.83 Mb) between Citrus and Citrus-related genera, Citrus genomes contained an average of 34.36 Mb more TE sequences than Citrus-related genomes. Analysis of the estimated insertion time and half-life of long terminal repeat retrotransposons (LTR-RTs) suggested that TE removal was not the primary factor contributing to the differences among genomes. These findings collectively indicate that TEs are the primary determinants of genome size and play a major role in shaping genome structures. Principal coordinate analysis (PCoA) of Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) identifiers revealed that the fragmented TEs were predominantly derived from ancestral genomes, while intact TEs were crucial in the recent evolutionary diversification of Citrus. Moreover, the presence or absence of intact TEs near the AdhE superfamily was closely associated with the bitterness trait in the Citrus species. Overall, this study enhances TE annotation in Citrus and Citrus-related genomes and provides valuable data for future genetic breeding and agronomic trait research in Citrus.

AcMYB96 promotes anthocyanin accumulation in onion (Allium cepa L) without forming the MBW complex

Anthocyanins are major flavonoid compounds with established health benefits. Although the molecular mechanisms of MYB transcription factors (TFs) within the MYB-basic helix-loop-helix (bHLH)-WD-repeat protein (MBW) complex in anthocyanin biosynthesis have been revealed, the functions of other MYB TFs that are unable to form the MBW complex in this process remain unclear. In this study, we uncovered and extensively characterized an R2R3-MYB TF in onion (Allium cepa L.), named AcMYB96, which was identified as a potential anthocyanin activator. AcMYB96 was classified into subgroup 1 of the R2R3-MYB TF family and lacked the conserved sequences required for interactions with bHLH IIIf TFs. Consistently, yeast two-hybrid assays showed that AcMYB96 did not interact with any bHLH IIIf TFs examined, including AcB2 and AtTT8. The transcription pattern of AcMYB96 correlated with the level of anthocyanin accumulation, and its role in activating anthocyanin biosynthesis was confirmed through overexpression in the epithelial cells of onion bulbs and Arabidopsis. Yeast one-hybrid, electrophoretic mobility shift, and promoter transactivation assays further demonstrated that AcMYB96 promoted anthocyanin biosynthesis by binding to the promoters of the chalcone synthase (AcCHS1), anthocyanidin synthase (AcANS), and UDP-glucose-flavonoid 3-O-glucosyltransferase (AcUFGT) genes, thereby activating their expression independent of bHLH IIIf TFs. These results demonstrate that AcMYB96 activates anthocyanin biosynthesis without forming the MBW complex, providing a theoretical foundation to further enrich the gene resources for promoting anthocyanin accumulation and breeding red onions with high anthocyanin content.

The genome assembly of Carex breviculmis provides evidence for its phylogenetic localization and environmental adaptation

BACKGROUND AND AIMS

Carex breviculmis is a perennial herb with good resistance and is widely used for forage production and turf management. It is important in ecology, environmental protection and biodiversity conservation, but faces several challenges due to human activities. However, the absence of genome sequences has limited basic research and the improvement of wild plants.

METHODS

We annotated the genome of C. breviculmis and conducted a systematic analysis to explore its resistance to harsh environments. We also conducted a comparative analysis of Achnatherum splendens, which is similarly tolerant to harsh environments.

KEY RESULTS

The assembled the genome comprises 469.01 Mb, revealing 37 372 genes with a BUSCO completeness score of 99.0 %. The genome has 52.03 % repetitive sequences, primarily influenced by recent LTR insertions that have contributed to its expansion. Phylogenetic analysis suggested that C. breviculmis diverged from C. littledalei ~6.61 million years ago. Investigation of repetitive sequences and expanded gene families highlighted a rapid expansion of tandem duplicate genes, particularly in areas related to sugar metabolism, synthesis of various amino acids, and phenylpropanoid biosynthesis. Additionally, our analysis identified crucial genes involved in secondary metabolic pathways, such as glycolysis, phenylpropanoid biosynthesis and amino acid metabolism, which have undergone positive selection. We reconstructed the sucrose metabolic pathway and identified significant gene expansions, including 16 invertase, 9 sucrose phosphate synthase and 12 sucrose synthase genes associated with sucrose metabolism, which showed varying levels of expansion.

CONCLUSIONS

The expansion of these genes, coupled with subsequent positive selection, contributed to the ability of C. breviculmis to adapt to environmental stressors. This study lays the foundation for future research on the evolution of Carex plants, their environmental adaptations, and potential genetic breeding.

