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Marker-assisted screening of resistance to fire blight, powdery mildew, and apple scab in local apple varieties from Uzbekistan.

Apple (Malus domestica Borkh.) is one of the most economically important fruit crops worldwide; however, its production is severely constrained by major diseases, including fire blight, powdery mildew, and apple scab. Breeding disease-resistant cultivars represents a sustainable alternative to chemical control, particularly through the effective utilization of local germplasm resources from Central Asia. This study aimed to evaluate the presence and distribution of resistance-associated alleles in local apple varieties from Uzbekistan using polymorphic DNA markers. A collection of local apple accessions was screened to identify markers linked to resistance against fire blight, powdery mildew, and apple scab. The analysis revealed substantial genetic variation in resistance gene combinations among the studied varieties. The fire blight-associated marker AE10-375 was detected in 79.8% of the accessions. For powdery mildew resistance, 75.2% of the varieties carried resistance alleles corresponding to both Pl1 and Pl2 genes. Screening for apple scab resistance demonstrated that Vfa2, Vfa1, and Rvi6 were the most prevalent genes, with Vfa2 detected in 95.4% of the accessions. Regional analysis indicated that accessions from Karakalpakstan exhibited the highest proportion of genotypes harboring markers associated with resistance to multiple diseases. Six local varieties-Atlas olma, Turkish, Xuboni, Krasniy jeleznyak, Shoyi olma, and Besh barmoq-were identified as carrying resistance-associated markers for all three diseases. These findings demonstrate that local apple germplasm from Uzbekistan represents a valuable genetic resource for resistance to economically important diseases. The identified genotypes provide promising donor material for breeding programs aimed at developing cultivars with durable, broad-spectrum resistance while reducing reliance on chemical control strategies.

Malus

Phased telomere-to-telomere reference genome and pangenome reveal an expansion of resistance genes during apple domestication.

The cultivated apple (Malus domestica Borkh.) is a cross-pollinated perennial fruit tree of great economic importance. Earlier versions of apple reference genomes were unphased, fragmented, and lacked comprehensive insights into the apple's highly heterozygous genome, which impeded advances in genetic studies and breeding programs. In this study, we assembled a haplotype-resolved telomere-to-telomere (T2T) reference genome for the diploid apple cultivar Golden Delicious. Subsequently, we constructed a pangenome based on 12 assemblies from wild and cultivated species to investigate the dynamic changes of functional genes. Our results revealed the gene gain and loss events during apple domestication. Compared with cultivated species, more gene families in wild species were significantly enriched in oxidative phosphorylation, pentose metabolic process, responses to salt, and abscisic acid biosynthesis process. Our analyses also demonstrated a higher prevalence of different types of resistance gene analogs (RGAs) in cultivars than their wild relatives, partially attributed to segmental and tandem duplication events in certain RGAs classes. Structural variations, mainly deletions and insertions, have affected the presence and absence of TIR-NB-ARC-LRR, NB-ARC-LRR, and CC-NB-ARC-LRR genes. Additionally, hybridization/introgression from wild species has also contributed to the expansion of resistance genes in domesticated apples. Our haplotype-resolved T2T genome and pangenome provide important resources for genetic studies of apples, emphasizing the need to study the evolutionary mechanisms of resistance genes in apple breeding.

Malus

Cis-regulatory variation in the MdCKX6 promoter is associated with allele-specific expression and fruit size in apple.

