Uptake of glucose from the rhizosphere, mediated by apple MdHT1.2, regulates carbohydrate allocation

Crop cultivation without nitrogen fertiliser using nitrogen-fixing cyanobacterial extracts for low environmental impact

In this study, we attempted to develop a biological fertiliser using the nitrogen-fixing cyanobacterium, Trichormus sp. PCC7120, with the aim of constructing a sustainable farming method for growing crops without chemical fertilisers. We attempted to hydroponically culture two types of rice (Oryza sativa L. 'Sasanishiki' and 'Koshihikari'), broccoli (Brassica oleracea var. italica), and melon (Cucumis melo L.) using intracellular extracts from Trichormus sp. PCC7120, which was prepared using heat treatment or acid hydrolysis. Early crop growth, including length and weight, was compared among three groups: (i) pure water, (ii) chemical fertiliser, and (iii) Trichormus extract groups. Sasanishiki grew most efficiently in the 80% heat-treated and 2.5% acid-hydrolysed extracts than in pure water, whereas Koshihikari grew most efficiently in the 40% heat-treated extract than in pure water. Sasanishiki and Koshihikari consumed ammonium, potassium, and various proteinogenic amino acids in the Trichormus extract. Broccoli exhibited more length and weight when cultivated with 10-20% acid-hydrolysed extracts than in pure water and consumed glucose, along with phosphorus and glycine, in the extract. Melon exhibited more length and weight when cultivated with 10% acid-hydrolysed extracts than in pure water and actively consumed glucose, serine, glycine, and alanine in the extract. Crop growth with Trichormus extracts was comparable with that of the chemical fertiliser group. This report shows that ammonium, phosphorus, potassium, glucose, and amino acids in nitrogen-fixing cyanobacterial extracts contribute to crop growth, and these extracts may thus be valuable as biological fertilisers in crop cultivation.

Integrated metabolome analysis and transcript profiles revealed a potential role of SWEETs in sugar accumulation during Carrot taproot development

BACKGROUND

Carrot is a root vegetable abundant in numerous nutritional values. Sugar is one of the most important carbohydrates in horticultural products that play important roles in plant growth and development and response to biotic and abiotic stresses. However, the dynamics of the metabolites including sugar during carrot root development still remain unclear. Here, the differential metabolites in carrot roots at different developmental stages were measured using an UPLC-ESI-MS/MS system. The accumulation profiles of metabolites, especially sugars, as well as the transcript patterns of Sugars Will Eventually be Exported Transporter (SWEET) genes were intensively examined.

RESULTS

The results identified 727 metabolites over all the samples detected, of which, 539 metabolites were found to be differential accumulated. A total of 34 differentially accumulated sugar metabolites were identified over the period of root development. Furthermore, 17 DcSWEET genes were detected to be specifically expressed in the roots, indicating a potential for root enlargement and sugar accumulation in carrot root.

CONCLUSIONS

The results from the current study would help carrot breeding focused on yield and quality improvement.

Expression of the polyphenol oxidase gene MdPPO7 is modulated by MdWRKY3 to regulate browning in sliced apple fruit

Browning is a pervasive problem in horticultural products, substantially diminishing the appearance, flavor, and nutritional value of fruit, including important fruits like apple (Malus × domestica Borkh.). In this study, we compared the physiological characteristics of the browning-resistant line 'Rb-18' with the susceptible variety 'Fuji' and found that the polyphenol oxidase (PPO) enzyme activity and phenolic content of 'Rb-18' were significantly lower than those in 'Fuji'. In addition, the PPO enzyme in 'Fuji' showed a stronger affinity for its substrate, catechol, compared to 'Rb-18'. Through transcriptome and RT-qPCR analyses, MdPPO7 expression was identified as contributing to flesh browning after cutting. Subsequent fruit injection and stable genetic transformation of the MdPPO7 gene into apple fruit and calli determined that syringic acid, procyanidin, phloridzin, chlorogenic acid, gallic acid, catechin, and caffeic act as its catalytic substrates in the process involved in browning. Furthermore, luciferase reporter, yeast 1-hybrid, β-glucuronidase reporter assays and ChIP-qPCR analysis demonstrated that a WRKY transcription factor (MdWRKY3) binds to the promoter region of polyphenol oxidase gene (MdPPO7) and positively regulates its expression to promote apple flesh browning. This study provides insights into the molecular regulatory mechanisms of fruit browning in fresh-cut apples and provides a theoretical basis for the generation of high-quality apple germplasm resources.

Exogenous glucose irrigation alleviates cold stress by regulating soluble sugars, ABA and photosynthesis in melon seedlings

Melon (Cucumis melo L.) is an important economic crop and widely planted around the world. Cold stress severely limits its development and yield. Carbohydrates play multiple roles in plant cold tolerance. However, little is known in melon. Based on the metabolome analysis, a total of 635 metabolites were identified upon cold stress in melon seedlings. KEGG analysis shows that differential metabolites were mainly enriched in the glycolysis/gluconeogenesis pathway and pentose phosphate pathway, with glucose being one of the most prominent metabolites. To further investigate the role of glucose in cold tolerance of melon seedlings. We found that root irrigation was more effective than foliar spraying for exogenous glucose application, with optimal concentrations of 0.5% and 1% for cold-tolerant and cold-sensitive genotypes, respectively. Glucose irrigation mainly promoted soluble sugar accumulation to reduce cold damage in melon seedlings. For cold-sensitive genotype, only the sucrose content could be increased, while for cold-tolerant genotype, sucrose, fructose and glucose content could be simultaneously increased. Meanwhile, glucose irrigation recruited ABA not antioxidant enzyme system to cope with cold stress. Hence, glucose watering could improve the maximum photochemical efficiency of seedling photosystem II (Fv/Fm), alleviate physiological drought, reduce the accumulation of malondialdehyde, and accelerated the photosynthetic efficiency of melon seedlings. Based on coefficient of variation and principal component analysis, it was confirmed again that glucose irrigation did alter the strategies for withstanding cold stress and enhance the cold tolerance of melon seedlings. Thus, the results would provide a theoretical basis and feasible measures to protect melon seedings from cold damage.

