Molecular evolution of Phytocyanin gene and analysis of expression at different coloring periods in apple (Malus domestica).

BACKGROUND: PC (phytocyanin) is a class of copper-containing electron transfer proteins closely related to plant photosynthesis, abiotic stress responses growth and development in plants, and regulation of the expression of some flavonoids and phenylpropanoids, etc., however, compared with other plants, the PC gene family has not been systematically characterized in apple. RESULTS: A total of 59 MdPC gene members unevenly distributed across 12 chromosomes were identified at the genome-wide level. The proteins of the MdPC family were classified into four subfamilies based on differences in copper binding sites and glycosylation sites: Apple Early nodulin-like proteins (MdENODLs), Apple Uclacyanin-like proteins (MdUCLs), Apple Stellacyanin-like proteins (MdSCLs), and Apple Plantacyanin-like proteins (MdPLCLs). Some MdPC members with similar gene structures and conserved motifs belong to the same group or subfamily. The internal collinearity analysis revealed 14 collinearity gene pairs among members of the apple MdPC gene. Interspecific collinearity analysis showed that apple had 31 and 35 homologous gene pairs with strawberry and grape, respectively. Selection pressure analysis indicated that the MdPC gene was under purifying selection. Prediction of protein interactions showed that MdPC family members interacted strongly with the Nad3 protein. GO annotation results indicated that the MdPC gene also regulated the biosynthesis of phenylpropanoids. Chip data analysis showed that (MdSCL3, MdSCL7 and MdENODL27) were highly expressed in mature fruits and peels. Many cis-regulatory elements related to light response, phytohormones, abiotic stresses and flavonoid biosynthetic genes regulation were identified 2000 bp upstream of the promoter of the MdPC gene, and qRT-PCR results showed that gene members in Group IV (MdSCL1/3, MdENODL27) were up-regulated at all five stages of apple coloring, but the highest expression was observed at the DAF13 (day after fruit bag removal) stage. The gene members in Group II (MdUCL9, MdPLCL3) showed down-regulated or lower expression in the first four stages of apple coloring but up-regulated and highest expression in the DAF 21 stage. CONCLUSION: Herein, one objective of these findings is to provide valuable information for understanding the structure, molecular evolution, and expression pattern of the MdPC gene, another major objective in this study was designed to lay the groundwork for further research on the molecular mechanism of PC gene regulation of apple fruit coloration.

Identification of Hsp20 gene family in Malus domestica and functional characterization of Hsp20 class I gene MdHsp18.2b.

Heat shock protein 20 (Hsp20) is a small molecule heat shock protein that plays an important role in plant growth, development, and stress resistance. Little is known about the function of Hsp20 family genes in apple (Malus domestica). Here, we performed a genome-wide analysis of the apple Hsp20 gene family, and a total of 49 Hsp20s genes were identified from the apple genome. Phylogenetic analysis revealed that the 49 genes were divided into 11 subfamilies, and MdHsp18.2b, a member located in the CI branch, was selected as a representative member for functional characterization. Treatment with NaCl and Botryosphaeria dothidea (B. dothidea), the causal agent of apple ring rot disease, significantly induced MdHsp18.2b transcription level. Further analysis revealed that overexpressing MdHsp18.2b reduced the resistance to salt stress but enhanced the resistance to B. dothidea infection in apple calli. Moreover, MdHsp18.2b positively regulated anthocyanin accumulation in apple calli. Physiology assays revealed that MdHsp18.2b promoted H2O2 production, even in the absence of stress factors, which might contribute to its functions in response to NaCl and B. dothidea infection. Hsps usually function as homo- or heterooligomers, and we found that MdHsp18.2b could form a heterodimer with MdHsp17.9a and MdHsp17.5, two members from the same branch with MdHsp18.2b in the phylogenetic tree. Therefore, we identified 49 Hsp20s genes from the apple genome and found that MdHsp18.2b was involved in regulating plant resistance to salt stress and B. dothidea infection, as well as in regulating anthocyanin accumulation in apple calli.