Fruit size is a key determinant of apple fruit quality and market value and is strongly influenced by phytohormone-regulated cell proliferation and expansion during early fruit development. Cytokinin oxidase/dehydrogenase (CKX) enzymes regulate cytokinin homeostasis by irreversibly degrading active cytokinins, but the contribution of natural variation in CKX genes to fruit size remains poorly understood. Here, we identified MdCKX6 as a candidate regulator of fruit growth in apple (Malus domestica). MdCKX6 exhibited pronounced allele-specific expression during fruit development in the cultivar 'Royal Gala'. Sequence analysis identified a promoter SNP associated with differential promoter activity and allele-specific expression. Genotyping of diverse apple cultivars and wild Malus accessions revealed a significant association between MdCKX6 promoter genotype and fruit size. Cultivars carrying low-expression alleles produced larger fruits, whereas high-expression alleles were associated with smaller fruits. To investigate gene function, MdCKX6 was overexpressed in tomato, resulting in reduced fruit size. Histological analyses of the transgenic tomato fruit revealed smaller pericarp cells. Transcriptome analysis of transgenic fruits revealed widespread changes in genes associated with cell-cycle regulation, cell wall modification, hormone-related processes, and transcriptional regulation. Together, these results identify MdCKX6 as a potential negative regulator of apple fruit growth and reveal an association between cis-regulatory variants, gene expression, and fruit size. This study provides new insights into the role of cytokinin metabolism in fruit development and highlights regulatory variation in MdCKX6 as a potential target for apple breeding.

Malus

High temperature induces MdGATA15 to suppress anthocyanin accumulation in apple peels.

Although GATA transcription factors are known to play broad roles in plant growth, development, and stress responses, their involvement in high-temperature-induced anthocyanin suppression remains largely unexplored. In this study, using "Otome" as the experimental material, we revealed the important role of MdGATA15 in inhibiting anthocyanin accumulation under high temperature through multiple molecular mechanisms. A series of physiological and biochemical experiments demonstrated that MdGATA15 directly binds to the promoters of anthocyanin activators MdMYB11, MdANS, and the transporter gene MdGSTF12, repressing their expression. Simultaneously, MdGATA15 activates the expression of the anthocyanin biosynthesis repressor MdMYB308, further enhancing the inhibition. Notably, MdGATA15 binds to its own promoter, forming a positive feedback loop that significantly enhances its expression under high-temperature conditions. This mechanism provides new insights into understanding how apple responds to high-temperature stress. Additionally, we identified the bHLH transcription factor MdPIF4-Like3 in apple as an interactor of MdGATA15, which stabilizes and enhances the transcriptional activity of MdGATA15, thereby further reinforcing the inhibition of anthocyanin biosynthesis. These findings highlight the central role of MdGATA15 in high-temperature-mediated suppression of anthocyanin synthesis in apple and provide significant advances in understanding the molecular mechanisms of apple's response to heat stress. This study provides a theoretical basis for breeding heat-resistant apple cultivars with improved fruit quality by targeting key transcription factors involved in high-temperature stress response.

Anthocyanins

MhSHINE2-like interacts with MhGRF3 to promote drought tolerance via modulating stomatal aperture in apple.

Drought poses a significant global challenge to agriculture, substantially reducing crop yields. Abscisic acid (ABA) plays a crucial role in response to drought stress. Nevertheless, the molecular mechanism underlying the ABA-mediated drought stress response in apple remains poorly understood. We identified a drought- and ABA-induced AP2/ERF transcription factor (TF), MhSHINE2-like, which positively regulates drought stress tolerance in apple. Biochemical analysis showed that MhSHINE2-like directly binds to the GAGA-rich element in the promoter of the ABA biosynthesis gene MhNCED3, promoting its transcription under drought stress. Overexpression of MhNCED3 promotes ABA accumulation and enhances apple drought tolerance by regulating stomatal closure under drought stress. Further studies revealed that MhSHINE2-like physically interacts with 14-3-3 protein, MhGRF3, which also contributes positively to drought tolerance. Notably, MhSHINE2-like and MhGRF3 function cooperatively to modulate the expression of downstream genes, promoting ABA accumulation, and consequently enhancing drought tolerance in apple. These findings reveal a regulatory network mediated by the combined effects of TFs and chaperone proteins, offering valuable genetic resources for the development of drought-tolerant apple cultivars.

Malus

Molecular Evolution and Expression Analysis of the ADH Gene Family in Apple Bud Mutants.

