Search

Summary: The anthocyanin content is an important indicator of the nutritional value of most fruits, including apple (Malus domestica). Anthocyanin synthesis is coordinately regulated by light and various phytohormones. In this study on apple, we revealed the antagonistic relationship between light and brassinosteroid (BR) signaling pathways, which is mediated by BRASSINAZOLE‐RESISTANT 1 (MdBZR1) and the B‐box protein MdCOL6.The exogenous application of brassinolide inhibited the high‐light‐induced anthocyanin accumulation in red‐fleshed apple seedlings, whereas increases in the light intensity decreased the endogenous BR content. The overexpression of MdBZR1 inhibited the anthocyanin synthesis in apple plants. An exposure to a high‐light intensity induced the degradation of dephosphorylated MdBZR1, resulting in functional impairment.MdBZR1 was identified as an upstream repressor of MdCOL6, which promotes anthocyanin synthesis in apple plants. Furthermore, MdBZR1 interacts with MdCOL6 to attenuate its ability to activate MdUFGT and MdANS transcription. Thus, MdBZR1 negatively regulates MdCOL6‐mediated anthocyanin accumulation.Our study findings have clarified the molecular basis of the integration of light and BR signals during the regulation of anthocyanin biosynthesis, which is an important process influencing fruit quality. [ABSTRACT FROM AUTHOR]

SUMMARY: Anthocyanins are important secondary metabolites in plants. They are important for human health because of their antioxidant activities and because their dietary intake reduces the incidence of cardiovascular and cerebrovascular diseases and tumors. The biosynthesis of anthocyanins and its regulation in fruits and vegetables is a global research hotspot. Compared with cultivated apples, the red‐fleshed apple is a relatively new and popular commodity in the market. Previous studies on red‐fleshed apples have focused on the basis for the high anthocyanin content and the transcriptional regulation of anthocyanin synthesis. In the present study, we focused on the mechanism of microRNA‐mediated post‐transcriptional regulation of anthocyanin synthesis in red‐fleshed apples. We identified a microRNA (miRNA), designated mdm‐miR858, that is specifically expressed in the flesh of apple fruit. The expression level of miR858 was significantly lower in red‐fleshed apples than in white‐fleshed apples. The overexpression of mdm‐miR858 significantly inhibited anthocyanin accumulation, whereas the silencing of mdm‐miR858 promoted anthocyanin synthesis in STTM858 transgenic apple calli. Further analyses showed that mdm‐miR858 targets the transcription factor genes MdMYB9 and MdMYBPA1 to participate anthocyanin accumulation in apple. Our results also show that MdHY5, a transcription factor in the light signaling pathway, can bind to the promoter of mdm‐miR858 to inhibit its transcription, thereby regulating anthocyanin synthesis. Based on our results, we describe a novel HY5‐miR858‐MYB loop involved in the modulation of anthocyanin biosynthesis. These findings provide new information about how plant miRNAs regulate anthocyanin anabolism and provide a basis for breeding new anthocyanin‐rich, red‐fleshed apple varieties. Significance Statement: Compared with cultivated apples, red‐fleshed apples have higher anthocyanin contents. The miRNA mdm‐miR858 is specifically expressed in the flesh of apples and targets two transcription factor genes, MdMYB9 and MdMYBPA1, to participate anthocyanin accumulation; further, a novel HY5‐miR858‐MYB loop participates in regulating anthocyanin synthesis in apple in response to light. [ABSTRACT FROM AUTHOR]

Fusarium solani has often been isolated from replanted apple roots, suggesting that it is associated with apple replant disease. The mechanism underlying the ability of the mixed cropping of apple trees with Allium fistulosum L. to alleviate apple replant disease remains unclear. The aim of this study was to determine the pathogenicity of the Fusarium solani isolate HBH 08 isolated from diseased roots and the effect of A. fistulosum L. and its root secretions on Fusarium solani isolate HBH 08 and apple seedings. The field experiment showed that A. fistulosum L. not only significantly reduced the amount of the Fusarium solani isolate HBH 08 in replanted soil but also increased the biomass of the grafted apple seedlings. The GC–MS analysis indicated that dimethyl disulphide and diallyl disulphide were active molecules in the root exudates of A. fistulosum L. They inhibited the growth of the Fusarium solani isolate HBH 08 mycelium and decreased the number of spores germinated. In addition, these compounds reduced the amount of the Fusarium solani isolate HBH 08 under replanted conditions and promoted the growth of grafted apple seedlings. Overall, mixed cropping with A. fistulosum L. might be an effective approach for cultivating apple trees and controlling apple replant disease. [ABSTRACT FROM AUTHOR]