Molecular Mechanism of Resistance to Alternaria alternata Apple Pathotype in Apple by Alternative Splicing of Transcription Factor MdMYB6-like.

As a fruit tree with great economic value, apple is widely cultivated in China. However, apple leaf spot disease causes significant damage to apple quality and economic value. In our study, we found that MdMYB6-like is a transcription factor without auto-activation activity and with three alternative spliced variants. Among them, MdMYB6-like-ß responded positively to the pathogen infection. Overexpression of MdMYB6-like-ß increased the lignin content of leaves and improved the pathogenic resistance of apple flesh callus. In addition, all three alternative spliced variants of MdMYB6-like could bind to the promoter of MdBGLU H. Therefore, we believe that MdMYB6-like plays an important role in the infection process of the pathogen and lays a solid foundation for breeding disease-resistant cultivars of apple in the future.

Epigenomic mechanism regulating the quality and ripeness of apple fruit with differing harvest maturity.

Harvest maturity significantly affects the quality of apple fruit in post-harvest storage process. Although the regulatory mechanisms underlying fruit ripening have been studied, the associated epigenetic modifications remain unclear. Thus, we compared the DNA methylation changes and the transcriptional responses of mature fruit (MF) and immature fruit (NF). There were significant correlations between DNA methylation and gene expression. Moreover, the sugar contents (sucrose, glucose, and fructose) were higher in MF than in NF, whereas the opposite pattern was detected for the starch content. The expression-level differences were due to DNA methylations and ultimately resulted in diverse fruit textures and ripeness. Furthermore, the higher ethylene, auxin, and abscisic acid levels in MF than in NF, which influenced the fruit texture and ripening, were associated with multiple differentially expressed genes in hormone synthesis, signaling, and response pathways (ACS, ACO, ZEP, NCED, and ABA2) that were regulated by DNA methylations. Multiple transcription factor genes involved in regulating fruit ripening and quality via changes in DNA methylation were identified, including MIKCC-type MADS-box genes and fruit ripening-related genes (NAP, SPL, WRKY, and NAC genes). These findings reflect the diversity in the epigenetic regulation of gene expression and may be relevant for elucidating the epigenetic regulatory mechanism underlying the ripening and quality of apple fruit with differing harvest maturity.

[In silico analysis of Cit s 2: A highly conserved profilin]. / Análisis in silico de cit s 2: una profilina altamente conservada.

OBJECTIVE: Analyze phylogenetic relationships and molecular mimicry of Cit s 2 and other plant profilins. METHODS: Online bioinformatics tools including Basic Local Alignment Search Tool (BLASTP), PRALINE and MEGA were used for multiple alignments and phylogenetic analysis. A 3D-homology model of Cit s 2 was predicted. Models were calculated with MODELLER. The best model was selected with the model scoring option of MAESTRO. Conserved regions between Cit s 2 and other profilins were located on the 3D model and antigenic regions were predicted by ElliPro server (3-5). RESULTS: Cit s 2 amino acid sequence (Uniprot code:P84177) was compared with other 30 profilins from different allergenic sources. The identity between Cit s 2 and other profilins ranged between 82 and 99%. The highest identity was observed with Cucumis melo (99%) followed by Prunus persica (98%) and Malus domestica (92%). High conserved antigenic regions were observed on the 3D predicted model. Seven lineal and six discontinuous epitopes were found in Cit s 2. CONCLUSION: High conserved antigenic regions were observed on the 3D predicted model of Cit s 2, which might involve potential cross-reactivity between Cit s 2 and other profilins. Future studies are needed to further analyze these results.