Alcohol dehydrogenase (ADH) catalyzes the reduction of aldehydes to alcohols, key precursor substrates for volatile ester biosynthesis, which determines the characteristic aroma of apple fruit. However, a comprehensive genome-wide investigation of the ADH gene family in apple has been lacking. In this study, we systematically identified ADH genes in the apple genome using integrated bioinformatics approaches, including phylogenetic analysis, synteny evaluation, promoter cis-element prediction, codon usage bias assessment, and protein interaction network modeling. Expression patterns were examined through transcriptomic data and validated by RT-qPCR analysis across different organs and among 'Red Delicious' and its four bud mutant lines. We identified 44 ADH genes, with 12 forming a prominent cluster on chromosome 1. RT-qPCR analysis revealed that MdADH20 was dramatically upregulated in the 'Red Chief' mutant (relative expression of 59.38), suggesting its pivotal role. Phylogenetic analysis revealed a close evolutionary relationship with wild strawberry. The encoded proteins were generally stable and predominantly localized to the cytoplasm. Promoter analysis showed enrichment of growth/development-related and ARE elements, while codon usage analysis identified AGA, GCU, GUU, and CUU as preferred codons. Protein interaction prediction suggested MdADH19 and MdADH20 as hub proteins. Expression profiling and RT-qPCR further identified MdADH20 as a core candidate gene, characterized by its stable and high expression, particularly in the 'Red Delicious' mutant. Its central position in the predicted protein-protein interaction network suggests a potential regulatory role in the aroma biosynthesis pathway of apple fruit. This study provides the first systematic genome-wide characterization of the apple ADH gene family, establishing a theoretical groundwork for deciphering aroma biosynthesis mechanisms and offering potential target genes for flavor improvement through bud mutation breeding strategies.

ADH gene family

Effects of apple phenolics on the human metabolome: modulation of key metabolic pathways.

Apples are widely recognized for their potential health benefits, partly attributed to their phenolic compounds. However, their impact on human metabolism remains incompletely understood. This study investigated metabolic effects of apple-derived phenolic compounds using untargeted metabolomics approach across multiple biofluids. In a crossover intervention study, 30 healthy men consumed a phenolic-rich apple juice or a placebo for two weeks. Blood, urine and saliva samples were collected before and after each intervention and analyzed by direct infusion ultra-high resolution mass spectrometry. Consumption of apple phenolic compounds resulted in significant alterations of the human metabolome, including increased levels of phenolic-derived degradation products and microbial-associated metabolites across all biofluids. Pathway enrichment analysis revealed pronounced effects on phenylalanine and tyrosine metabolism, as well as linoleic and arachidonic acid metabolism, Overall, these findings demonstrate that apple phenolic compounds induce measurable, microbiota-associated and systemic metabolic changes, providing new insights into their metabolic fate and biological relevance.

Humans

Transcriptional landscape and dynamics involved in sugar and acid accumulation during apple fruit development.

In fleshy fruit, sugars and acids are central components of fruit flavor and quality. To date, the mechanisms underlying transcriptional regulation of sugar and acid during fruit development remain largely unknown. Here, we combined ATAC-seq with RNA-seq to investigate the genome-wide chromatin accessibility and to identify putative transcription factors related to sugar and acid accumulation during apple (Malus domestica) fruit development. By integrating the differentially accessible regions and differentially expressed genes, we generated a global data set of promoter-accessibility and expression-increased genes. Using this strategy, we constructed a transcriptional regulatory network enabling screening for key transcription factors and target genes involved in sugar and acid accumulation. Among these transcription factors, 5 fruit-specific DNA binding with one finger genes were selected to confirm their regulatory effects, and our results showed that they could affect sugar or acid concentration by regulating the expression of sugar or acid metabolism-related genes in apple fruits. Our transcriptional regulatory network provides a suitable platform to identify candidate genes that control sugar and acid accumulation. Meanwhile, our data set will aid in analyzing other characteristics of apple fruit that have not been illuminated previously. Overall, these findings support a better understanding of the regulatory dynamics during apple fruit development and lay a foundation for quality improvement of apple.

Malus

Genome-wide association study combined with multi-assay phenotyping identifies a novel anthracnose resistance locus in apple.