Background: Apple (Malus domestica Borkh.) is an important economic crop. The pathological effects of Fusarium solani, a species complex of soilborne pathogens, on the root systems of apple plants was unknown. It was unclear how mycorrhizal apple seedlings resist infection by F. solani. The transcriptional profiles of mycorrhizal and non-mycorrhizal plants infected by F. solani were compared using RNA-Seq. Results: Infection with F. solani significantly reduced the dry weight of apple roots, and the roots of mycorrhizal apple plants were less damaged when the plants were infected with F. solani. They also had enhanced activity of antioxidant enzymes and a reduction in the oxidation of membrane lipids. A total of 1839 differentially expressed genes (DEGs) were obtained after mycorrhizal and non-mycorrhizal apple plants were infected with F. solani. A gene ontogeny (GO) analysis showed that most of the DEGs were involved in the binding of ADP and calcium ions. In addition, based on a MapMan analysis, a large number of DEGs were found to be involved in the response of mycorrhizal plants to stress. Among them, the overexpressed transcription factor MdWRKY40 significantly improved the resistance of the apple 'Orin' callus to F. solani and the expression of the resistance gene MdGLU by binding the promoter of MdGLU. Conclusion: This paper outlines how the inoculation of apple seedlings roots by arbuscular mycorrhizal fungi responded to infection with F. solani at the transcriptional level. In addition, MdWRKY40 played an important role in the resistance of mycorrhizal apple seedlings to infection with F. solani. [ABSTRACT FROM AUTHOR]

Background: Light quality significantly affects plant growth and development, photosynthesis, and carbon and nitrogen metabolism. Apple (Malus domestica Borkh.) is a widely cultivated and economically important fruit crop worldwide. However, there are still few studies on the effects of different light qualities on the growth and development of apple seedlings. Results: In this study, we explored the effects of blue and red light treatments on the growth and development, photosynthetic characteristics, leaf chloroplast ultrastructure, and carbon and nitrogen metabolism of apple seedlings. Blue light significantly inhibited apple plant growth and leaf extension, but it promoted the development of leaf tissue structures and chloroplasts and positively affected leaf stomatal conductance, the transpiration rate, and photosynthetic efficiency. The red light treatment promoted apple plant growth and root development, but it resulted in loosely organized leaf palisade tissues and low chlorophyll contents. The blue and red light treatments enhanced the accumulation of ammonium nitrogen in apple seedlings. Moreover, the blue light treatment significantly promoted nitrogen metabolism. Additionally, an RNA-seq analysis revealed that both blue light and red light can significantly up-regulate the expression of genes related to carbon and nitrogen metabolism. Blue light can also promote amino acid synthesis and flavonoid metabolism, whereas red light can induce plant hormone signal transduction. The expression of a gene encoding a bHLH transcription factor (MYC2-like) was significantly up-regulated in response to blue light, implying it may be important for blue light-mediated plant development. Conclusions: Considered together, blue and red light have important effects on apple growth, carbon and nitrogen metabolism. These findings may be useful for determining the ideal light conditions for apple cultivation to maximize fruit yield and quality. [ABSTRACT FROM AUTHOR]

Flavonoid content, which is an important indicator of the nutritional value of fruits and vegetables, directly determines the marketability of many fruit crops, including apple (Malus domestica). Brassinosteroids (BRs) are steroid hormones that affect flavonoid biosynthesis in plants, but the underlying regulatory mechanism remains unclear. In this study, treatments with brassinolide (the most active BR) and brassinazole (a BR biosynthesis inhibitor) decreased and increased, respectively, the flavonoid, anthocyanin, and proanthocyanidin (PA) content in red-fleshed apple seedlings and calli. We subsequently demonstrated that a BZR (BRI1-EMS-suppressor (BES)/brassinazole-resistant) family transcription factor, MdBEH2.2, participates in BR-regulated flavonoid biosynthesis. Specifically, MdBEH2.2 inhibits the accumulation of flavonoids, anthocyanins, and PAs in apple seedlings; however, brassinazole treatment weakens the inhibitory effect. Additionally, we confirmed that a BR-induced MYB TF, MdMYB60, interacts with MdBEH2.2. The resulting MdBEH2.2–MdMYB60 complex further enhances the inhibitory effect of MdBEH2.2 or MdMYB60 on the transcription of flavonoid biosynthesis-related genes. These results indicate that brassinolide decreases flavonoid content through the MdBEH2.2–MdMYB60 regulatory module. Our findings further clarify the molecular mechanism mediating the regulation of flavonoid biosynthesis by BR signals in horticultural crops. [ABSTRACT FROM AUTHOR]