OBJETIVO: Analizar las relaciones filogenéticas y el mimetismo molecular de Cit s 2 y otras profilinas vegetales. MÉTODOS: Se utilizaron herramientas bioinformáticas en línea, incluida la de búsqueda de alineación local básica (BLASTP), PRALINE y MEGA, para alineamientos múltiples y análisis filogenético. Se predijo un modelo de homología 3D de Cit s 2. Los modelos se calcularon con MODELLER. El mejor modelo fue seleccionado con la opción de puntuación de modelo de Maestro. Las regiones conservadas entre Cit s 2 y otras profilinas se ubicaron en el modelo 3D y las regiones antigénicas fueron predichas por el servidor ElliPro (3-5). RESULTADOS: La secuencia de aminoácidos de Cit s 2 (código Uniprot: P84177), se comparó con otras 30 profilinas de diferentes fuentes alergénicas. La mayor identidad se observó con Cucumis melo (99%) seguida de Prunus persica (98%) y Malus domestica (92%). Se observaron regiones antigénicas altamente conservadas en el modelo predicho en 3D. Se encontraron siete epítopes lineales, y seis epítopes discontinuos en Cit s 2. CONCLUSIÓN: Se observaron regiones antigénicas altamente conservadas en el modelo 3D predicho de Cit s 2, lo que podría implicar una posible reactividad cruzada entre Cit s 2 y otras profilinas. Se necesitan estudios futuros para analizar más a fondo estos resultados.

MdTPR16, an apple tetratricopeptide repeat (TPR)-like superfamily gene, positively regulates drought stress in apple.

The Tetratricopeptide repeat (TPR)-like superfamily with TPR conserved domains is widely involved in the growth and abiotic stress in many plants. In this report, the gene MdTPR16 belongs to the TPR family in apple (Malus domestica). Promoter analysis reveal that MdTPR16 incorporated various stress response elements, including the drought stress response elements. And different abiotic stress treatments, drought especially, significantly induce the response of MdTPR16. Overexpression of MdTPR16 result in better drought tolerance in apple and Arabidopsis by up-regulating the expression levels of drought stress-related genes, achieving a higher chlorophyll content level, more material accumulation, and overall better growth compared to WT in the drought. Under drought stress, the overexpressed MdTPR16 also mitigate the oxidative damage in cells by reducing the electrolyte leakage, malondialdehyde content, and the H2O2 and O2- accumulation in apples and Arabidopsis. In conclusion, MdTPR16 act as a beneficial regulator of drought stress response by regulating the expression of related genes and the cumulation of reactive oxygen species (ROS).

Transcriptomic investigation of the interaction between a biocontrol yeast, Papiliotrema terrestris strain PT22AV, and the postharvest fungal pathogen Penicillium expansum on apple.

Biocontrol strategies offer a promising alternative to control plant pathogens achieving food safety and security. In this study we apply a RNAseq analysis during interaction between the biocontrol agent (BCA) Papiliotrema terrestris, the pathogen Penicillium expansum, and the host Malus domestica. Analysis of the BCA finds overall 802 upregulated DEGs (differentially expressed genes) when grown in apple tissue, with the majority being involved in nutrients uptake and oxidative stress response. This suggests that these processes are crucial for the BCA to colonize the fruit wounds and outcompete the pathogen. As to P. expansum analysis, 1017 DEGs are upregulated when grown in apple tissue, with the most represented GO categories being transcription, oxidation reduction process, and transmembrane transport. Analysis of the host M. domestica finds a higher number of DEGs in response to the pathogen compared to the BCA, with overexpression of genes involved in host defense signaling pathways in the presence of both of them, and a prevalence of pattern-triggered immunity (PTI) and effector-triggered immunity (ETI) only during interaction with P. expansum. This analysis contributes to advance the knowledge on the molecular mechanisms that underlie biocontrol activity and the tritrophic interaction of the BCA with the pathogen and the host.

MdPRX34L, a class III peroxidase gene, activates the immune response in apple to the fungal pathogen Botryosphaeria dothidea.