MdSINA2-MdNAC104 Module Regulates Apple Alkaline Resistance by Affecting γ-Aminobutyric Acid Synthesis and Transport

Soil alkalization is an adverse factor limiting plant growth and yield. As a signaling molecule and secondary metabolite, γ-aminobutyric acid (GABA) responds rapidly to alkaline stress and enhances the alkaline resistance of plants. However, the molecular mechanisms by which the GABA pathway adapts to alkaline stress remain unclear. In this study, a transcription factor, MdNAC104 is identified, from the transcriptome of the alkaline-stressed roots of apple, which effectively reduces GABA levels and negatively regulates alkaline resistance. Nevertheless, applying exogenous GABA compensates the negative regulatory mechanism of overexpressed MdNAC104 on alkaline resistance. Further research confirms that MdNAC104 repressed the GABA biosynthetic gene MdGAD1/3 and the GABA transporter gene MdALMT13 by binding to their promoters. Here, MdGAD1/3 actively regulates alkaline resistance by increasing GABA synthesis, while MdALMT13 promotes GABA accumulation and efflux in roots, resulting in an improved resistance to alkaline stress. This subsequent assays reveal that MdSINA2 interacts with MdNAC104 and positively regulates root GABA content and alkaline resistance by ubiquitinating and degrading MdNAC104 via the 26S proteasome pathway. Thus, the study reveals the regulation of alkaline resistance and GABA homeostasis via the MdSINA2-MdNAC104-MdGAD1/3/MdALMT13 module in apple. These findings provide novel insight into the molecular mechanisms of alkaline resistance in plants.

The transcription factor MdBPC2 alters apple growth and promotes dwarfing by regulating auxin biosynthesis

Auxin plays important roles throughout plant growth and development. However, the mechanisms of auxin regulation of plant structure are poorly understood. In this study, we identified a transcription factor (TF) of the BARLEY B RECOMBINANT/BASIC PENTACYSTEINE (BBR/BPC) family in apple (Malus × domestica), MdBPC2. It was highly expressed in dwarfing rootstocks, and it negatively regulated auxin biosynthesis. Overexpression of MdBPC2 in apple decreased plant height, altered leaf morphology, and inhibited root system development. These phenotypes were due to reduced auxin levels and were restored reversed after exogenous indole acetic acid (IAA) treatment. Silencing of MdBPC2 alone had no obvious phenotypic effect, while silencing both Class I and Class II BPCs in apple significantly increased auxin content in plants. Biochemical analysis demonstrated that MdBPC2 directly bound to the GAGA-rich element in the promoters of the auxin synthesis genes MdYUC2a and MdYUC6b, inhibiting their transcription and reducing auxin accumulation in MdBPC2 overexpression lines. Further studies established that MdBPC2 interacted with the polycomb group (PcG) protein LIKE HETEROCHROMATIN PROTEIN 1 (LHP1) to inhibit MdYUC2a and MdYUC6b expression via methylation of histone 3 lysine 27 (H3K27me3). Silencing MdLHP1 reversed the negative effect of MdBPC2 on auxin accumulation. Our results reveal a dwarfing mechanism in perennial woody plants involving control of auxin biosynthesis by a BPC transcription factor, suggesting its use for genetic improvement of apple rootstock.

2-NBDG Uptake in Gossypium hirsutum in vitro ovules: exploring tissue-specific accumulation and its impact on hexokinase-mediated glycolysis regulation

Fluorescent glucose derivatives are valuable tools as glucose analogs in plant research to explore metabolic pathways, study enzyme activity, and investigate cellular processes related to glucose metabolism and sugar transport. They allow visualization and tracking of glucose uptake, its utilization, and distribution within plant cells and tissues. This study investigates the phenotypic and metabolic impact of the exogenously fed glucose derivative, 2-(N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino)-2-deoxyglucose) (2-NBDG) on the fibers of Gossypium hirsutum (Upland cotton) ovule in vitro cultures. The presence of 2-NBDG in the culture medium did not lead to macroscopic morphological alterations in ovule and fiber development or to the acquisition of fluorescence or yellow coloration. Confocal laser scanning microscope imaging and chromatographic analysis of cotton ovules' outer rim cross-sections showed that the 2-NBDG is transported from the extracellular space and accumulated inside some outer integument cells, epidermal cells, and fertilized epidermal cells (fibers), but is not incorporated into the cell walls. Untargeted metabolic profiling of the fibers revealed significant changes in the relative levels of metabolites involved in glycolysis and upregulation of alternative energy-related pathways. To provide biochemical and structural evidence for the observed downregulation of glycolysis pathways in the fibers containing 2-NBDG, kinetics analysis and docking simulations were performed on hexokinase from G. hirsutum (GhHxk). Notably, the catalytic activity of heterologously expressed recombinant active GhHxk exhibited a five-fold decrease in reaction rates compared to D-glucose. Furthermore, GhHxk exhibited a linear kinetic behavior in the presence of 2-NBDG instead of the Michaelis-Menten kinetics found for D-glucose. Docking simulations suggested that 2-NBDG interacts with a distinct binding site of GhHxk9, possibly inducing a conformational change. These results highlight the importance of considering fluorescent glucose derivatives as ready-to-use analogs for tracking glucose-related biological processes. However, a direct comparison between their mode of action and its extrapolation into biochemical considerations should go beyond microscopic inspection and include complementary analytical techniques.