Apple replant disease (ARD) is an important problem in the production of apple. The phenolic acid is one of the causes of ARD. How phenolic acid affects the ARD was not well known. In this study, we analyzed the type, concentration and annual dynamic variation of phenolic acid in soil from three replanted apple orchards using an accelerated solvent extraction system with high performance liquid chromatography (ASE-HPLC). We found that the type and concentration of phenolic acid were significantly differed among different seasons, different sampling positions and different soil layers. Major types of phenolic acid in three replanted apple orchards were phlorizin, benzoic acid and vanillic aldehyde. The concentration of phenolic acid was highest in the soil of the previous tree holes and it was increased from the spring to autumn. Moreover, phenolic acid was primarily distributed in 30–60 cm soil layer in the autumn, while it was most abundant in 0–30 cm soil layer in the spring. Our results suggest that phlorizin, benzoic acid and vanillic aldehyde may be the key phenolic acid that brought about ARD in the replanted apple orchard. [ABSTRACT FROM AUTHOR]

• Ammonium bicarbonate can enhance the growth of replanted apple trees. • Ammonium bicarbonate reduces the presence of Fusarium in replanted soil. • Soil properties influence plant growth by altering fungal biomass and soil enzyme in replanted soil. Providing nitrogen is the core of increasing production in modern agricultural systems, as well as in the production of fruit trees. The rational application of nitrogen is an important measure to increase production and sustainably utilize agricultural ecosystems. Greenhouse, pot and field experiments were conducted to study the effects of different nitrogen forms on the antifungal effect in vitro , apple growth status and the soil environment under replant condition, aims to provide a basis for scientific fertilization and alleviates apple replant disease during orchard construction. We investigated the growth of apple in replant soil treated with different forms of nitrogen, including ammonium nitrogen (NH 4 N), nitrate nitrogen (NO 3 N) and amide nitrogen (CO(NH 2) 2). The results showed that ammonium bicarbonate can inhibit the mycelial growth, spore germination and toxins synthesis of soil-borne pathogens in vitro. The addition of ammonium bicarbonate significantly promoted the replanted apple growth. The activities of soil sucrase, urease, phosphatase and catalase were higher following treatment with ammonium bicarbonate than in the control soil. The qPCR analysis showed that the bacterial, fungal biomass differed distinctly between the different nitrogen forms and the control. These results suggest that ammonium bicarbonate can inhibit the mycelial growth, spore germination and toxins synthesis of soil-borne pathogens, improve the activities of soil enzymes and change soil microbial biomass. These changes can promote growth ofreplanted apple, thereby, ammonium bicarbonate can be used to alleviate apple replant disease as a new control measure. [ABSTRACT FROM AUTHOR]

• The growth of malus robusta Rehd. was better than that of M9T337. • The metabolic activity of soil microorganisms of malus robusta Rehd. is strong. • The number of soil fungi in malus robusta Rehd. was small, and the beneficial bacteria were enriched. • Malus robusta Rehd. has a good effect on the improvement of replanted soil environment. • Malus robusta Rehd. is more suitable than M9T337 as rootstock for ARD control. Apple replant disease (ARD) seriously restricts the development of the apple industry. It is of great significance for the sustainable development of the apple industry to alleviate ARD by using rootstock resistance. Taking M9T337 and Malus robusta Rehd. as test materials, the differences in biomass, soil physical and chemical properties, soil enzyme activity, soil microbial metabolic activity and carbon source utilization characteristics, soil microbial quantity, and soil fungal community of two apple rootstocks in replanted soil. The results showed that the biomass, related soil enzyme activities, and AWCD metabolic activity of apple saplings with Malus robusta Rehd. as rootstock were better, the number of soil fungi and the copy number of four Fusarium genes were lower, and more beneficial bacteria were enriched. In conclusion, the apple saplings with Malus robusta Rehd. as rootstock have a better improvement effect on the replanted soil environment and are more suitable as rootstocks to prevent and control ARD than M9T337. [ABSTRACT FROM AUTHOR]