BACKGROUND: Apple anthracnose, a disease complex that includes Glomerella leaf spot (GLS) and bitter rot caused by Colletotrichum species, is a major disease affecting apple production worldwide. In this study, we combined multi-year field evaluations with controlled inoculation assays to identify genomic regions associated with anthracnose resistance in apple. RESULTS: A total of 440 apple genotypes, including 411 F₁ progenies derived from six parental crosses and 29 cultivars, were evaluated under natural orchard conditions and through artificial fruit and leaf inoculation assays using wound and non-wound methods. Disease severity varied substantially between years, particularly under contrasting environmental conditions, indicating strong genotype-by-environment interactions. Genome-wide association analysis (GWAS) using field-derived disease severity scores from 2019 identified a significant quantitative trait locus (QTL) on chromosome 15 (~ 31.8 Mb) associated with reduced anthracnose severity. This locus was distinct from the previously reported Rgls/MdTNL1 region on chromosome 15 (~ 2-5 Mb), suggesting the presence of a novel resistance-associated locus. In contrast, no genome-wide significant associations were detected from artificial inoculation datasets. CONCLUSIONS: These findings demonstrate the importance of field-based, multi-environment phenotyping for detecting field-relevant resistance loci and improving understanding of the genetic architecture underlying anthracnose resistance in apple.

Malus

Genome-Wide Characterization of the Apple HD-Zip IV Gene Family and Functional Validation of MdHDZIV3 Under PEG-Induced Osmotic Stress.

The homeodomain-leucine zipper IV (HD-Zip IV) transcription factor subfamily plays essential roles in epidermal development, cuticle formation, lipid metabolism, and environmental adaptation in plants. Despite its biological importance, the HD-Zip IV family has not been systematically characterized in apple (Malus domestica). Here, we identified 17 apple HD-Zip IV genes and named them MdHDZIV1-MdHDZIV17 based on their locations on the chromosomes. The 17 genes showed a nonuniform distribution on eight chromosomes, while the occurrence of both tandem and segmental duplications indicated that family expansion involved more than one duplication mechanism. All MdHDZIV proteins contained the conserved HD, LZ, START, and SAD domains but lacked the MEKHLA domain, consistent with typical HD-Zip IV structural features. Phylogenetic analysis classified MdHDZIV proteins into five groups together with HD-Zip IV members from Arabidopsis thaliana and rice, indicating evolutionary conservation of this subfamily. Collinearity and Ka/Ks analyses revealed that duplicated MdHDZIV gene pairs were mainly subjected to purifying selection. Promoter scanning revealed diverse cis-regulatory motifs associated with hormonal signaling, environmental stress, light response, and epidermal regulation, including ABRE, ARE, W-box, MYC, G-box, and L1-box motifs. Integration of transcriptomic profiling with qRT-PCR validation revealed pronounced tissue-dependent differences in the expression of MdHDZIV genes in leaf, fruit skin, and branch bark. Under PEG6000-induced osmotic stress and NaCl-induced salt stress, 10 candidate MdHDZIV genes displayed gene-specific and stress type-specific expression patterns, with MdHDZIV3 showing strong induction under PEG6000 treatment. Functional validation in apple calli showed that MdHDZIV3 overexpression enhanced PEG tolerance, increased fresh weight, elevated SOD and POD activities, and reduced MDA accumulation under osmotic stress. These findings provide a genome-wide framework for understanding the apple HD-Zip IV gene family.

abiotic stress

MdWRKY75 interacts with MdWOX11 to modulate root growth under salt stress in apple.

The root system is pivotal for plant development, enabling both vegetative growth and tolerance to abiotic stresses like salinity. However, the molecular mechanisms governing root adaptive development in response to salt stress remain poorly understood in apple (Malus domestica Borkh.). In this study, we identified the salt stress-responsive WRKY transcription factor MdWRKY75. Overexpression of MdWRKY75 in transgenic apple negatively regulates adventitious root (AR) formation and salt stress tolerance, whereas reducing MdWRKY75 expression yields the opposite phenotype. Moreover, MdWRKY75 directly binds to the promoter of MdSAUR15 (SMALL AUXIN UP RNA15) and transcriptionally represses the expression of MdSAUR15, which, when overexpressed, promotes AR formation and enhances salt stress tolerance. We further demonstrated that MdWRKY75 interacts with MdWOX11, a WUSCHEL-related homeobox (WOX) transcription factor, both in vitro and in vivo. MdWOX11 expression is upregulated and enhances AR formation under salt stress. Additionally, MdWOX11 reduces the binding of MdWRKY75 to the MdSAUR15 promoter, and alleviates the MdWRKY75-mediated inhibitory effect on MdSAUR15 expression. Collectively, our study provides a MdWOX11-MdWRKY75-MdSAUR15 module regulating root adaptation in response to salt stress in apple.