MAIN CONCLUSION: MdPRX34L enhanced resistance to Botryosphaeria dothidea by increasing salicylic acid (SA) and abscisic acid (ABA) content as well as the expression of related defense genes. The class III peroxidase (PRX) multigene family is involved in complex biological processes. However, the molecular mechanism of PRXs in the pathogen defense of plants against Botryosphaeria dothidea (B. dothidea) remains unclear. Here, we cloned the PRX gene MdPRX34L, which was identified as a positive regulator of the defense response to B. dothidea, from the apple cultivar 'Royal Gala.' Overexpression of MdPRX34L in apple calli decreased sensitivity to salicylic acid (SA) and abscisic acid（ABA). Subsequently, overexpression of MdPRX34L in apple calli increased resistance to B. dothidea infection. In addition, SA contents and the expression levels of genes related to SA synthesis and signaling in apple calli overexpressing MdPRX34L were higher than those in the control after inoculation, suggesting that MdPRX34L enhances resistance to B. dothidea via the SA pathway. Interestingly, infections in apple calli by B. dothidea caused an increase in endogenous levels of ABA followed by induction of ABA-related genes expression. These findings suggest a potential mechanism by which MdPRX34L enhances plant-pathogen defense against B. dothidea by regulating the SA and ABA pathways.

Multi-omics analysis reveals the biosynthesis of flavonoids during the browning process of Malus sieversii explants.

Malus sieversii is a precious apple germplasm resource. Browning of explants is one of the most important factors limiting the survival rate of plant tissue culture. In order to explore the molecular mechanism of the browning degree of different strains of Malus sieversii, we compared the dynamic changes of Malus sieversii and Malus robusta Rehd. during the whole browning process using a multi-group method. A total of 44 048 differentially expressed genes (DEGs) were identified by transcriptome analysis on the DNBSEQ-T7 sequencing platform. KEGG enrichment analysis showed that the DEGs were significantly enriched in the flavonoid biosynthesis pathway. In addition, metabonomic analysis showed that (-)-epicatechin, astragalin, chrysin, irigenin, isoquercitrin, naringenin, neobavaisoflavone and prunin exhibited different degrees of free radical scavenging ability in the tissue culture browning process, and their accumulation in different varieties led to differences in the browning degree among varieties. Comprehensive transcriptome and metabonomics analysis of the data related to flavonoid biosynthesis showed that PAL, 4CL, F3H, CYP73A, CHS, CHI, ANS, DFR and PGT1 were the key genes for flavonoid accumulation during browning. In addition, WGCNA analysis revealed a strong correlation between the known flavonoid structure genes and the selected transcriptional genes. Protein interaction predictions demonstrated that 19 transcription factors (7 MYBs and 12 bHLHs) and 8 flavonoid structural genes had targeted relationships. The results show that the interspecific differential expression of flavonoid genes is the key influencing factor of the difference in browning degree between Malus sieversii and Malus robusta Rehd., providing a theoretical basis for further study on the regulation of flavonoid biosynthesis.

Identification of a negative-strand RNA virus with natural plant and fungal hosts.

The presence of viruses that spread to both plant and fungal populations in nature has posed intriguingly scientific question. We found a negative-strand RNA virus related to members of the family Phenuiviridae, named Valsa mali negative-strand RNA virus 1 (VmNSRV1), which induced strong hypovirulence and was prevalent in a population of the phytopathogenic fungus of apple Valsa canker (Valsa mali) infecting apple orchards in the Shaanxi Province of China. Intriguingly, VmNSRV1 encodes a protein with a viral cell-to-cell movement function in plant tissue. Mechanical leaf inoculation showed that VmNSRV1 could systemically infect plants. Moreover, VmNSRV1 was detected in 24 out of 139 apple trees tested in orchards in Shaanxi Province. Fungal inoculation experiments showed that VmNSRV1 could be bidirectionally transmitted between apple plants and V. mali, and VmNSRV1 infection in plants reduced the development of fungal lesions on leaves. Additionally, the nucleocapsid protein encoded by VmNSRV1 is associated with and rearranged lipid droplets in both fungal and plant cells. VmNSRV1 represents a virus that has adapted and spread to both plant and fungal hosts and shuttles between these two organisms in nature (phyto-mycovirus) and is potential to be utilized for the biocontrol method against plant fungal diseases. This finding presents further insights into the virus evolution and adaptation encompassing both plant and fungal hosts.