Gene Duplication and Functional Diversification of MADS-Box Genes in Malus × domestica following WGD: Implications for Fruit Type and Floral Organ Evolution

The evolution of the MADS-box gene family is essential for the rapid differentiation of floral organs and fruit types in angiosperms. Two key processes drive the evolution of gene families: gene duplication and functional differentiation. Duplicated copies provide the material for variation, while advantageous mutations can confer new functions on gene copies. In this study, we selected the Rosaceae family, which includes a variety of fruit types and flower organs, as well as species that existed before and after whole-genome duplication (WGD). The results indicate that different fruit types are associated with different copies of MADS-box gene family duplications and WGD events. While most gene copies derived from WGD have been lost, MADS-box genes not only retain copies derived from WGD but also undergo further gene duplication. The sequences, protein structures, and expression patterns of these gene copies have undergone significant differentiation. This work provides a clear example of MADS-box genes in the context of gene duplication and functional differentiation, offering new insights into the evolution of fruit types and floral organs.

Why we thrive beneath a northern sky - genomic signals of selection in apple for adaptation to northern Sweden

Good understanding of the genomic regions underlying adaptation of apple to boreal climates is needed to facilitate efficient breeding of locally adapted apple cultivars. Proper infrastructure for phenotyping and evaluation is essential for identification of traits responsible for adaptation, and dissection of their genetic composition. However, such infrastructure is costly and currently not available for the boreal zone of northern Sweden. Therefore, we used historical pomological data on climate adaptation of 59 apple cultivars and whole genome sequencing to identify genomic regions that have undergone historical selection among apple cultivars recommended for cultivation in northern Sweden. We found the apple collection to be composed of two ancestral groups that are largely concordant with the grouping into 'hardy' and 'not hardy' cultivars based on the pomological literature. Using a number of genome-wide scans for signals of selection, we obtained strong evidence of positive selection at a genomic region around 29 MbHFTH1 of chromosome 1 among apple cultivars in the 'hardy' group. Using phased genotypic data from the 20 K apple Infinium® SNP array, we identified haplotypes associated with the two cultivar groups and traced transmission of these haplotypes through the pedigrees of some apple cultivars. This demonstrates that historical data from pomological literature can be analyzed by population genomic approaches as a step towards revealing the genomic control of a key property for a horticultural niche market. Such knowledge is needed to facilitate efficient breeding strategies for development of locally adapted apple cultivars in the future. The current study illustrates the response to a very strong selective pressure imposed on tree crops by climatic factors, and the importance of genetic research on this topic and feasibility of breeding efforts in the light of the ongoing climate change.

Genome-wide identification of starch phosphorylase gene family in Rosa chinensis and expression in response to abiotic stress

Chinese rose (Rosa chinensis) is an important ornamental plant, with economic, cultural, and symbolic significance. During the application of outdoor greening, adverse environments such as high temperature and drought are often encountered, which affect its application scope and ornamental quality. The starch phosphorylase (Pho) gene family participate in the synthesis and decomposition of starch, not only related to plant energy metabolism, but also plays an important role in plant stress resistance. The role of Pho in combating salinity and high temperature stress in R. chinensis remains unknown. In this work, 4 Phos from R. chinensis were detected with Pfam number of Pho (PF00343.23) and predicted by homolog-based prediction (HBP). The Phos are characterized by sequence lengths of 821 to 997 bp, and the proteins are predicted to subcellularly located in the plastid and cytoplasm. The regulatory regions of the Phos contain abundant stress and phytohormone-responsive cis-acting elements. Based on transcriptome analysis, the Phos were found to respond to abiotic stress factors such as drought, salinity, high temperature, and plant phytohormone of jasmonic acid and salicylic acid. The response of Phos to abiotic stress factors such as salinity and high temperature was confirmed by qRT-PCR analysis. To evaluate the genetic characteristics of Phos, a total of 69 Phos from 17 species were analyzed and then classified into 3 groups in phylogenetic tree. The collinearity analysis of Phos in R. chinensis and other species was conducted for the first time. This work provides a view of evolution for the Pho gene family and indicates that Phos play an important role in abiotic stress response of R. chinensis.

A haplotype-resolved genome assembly of Malus domestica 'Red Fuji'

The 'Red Fuji' apple (Malus domestica), is one of the most important and popular economic crops worldwide in the fruit industry. Using PacBio HiFi long reads and Hi-C reads, we assembled a high-quality haplotype-resolved genome of 'Red Fuji', with sizes of 668.7 and 668.8 Mb, and N50 sizes of 34.1 and 31.4 Mb. About 97.2% of sequences were anchored in 34 chromosomes. We annotated both haploid genomes, identifying a total of 95,439 protein-coding genes in the two haplotype genomes, with 98% functional annotation. The haplotype-resolved genome of 'Red Fuji' apple stands as a precise benchmark for an array of analyses, such as comparative genomics, transcriptomics, and allelic expression studies. This comprehensive resource is paramount in unraveling variations in allelic expression, advancing quality improvements, and refining breeding efforts.