Malus

Characterization and genomic analysis of Bacillus halotolerans G3-2: a potential biocontrol agent against apple Alternaria leaf blotch disease.

BACKGROUND: Apple Alternaria leaf blotch (ALB) is a devastating disease threatening the apple industry worldwide. Biocontrol offers an effective and environmentally friendly alternative for disease management. RESULTS: Bacillus strain G3-2 exhibits strong antagonistic activity against Alternaria alternata (a major causal pathogen of ALB). In dual-culture assays, G3-2 inhibited A. alternata by 88.39%; in detached-leaf inoculation assays, it reduced the lesion area by >88%. 16S rRNA sequencing and phylogenetic analysis identified this strain as Bacillus halotolerans. Oxford Nanopore Technology (ONT) sequencing generated a 4.18-Mb complete genome (43.8% G + C) containing 4149 protein-coding genes, 30 rRNAs and 86 tRNAs. CAZy annotation identified 182 genes encoding carbohydrate-active enzymes (CAZymes), including glycoside hydrolases, glycosyltransferase, and carbohydrate esterases, suggesting potential for glycosylated secondary metabolite production. AntiSMASH analysis detected nine biosynthetic gene clusters, including those for surfactin, fengycin, bacillaene and laterocidine. Plate assays confirmed that G3-2 has the ability to produce protease, cellulase and siderophore. Moreover, it exhibits ~70% inhibition against several other phytopathogenic fungi. CONCLUSIONS: These findings demonstrate that G3-2 suppresses A. alternata through antibiosis (lipopeptides and polyketides), nutrient competition (siderophores) and cell-wall degradation (proteases and cellulases). Moreover, our study revealed that it has great potential to be used as a broad-spectrum, environmentally friendly biocontrol agent. © 2026 Society of Chemical Industry.

Alternaria

Functional characterization of the MdFLZ2 gene in drought and salt stress tolerance in apple.

Drought and salt stress are significant environmental limitations that severely constrain plant growth and productivity, therefore, enhancing stress tolerance is a key goal in crop improvement. The plant-specific FCS-like zinc finger (FLZ) proteins have been identified as important regulators of stress adaptation. In this study, we conducted a genome-wide characterization of the FLZ gene family in apple and functionally characterized MdFLZ2. qRT-PCR analysis revealed that MdFLZ2 was differentially expressed across various tissues and transcriptionally induced by both drought and salt stress. Subcellular localization assays demonstrated that the MdFLZ2 protein is localized to both the nucleus and the cytoplasm. The overexpression of MdFLZ2 in apple calli, Arabidopsis and tomato conferred increased resistance to drought and salt stress. In addition, yeast two-hybrid (Y2H) assays confirmed that MdFLZ2 interacted with MdSnRK1.1, and similar interactions were also detected between other MdFLZ family members and MdSnRK1.1. Collectively, our findings suggest MdFLZ2 as a positive regulator of drought and salt tolerance and highlight its potential to serve as a genetic resource for abiotic stress improvement.

Malus

A high-quality chromosome-level genome assembly of apple of Peru (Nicandra physalodes).

Nicandra physalodes, a member of the Solanaceae family, is known for its medicinal potential and strong natural insect-repellent properties, which are mainly attributed to its bioactive withanolides and alkaloids. Despite its ecological and pharmacological significance, genomic information for this species has remained limited. Here, we generated a chromosome-level reference genome for N. physalodes based on PacBio high-fidelity (HiFi) long-read sequencing and Hi-C scaffolding. The assembled genome is 933.97 Mb in size, with a contig N50 of 87.37 Mb, and 99.95% (933.54 Mb) of the sequences anchored to 10 pseudochromosomes. Repetitive elements account for 73.06% of the genome, and 27,925 protein-coding genes were predicted, 97.81% of which were functionally annotated. This genomic resource provides a valuable foundation for investigating the genetic basis of specialized metabolite biosynthesis, insect resistance, and environmental adaptation in N. physalodes, as well as for comparative studies within the Solanaceae family.