Identification of two key genes involved in flavonoid catabolism and their different roles in apple resistance to biotic stresses.

Biosynthesis of flavonoid aglycones and glycosides is well established. However, key genes involved in their catabolism are poorly understood, even though the products of hydrolysis and oxidation play important roles in plant resistance to biotic stress. Here, we report on catabolism of dihydrochalcones (DHCs), the most abundant flavonoids in domesticated apple and wild Malus. Two key genes, BGLU13.1 and PPO05, were identified by activity-directed protein purification. BGLU13.1-A hydrolyzed phlorizin, (the most abundant DHC in domesticated apple) to produce phloretin which was then oxidized by PPO05. The process differed in some wild Malus, where trilobatin (a positional isomer of phlorizin) was mainly oxidized by PPO05. The effects of DHC catabolism on apple resistance to biotic stresses was investigated using transgenic plants. Either directly or indirectly, phlorizin hydrolysis affected resistance to the phytophagous pest two-spotted spider mite, while oxidation of trilobatin was involved in resistance to the biotrophic fungus Podosphaera leucotricha. DHC catabolism did not affect apple resistance to necrotrophic pathogens Valsa mali and Erwinia amylovara. These results suggest that different DHC catabolism pathways play different roles in apple resistance to biotic stresses. The role of DHC catabolism on apple resistance appeared closely related to the mode of invasion/damage used by pathogen/pest.

miR164-MhNAC1 regulates apple root nitrogen uptake under low nitrogen stress.

Nitrogen is an essential nutrient for plant growth and serves as a signaling molecule to regulate gene expression inducing physiological, growth and developmental responses. An excess or deficiency of nitrogen may have adverse effects on plants. Studying nitrogen uptake will help us understand the molecular mechanisms of utilization for targeted molecular breeding. Here, we identified and functionally validated an NAC (NAM-ATAF1/2-CUC2) transcription factor based on the transcriptomes of two apple rootstocks with different nitrogen uptake efficiency. NAC1, a target gene of miR164, directly regulates the expression of the high-affinity nitrate transporter (MhNRT2.4) and citric acid transporter (MhMATE), affecting root nitrogen uptake. To examine the role of MhNAC1 in nitrogen uptake, we produced transgenic lines that overexpressed or silenced MhNAC1. Silencing MhNAC1 promoted nitrogen uptake and citric acid secretion in roots, and enhanced plant tolerance to low nitrogen conditions, while overexpression of MhNAC1 or silencing miR164 had the opposite effect. This study not only revealed the role of the miR164-MhNAC1 module in nitrogen uptake in apple rootstocks but also confirmed that citric acid secretion in roots affected nitrogen uptake, which provides a research basis for efficient nitrogen utilization and molecular breeding in apple.

The Mh-miR393a-TIR1 module regulates Alternaria alternata resistance of Malus hupehensis mainly by modulating the auxin signaling.

miRNAs govern gene expression and regulate plant defense. Alternaria alternata is a destructive fungal pathogen that damages apple. The wild apple germplasm Malus hupehensis is highly resistant to leaf spot disease caused by this fungus. Herein, we elucidated the regulatory and functional role of miR393a in apple resistance against A. alternata by targeting Transport Inhibitor Response 1. Mature miR393 accumulation in infected M. hupehensis increased owing to the transcriptional activation of MIR393a, determined to be a positive regulator of A. alternata resistance to either 'Orin' calli or 'Gala' leaves. 5' RLM-RACE and co-transformation assays showed that the target of miR393a was MhTIR1, a gene encoding a putative F-box auxin receptor that compromised apple immunity. RNA-seq analysis of transgenic calli revealed that MhTIR1 upregulated auxin signaling gene transcript levels and influenced phytohormone pathways and plant-pathogen interactions. miR393a compromised the sensitivity of several auxin-signaling genes to A. alternata infection, whereas MhTIR1 had the opposite effect. Using exogenous indole-3-acetic acid or the auxin synthesis inhibitor L-AOPP, we clarified that auxin enhances apple susceptibility to this pathogen. miR393a promotes SA biosynthesis and impedes pathogen-triggered ROS bursts by repressing TIR1-mediated auxin signaling. We uncovered the mechanism underlying the miR393a-TIR1 module, which interferes with apple defense against A. alternata by modulating the auxin signaling pathway.