A pan-TE map highlights transposable elements underlying domestication and agronomic traits in Asian rice

Transposable elements (TEs) are ubiquitous genomic components and hard to study due to being highly repetitive. Here we assembled 232 chromosome-level genomes based on long-read sequencing data. Coupling the 232 genomes with 15 existing assemblies, we developed a pan-TE map comprising both cultivated and wild Asian rice. We detected 177 084 high-quality TE variations and inferred their derived state using outgroups. We found TEs were one source of phenotypic variation during rice domestication and differentiation. We identified 1246 genes whose expression variation was associated with TEs but not single-nucleotide polymorphisms (SNPs), such as OsRbohB, and validated OsRbohB's relative expression activity using a dual-Luciferase (LUC) reporter assays system. Our pan-TE map allowed us to detect multiple novel loci associated with agronomic traits. Collectively, our findings highlight the contributions of TEs to domestication, differentiation and agronomic traits in rice, and there is massive potential for gene cloning and molecular breeding by the high-quality Asian pan-TE map we generated.

A phased genome of the highly heterozygous 'Texas' almond uncovers patterns of allele-specific expression linked to heterozygous structural variants

The vast majority of traditional almond varieties are self-incompatible, and the level of variability of the species is very high, resulting in a high-heterozygosity genome. Therefore, information on the different haplotypes is particularly relevant to understand the genetic basis of trait variability in this species. However, although reference genomes for several almond varieties exist, none of them is phased and has genome information at the haplotype level. Here, we present a phased assembly of genome of the almond cv. Texas. This new assembly has 13% more assembled sequence than the previous version of the Texas genome and has an increased contiguity, in particular in repetitive regions such as the centromeres. Our analysis shows that the 'Texas' genome has a high degree of heterozygosity, both at SNPs, short indels, and structural variants level. Many of the SVs are the result of heterozygous transposable element insertions, and in many cases, they also contain genic sequences. In addition to the direct consequences of this genic variability on the presence/absence of genes, our results show that variants located close to genes are often associated with allele-specific gene expression, which highlights the importance of heterozygous SVs in almond.

Transposable elements in Rosaceae: insights into genome evolution, expression dynamics, and syntenic gene regulation

Transposable elements (TEs) exert significant influence on plant genomic structure and gene expression. Here, we explored TE-related aspects across 14 Rosaceae genomes, investigating genomic distribution, transposition activity, expression patterns, and nearby differentially expressed genes (DEGs). Analyses unveiled distinct long terminal repeat retrotransposon (LTR-RT) evolutionary patterns, reflecting varied genome size changes among nine species over the past million years. In the past 2.5 million years, Rubus idaeus showed a transposition rate twice as fast as Fragaria vesca, while Pyrus bretschneideri displayed significantly faster transposition compared with Crataegus pinnatifida. Genes adjacent to recent TE insertions were linked to adversity resistance, while those near previous insertions were functionally enriched in morphogenesis, enzyme activity, and metabolic processes. Expression analysis revealed diverse responses of LTR-RTs to internal or external conditions. Furthermore, we identified 3695 pairs of syntenic DEGs proximal to TEs in Malus domestica cv. 'Gala' and M. domestica (GDDH13), suggesting TE insertions may contribute to varietal trait differences in these apple varieties. Our study across representative Rosaceae species underscores the pivotal role of TEs in plant genome evolution within this diverse family. It elucidates how these elements regulate syntenic DEGs on a genome-wide scale, offering insights into Rosaceae-specific genomic evolution.

A chromosome-level genome assembly of Chinese quince (Pseudocydonia sinensis)

Introduction

Pseudocydonia sinensis, also known as Chinese quince, is a perennial shrub or small tree highly valued for its edibility and medicinal properties.

Method

This study presents the first chromosome-level genome assembly of P. sinensis, achieved using HiFi sequencing and Hi-C scaffolding technology.

Results

The assembly resulted in a high-quality genome of 576.39 Mb in size. The genome was anchored to 17 pseudo-chromosomes, with a contig N50 of 27.6 Mb and a scaffold N50 of 33.8 Mb. Comprehensive assessment using BUSCO, CEGMA and BWA tools indicates the high completeness and accuracy of the genome assembly. Our analysis identified 116 species-specific genes, 1196 expanded genes and 1109 contracted genes. Additionally, the distribution of 4DTv values suggests that the most recent duplication event occurred before the divergence of P. sinensis from both Chaenomeles pinnatifida and Pyrus pyrifolia.

Discussion

The assembly of this high-quality genome provides a valuable platform for the genetic breeding and cultivation of P. sinensis, as well as for the comparison of the genetic complexity of P. sinensis with other important crops in the Rosaceae family.