Genome, Plant

Genome-wide identification of potassium transporters and channels in Malus domestica genome.

Potassium (K+) is an essential nutrient for plants. It contributes to most physiological and biochemical pathways for plant metabolism, growth, and development. It is the most available plant nutrient, comprising 10–15% of plant weight. Plants have a sophisticated system of K+ transporters and channels for distribution in plant body. Apple is one of the most consumed fruits in the world. Its fruit quality and yield are positively affected by K+. However, limited information is available about K+ transport systems in Apple. In this study, 47 candidate genes (26 K+ transporters and 21 K+ channels) have been identified in Apple (Malus domestica) genome. The phylogenetic comparisons with other plants (Glycine max, Arabidopsis thaliana, and Oryza sativa) indicated that the K+ transport system is much conserved among different plants. The analysis of Gene structure showed the presence of specific introns and exon patterns for these gene families. Transcriptomic data analysis and RT-qPCR demonstrated significant variations in the transcript abundance of these genes in response to abiotic stresses. The current project represents the first report about the K+ transport system in Apple. Therefore, it may act as a starting point for further functional characterizations.

Malus

Evaluating Wearable Devices for Remote Monitoring in Psychosis: Pilot Study Nested Within the CONNECT Cohort Study.

BACKGROUND: Digital remote monitoring technologies, including smartphones and wearables, offer promising avenues for early detection of psychosis relapse. However, selecting devices that are acceptable to participants and produce high-quality data remains challenging. OBJECTIVE: The aim of this nested pilot study was to assess the acceptability and data quality of 3 commercially available wearable devices in people with psychosis recruited to the CONNECT cohort study. METHODS: Participants recruited to the CONNECT study before July 31, 2024, were included in the pilot study and selected 1 of 3 wearable devices: a Fitbit Charge 5, Samsung Galaxy Watch 5, or Apple Watch SE. Baseline demographics were compared between device groups. Acceptability of devices to participants was assessed through a Wearable Device Satisfaction Questionnaire after 3 months of use, with the proportion of positive responses to each question calculated and compared. Data completeness was also assessed by calculating the number (and percentage) of valid days of step count, heart rate, and sleep data, and comparing between groups. Data quality was assessed through summarizing the amount of troubleshooting required, additional metrics available from the wearables, and continuity of data completeness by calculating the proportion of participants with at least 3 days of heart rate data per week for the first 20 weeks of follow-up. Predefined criteria were used to determine the next steps for the wider CONNECT study: if one device was superior, this would be selected; if none were found to be superior and the Fitbit was found to be noninferior, then Fitbit would be retained. RESULTS: Of the first 107 participants recruited to CONNECT, 105 were included in the pilot study evaluation. The Samsung Galaxy Watch was selected most frequently by participants (46/105, 43.8%), followed by the Apple Watch (27/105, 25.7%), and Fitbit Charge (23/105, 21.9%). Differences in participant demographics were observed across device groups. Self-reported acceptability after use did not differ substantially between devices. However, in terms of data completeness, the median proportion of valid heart rate data days was significantly lower for Samsung Galaxy (median 31.2%, IQR 8.5%-46.0%) compared to Fitbit (median 80.1%, IQR 26.7%-95.0%; P=.003) and Apple Watch (median 49.3%, IQR 21.5%-86.0%; P=.02). There was no significant difference between Fitbit and Apple Watch. Similar patterns were observed for step count and sleep data. The Samsung Galaxy Watch required more frequent troubleshooting for data flow issues and lacked additional physiological metrics, available from the other devices. CONCLUSIONS: Due to comparatively lower data quality and technical performance, the Samsung Galaxy Watch was discontinued for use in the subsequent phase of the CONNECT study. The study highlights the importance of incorporating nested evaluations of devices in long-term research.

Humans