Analysis of flavonoid metabolism of compounds in succulent fruits and leaves of three different colors of Rosaceae.

Red flesh apple (Malus pumila var. medzwetzkyana Dieck), purple leaf plum (Prunus cerasifera Ehrhar f), and purple leaf peach (Prunus persica 'Atropurpurea') are significant ornamental plants within the Rosaceae family. The coloration of their fruits and leaves is crucial in their appearance and nutritional quality. However, qualitative and quantitative studies on flavonoids in the succulent fruits and leaves of multicolored Rosaceae plants are lacking. To unveil the diversity and variety-specificity of flavonoids in these three varieties, we conducted a comparative analysis of flavonoid metabolic components using ultra-high-performance liquid phase mass spectrometry (UPLC-MS/MS). The results revealed the detection of 311 metabolites, including 47 flavonoids, 105 flavonols, 16 chalcones, 37 dihydroflavonoids, 8 dihydroflavonols, 30 anthocyanins, 14 flavonoid carbon glycosides, 23 flavanols, 8 isoflavones, 11 tannins, and 12 proanthocyanidins. Notably, although the purple plum and peach leaves exhibited distinct anthocyanin compounds, paeoniflorin and corythrin glycosides were common but displayed varying glycosylation levels. While the green purple leaf peach fruit (PEF) and red flesh apple leaf (AL) possessed the lowest anthocyanin content, they exhibited the highest total flavonoid content. Conversely, the red flesh apple fruit (AF) displayed the highest anthocyanin content and a diverse range of anthocyanin glycosylation modifications, indicating that anthocyanins predominantly influenced the fruit's color. Purple PLF, PLL, and PEL showcased varying concentrations of anthocyanins, suggesting that their colors result from the co-color interaction between specific types of anthocyanins and secondary metabolites, such as flavonols, flavonoids, and dihydroflavonoids. This study provides novel insights into the variations in tissue metabolites among Rosaceae plants with distinct fruit and leaf colors.

FLOWERING LOCUS T1 and TERMINAL FLOWER1 regulatory networks mediate flowering initiation in apple.

Flower bud formation is a critical process that directly determines yield and fruit quality in fruit crops. Floral induction is modulated by the balance between 2 flowering-related proteins, FLOWERING LOCUS T (FT) and TERMINAL FLOWER1 (TFL1); however, the mechanisms underlying the establishment and maintenance of this dynamic balance remain largely elusive. Here, we showed that in apple (Malus × domestica Borkh.), MdFT1 is predominantly expressed in spur buds and exhibits an increase in expression coinciding with flower induction; in contrast, MdTFL1 exhibited downregulation in apices during flower induction, suggesting that MdTFL1 has a role in floral repression. Interestingly, both the MdFT1 and MdTFL1 transcripts are directly regulated by transcription factor basic HELIX-LOOP-HELIX48 (MdbHLH48), and overexpression of MdbHLH48 in Arabidopsis (Arabidopsis thaliana) and tomato (Solanum lycopersicum) results in accelerated flowering. Binding and activation analyses revealed that MdbHLH48 functions as a positive regulator of MdFT1 and a negative regulator of MdTFL1. Further studies established that both MdFT1 and MdTFL1 interact competitively with MdWRKY6 protein to facilitate and inhibit, respectively, MdWRKY6-mediated transcriptional activation of target gene APPLE FLORICAULA/LFY (AFL1, an apple LEAFY-like gene), ultimately regulating apple flower bud formation. These findings illustrate the fine-tuned regulation of flowering by the MdbHLH48-MdFT1/MdTFL1-MdWRKY6 module and provide insights into flower bud formation in apples.