The chromosome-level genome assembly of the dwarfing apple interstock Malus hybrid 'SH6'

Malus hybrid 'SH6' (M. honanensis × M. domestica)is a commonly used apple interstock in China, known for its excellent dwarfing characteristics and cold tolerance. In this study, a combined strategy utilizing PacBio HiFi, Hi-C and parental resequencing data were employed to assemble two haploid genomes for 'SH6'. After chromosome anchoring, the final hapH genome size was 596.63 Mb, with a contig N50 of 34.38 Mb. The hapR genome was 649.37 Mb, with a contig N50 of 36.84 Mb. Further analysis predicted that repeated sequences made up 59.69% and 62.52% of the entire genome, respectively. Gene annotations revealed 45,435 genes for hapH and 48,261 genes for hapR. Combined with genomic synteny we suggest that the hapR genome originates from its maternal parent M. domestica cv. Ralls Janet, while the hapH genome comes from its paternal parent, M. honanensis. The assembled genome significantly contributes to the discovery of genes associated with apple dwarfing and the molecular mechanisms governing them.

Sequence and epigenetic variations of R2R3-MYB transcription factors determine the diversity of taproot skin and flesh colors in different cultivated types of radish (Raphanus sativus L.)

KEY MESSAGE

This study found that three paralogous R2R3-MYB transcription factors exhibit functional divergence among different subspecies and cultivated types in radish. Cultivated radish taproots exhibit a wide range of color variations due to unique anthocyanin accumulation patterns in various tissues. This study investigated the universal principles of taproot color regulation that developed during domestication of different subspecies and cultivated types. The key candidate genes RsMYB1 and RsMYB2, which control anthocyanin accumulation in radish taproots, were identified using bulked segregant analysis in two genetic populations. We introduced the RsMYB1-RsF3'H-RsMYB1Met genetic model to elucidate the complex and unstable genetic regulation of taproot flesh color in Xinlimei radish. Furthermore, we analyzed the expression patterns of three R2R3-MYB transcription factors in lines with different taproot colors and investigated the relationship between RsMYB haplotypes and anthocyanin accumulation in a natural population of 56 germplasms. The results revealed that three paralogous RsMYBs underwent functional divergence during radish domestication, with RsMYB1 regulating the red flesh of Xinlimei radish, and RsMYB2 and RsMYB3 regulating the red skin of East Asian big long radish (R. sativus var. hortensis) and European small radish (R. sativus var. sativus), respectively. Moreover, RsMYB1-H1, RsMYB2-H10, and RsMYB3-H6 were identified as the primary haplotypes exerting regulatory functions on anthocyanin synthesis. These findings provide an understanding of the genetic mechanisms regulating anthocyanin synthesis in radish and offer a potential strategy for early prediction of color variations in breeding programs.

A 224-bp Indel in the Promoter of PeMYB114 Accounts for Anthocyanin Accumulation of Skin in Passion Fruit (Passiflora spp.)

Passion fruit (Passiflora spp.) is an important fruit tree in the family Passifloraceae. The color of the fruit skin, a significant agricultural trait, is determined by the content of anthocyanin in passion fruit. However, the regulatory mechanisms behind the accumulation of anthocyanin in different passion fruit skin colors remain unclear. In the study, we identified and characterized a R2R3-MYB transcription factor, PeMYB114, which functions as a transcriptional activator in anthocyanin biosynthesis. Yeast one-hybrid system and dual-luciferase analysis showed that PeMYB114 could directly activate the expression of anthocyanin structural genes (PeCHS and PeDFR). Furthermore, a natural variation in the promoter region of PeMYB114 alters its expression. PeMYB114purple accessions with the 224-bp insertion have a higher anthocyanin level than PeMYB114yellow accessions with the 224-bp deletion. The findings enhance our understanding of anthocyanin accumulation in fruits and provide genetic resources for genome design for improving passion fruit quality.

Chromosome-scale genome assembly and annotation of Cotoneaster glaucophyllus

Cotoneaster glaucophyllus is a semi-evergreen plant that blossoms in late summer, producing dense, attractive, fragrant white flowers with significant ornamental and ecological value. Here, a chromosome-scale genome assembly was obtained by integrating PacBio and Illumina sequencing data with the aid of Hi-C technology. The genome assembly was 563.3 Mb in length, with contig N50 and scaffold N50 values of ~6 Mb and ~31 Mb, respectively. Most (95.59%) of the sequences were anchored onto 17 pseudochromosomes (538.4 Mb). We predicted 35,856 protein-coding genes, 1,401 miRNAs, 655 tRNAs, 425 rRNAs, and 795 snRNAs. The functions of 34,967 genes (97.52%) were predicted. The availability of this chromosome-level genome will provide valuable resources for molecular studies of this species, facilitating future research on speciation, functional genomics, and comparative genomics within the Rosaceae family.