• Rhizopus oryzae XERF-1 was widely distributed in the apple producing areas in China. • XERF-1 fertilizer optimizes microbial community structure in replanted apple soil. • XERF-1 can be used as a biological control agent for apple replant disease. The endophytic fungus Rhizopus oryzae XERF-1 was isolated from healthy roots of apple trees growing under replanted conditions and shown to have a strong competitive antagonistic effect against ARD (Apple Replant Disease)-related pathogenic Fusarium spp. (Fusarium oxysporum, Fusarium moniliforme, Fusarium proliferatum , and Fusarium solani). The inhibition rate of mycelial growth on PDA medium was more than 75%, and the antagonistic coefficient reached level I. Pot experiment showed that treatment with an XERF-1 fertilizer significantly increased the growth of Malus hupehensis Rehd. seedlings, increased soil enzyme activities, root antioxidant enzyme activities, root architectural parameters, photosynthetic parameters, and the number of bacteria in replant soil, and reduced the number of soil fungi. Fluorescence The qPCR results showed that XERF-1 fertilizer significantly reduced the abundance of F. oxysporum in the soil, which was consistent with the high-throughput sequencing results, the relative abundance of the harmful Fusarium spp. was significantly reduced. In summary, XERF-1 has significant potential as a biological control agent against ARD. [ABSTRACT FROM AUTHOR]

Salt stress greatly hinders plant growth and development, as well as crop production. To expand the planting area and choose salt-resistant varieties of apple (Malus × domestica), it is necessary to elucidate the salt-resistance mechanisms. Here, we identified a salt-responsive WRKY transcription factor, MdWRKY55. The overexpression of MdWRKY55 in apple calli significantly improved salt tolerance. MdWRKY55 bound to the MdNHX1 promoter, thereby enhancing its transcription. MdNAC17-L significantly promoted the effect of MdWRKY55 on the expression of downstream MdNHX1 by forming a protein complex. The functional analysis of MdWRKY55 provided valuable insights into the apple salt-tolerance regulatory network and established a theoretical basis for the molecular breeding of salt-tolerant apple. • Identified a salt-responsive WRKY transcription factor, MdWRKY55. • MdWRKY55 overexpression in apple calli significantly improved salt tolerance. • MdWRKY55 bound to the MdNHX1 promoter, enhancing its transcription. • MdNAC17-L significantly promoted MdWRKY55′s effect on downstream MdNHX1 expression. [ABSTRACT FROM AUTHOR]

Apple replant disease is common in apple cultivation, leading to decay and necrosis of the root tip, growth retardation, and even death of the plant. Biological control, inducing activation of the plant's defense systems, is a promising alternative strategy for controlling the disease. In this study, we used the common rootstock 'M9T337' as the test material and harvested the plants at 60 and 120 days after transplantation. We investigated the physiological effects of inoculating the soil with indigenous arbuscular mycorrhizal fungi (AMF) to improve the resistance of the apple rootstock under replant conditions. The Glomus sp. and Paraglomus sp. acted as the major fungal species in QX and LZ. The results showed that inoculation of indigenous AMF increased the biomass of the plants and promoted root growth under replanting conditions. The antioxidant and defense-related enzyme activities in the plants were significantly raised, including the activities of the enzymes superoxide dismutase, peroxidase, catalase, ascorbate peroxidase, phenylalanine ammonia-lyase, and polyphenol oxidase. In the seedling root system, the H 2 O 2 content and O 2 ·− production were reduced, resulting in decreased lipid oxidation. Indigenous AMF treatment also induced the activity of chitinase and β-1,3-glucanase. This suggests that inoculation of indigenous AMF enhances the resistance of apple rootstock by regulating root reactive oxygen species levels and the antioxidant system under replanting conditions. This provides a theoretical basis for the prevention and treatment of apple replant disease. • The inoculation of indigenous AMF can promote root growth under replanting condition. • The indigenous AMF to replanting soil significantly increased antioxidant enzyme activity. • The H 2 O 2 content and O 2 − production rate was decreased, and lipid oxidation was reduced in apple seedling root. • The indigenous AMF therapy also induced the activity of chitinase and β-1,3-glucanase. [ABSTRACT FROM AUTHOR]