Link between organic nanovescicles from vegetable kingdom and human cell physiology: intracellular calcium signalling.

BACKGROUND: Plant-derived nanovesicles (PDNVs) are a novelty in medical and agrifood environments, with several studies exploring their functions and potential applications. Among fruits, apples (sp. Malus domestica) have great potential as PDNVs source, given their widespread consumption, substantial waste production, and recognized health benefits. Notably, apple-derived nanovesicles (ADNVs) can interact with human cell lines, triggering anti-inflammatory and antioxidant responses. This work is dedicated to the comprehensive biochemical characterization of apple-derived nanovesicles (ADNVs) through proteomic and lipidomic analysis, and small RNAs sequencing. This research also aims to shed light on the underlying mechanism of action (MOA) when ADNVs interface with human cells, through observation of intracellular calcium signalling in human fibroblasts, and to tackles differences in ADNVs content when isolated from fruits derived from integrated and organic production methods cultivars. RESULTS: The ADNVs fraction is mainly composed of exocyst-positive organelles (EXPOs) and MVB-derived exosomes, identified through size and molecular markers (Exo70 and TET-3-like proteins). ADNVs' protein cargo is heterogeneous and exhibits a diverse array of functions, especially in plant's protection (favouring ABA stress-induced signalling, pathogen resistance and Reactive Oxygen Species (ROS) metabolism). Noteworthy plant miRNAs also contribute to phytoprotection. In relation with human cells lines, ADNVs elicit spikes of intracellular Ca2+ levels, utilizing the cation as second messenger, and produce an antioxidant effect. Lastly, organic samples yield a substantial increase in ADNV production and are particularly enriched in bioactive lysophospholipids. CONCLUSIONS: We have conclusively demonstrated that ADNVs confer an antioxidant effect upon human cells, through the initiation of a molecular pathway triggered by Ca2+ signalling. Within ADNVs, a plethora of bioactive proteins, small RNAs, and lipids have been identified, each possessing well-established functions within the realm of plant biology. While ADNVs predominantly function in plants, to safeguard against pathogenic agents and abiotic stressors, it is noteworthy that proteins with antioxidant power might act as antioxidants within human cells.

Transcriptome Analysis of White- and Red-Fleshed Apple Fruits Uncovered Novel Genes Related to the Regulation of Anthocyanin Biosynthesis.

The red flesh coloration of apples is a result of a biochemical pathway involved in the biosynthesis of anthocyanins and anthocyanidins. Based on apple genome analysis, a high number of regulatory genes, mainly transcription factors such as MYB, which are components of regulatory complex MYB-bHLH-WD40, and several structural genes (PAL, 4CL, CHS, CHI, F3H, DFR, ANS, UFGT) involved in anthocyanin biosynthesis, have been identified. In this study, we investigated novel genes related to the red-flesh apple phenotype. These genes could be deemed molecular markers for the early selection of new apple cultivars. Based on a comparative transcriptome analysis of apples with different fruit-flesh coloration, we successfully identified and characterized ten potential genes from the plant hormone transduction pathway of auxin (GH3); cytokinins (B-ARR); gibberellins (DELLA); abscisic acid (SnRK2 and ABF); brassinosteroids (BRI1, BZR1 and TCH4); jasmonic acid (MYC2); and salicylic acid (NPR1). An analysis of expression profiles was performed in immature and ripe fruits of red-fleshed cultivars. We have uncovered genes mediating the regulation of abscisic acid, salicylic acid, cytokinin, and jasmonic acid signaling and described their role in anthocyanin biosynthesis, accumulation, and degradation. The presented results underline the relationship between genes from the hormone signal transduction pathway and UFGT genes, which are directly responsible for anthocyanin color transformation as well as anthocyanin accumulation during apple-fruit ripening.

Valsa mali effector Vm_04797 interacts with adaptor protein MdAP-2ß to manipulate host autophagy.

Apple Valsa canker, caused by the ascomycete fungus Valsa mali, employs virulence effectors to disturb host immunity and poses a substantial threat to the apple industry. However, our understanding of how V. mali effectors regulate host defense responses remains limited. Here, we identified the V. mali effector Vm_04797, which was upregulated during the early infection stage. Vm_04797, a secreted protein, suppressed Inverted formin 1 (INF1)-triggered cell death in Nicotiana benthamiana and performed virulence functions inside plant cells. Vm_04797 deletion mutants showed substantially reduced virulence toward apple. The adaptor protein MdAP-2ß positively regulated apple Valsa canker resistance and was targeted and degraded by Vm_04797 via the ubiquitination pathway. The in vitro analysis suggested that Vm_04797 possesses E3 ubiquitin ligase activity. Further analysis revealed that MdAP-2ß is involved in autophagy by interacting with Malus domestica autophagy protein 16 MdATG16 and promoting its accumulation. By degrading MdAP-2ß, Vm_04797 inhibited autophagic flux, thereby disrupting the defense response mediated by autophagy. Our findings provide insights into the molecular mechanisms employed by the effectors of E3 ubiquitin ligase activity in ascomycete fungi to regulate host immunity.

The apple Ca2+/H+ exchanger MdCAX2L-2 functions positively in modulation of Ba2+ tolerance.

Calcium is an essential element for plant growth and development, and it plays an important role in the responses of plants to abiotic stress. High concentrations of heavy metal ions in soil significantly affect the yield and quality of crops and pose human health threats when these ions accumulate in edible organs. The Ca2+/H+ exchanger (CAX) family is a class of transporters that mediate the transmembrane transport of both Ca2+ and metal ions, and they are widely involved in regulating plant growth and development and stress responses. Here, we cloned an AtCAX2 ortholog, MdCAX2L-2, from apple. It is constitutively expressed in various apple tissues and significantly induced by Ca2+ and Ba2+ treatments. The MdCAX2L-2 protein is located in the vacuolar membrane in both plant and yeast cells. Overexpression of MdCAX2L-2 enhanced the tolerance of the yeast mutant K667 to high concentrations of Ca2+ and Ba2+. In addition, the role of MdCAX2L-2 in modulating Ba2+ tolerance was identified using MdCAX2L-2-overexpressing transgenic Arabidopsis plants and apple calli. Comparison of growth phenotypes and stress-related physiological indexes under BaCl2 treatment indicated that MdCAX2L-2 could enhance the Ba2+ tolerance of plants by promoting Ba2+ compartmentalization into the vacuoles and eliminating excess ROS. Our results provide insights that will aid future studies examining the function of CAX proteins in regulating stress tolerance in fruit crops, as well as their underlying mechanisms.

Methyl jasmonate improves resistance in scab-susceptible Red Delicious apple by altering ROS homeostasis and enhancing phenylpropanoid biosynthesis.

Apple (Malus domestica) is an economically important rosaceous fruit crop grown at temperate climate zones. Nevertheless, its production is severely affected by scab disease caused by the ascomycetous fungus Venturia inaequalis (VI). Methyl jasmonate (MeJA) is a stress induced plant hormone, shown to induce resistance against wide range of pathogens. The current study investigated the role of MeJA in promoting scab tolerance in susceptible apple varieties through exogenous application of optimized (100 µM) MeJA concentration, followed by VI infection. According to our analysis, applying MeJA exogenously onto leaf surfaces resulted in increased membrane stability and decreased malondialdehyde levels in Red Delicious, suggesting that MeJA is capable of protecting tissues against oxidative damage through its role in restoring membrane stability. In addition, the changes in the levels of key antioxidative enzymes and reactive oxygen species (ROS) showed that exogenous MeJA maintains ROS homeostasis as well. Higher phenylalanine ammonia-lyase activity and increased accumulation of phenylpropanoids in MeJA-treated VI-infected plants indicated the MeJA reprogrammed phenylpropanoid biosynthesis pathway for scab tolerance. Our study of scab tolerance in apples induced by MeJA provides new insights into its physiological and biochemical mechanisms.