Phenolic acids (PAs) are important secondary metabolites that mediate plant-microbe communication and function as plant defenders, plant growth promoters, rhizosphere microbial recruiters, and interferers of microbial quorum sensing. Against the backdrop of cutting-edge biotechnologies in genomics and metabolomics, this review synthesizes frontier research on the functions and mechanisms of PAs in the aforementioned aspects, following a brief summary of their biosynthesis and chemical structures in plants. Finally, the review also suggests further research priorities, including manipulating PAs to reshape the rhizosphere microbiome, developing functional root exudate databases for precision breeding, and investigating the degradation of PAs by prebiotics to enhance agricultural sustainability. We advocate for multidisciplinary studies that integrate metabolomics, genomics, and ecology, as they offer diverse perspectives on plant-microbe interactions and provide valuable ecological insights and potential applications for sustainable agriculture.

Alfalfa (Medicago sativa L.) is one of the most widely cultivated forage crops globally. Selenium (Se) is considered beneficial for plants, showing a concentration-dependent dual effect that can promote and inhibit various plant species, including alfalfa. Long non-coding RNAs (lncRNAs), a class of non-protein-coding transcripts, are involved in multiple biological processes in plants. To explore the potential role of lncRNAs in Se accumulation and tolerance in alfalfa, physiological responses were measured, and lncRNA expression was examined in alfalfa leaves exposed to Se concentrations of 0 mg L, 100 mg L, and 500 mg L. Under selenium treatment, lipoxygenase (LOX) activity and antioxidant levels increased significantly. A total of 64,684 novel lncRNAs were identified, with 1414 and 1810 differentially expressed lncRNAs (DELs) found in the 100 mg L and 500 mg L Se-treated groups, respectively. Functional enrichment analysis suggested that LOX-targeted lncRNAs could play a pivotal role in Se accumulation and tolerance. Silencing of MslncLOX13S resulted in a yellowing of the leaf edges and lowered levels of LOX, jasmonic acid (JA), antioxidant capacity, and Se content. In comparison, transient overexpression of MslncLOX13S showed the opposite effects. These findings may contribute to the development of alfalfa cultivars enriched in Se, suitable for use as feed or raw material for organic Se extraction. Moreover, this study improves the understanding of lncRNA-mediated gene expression in alfalfa, highlighting MslncLOX13S as a Se-responsive lncRNA that enhances tolerance against Se, potentially offering a strategy for improving Se biofortification in forage crops.

Mature non-stressed plants often contain a lot more chlorophyll than they need to efficiently capture light energy in the PAR range. In this situation, some pigment molecules apparently become physiologically redundant because they remain shaded and cannot participate efficiently in light harvesting. As a result of the build-up of chlorophyll, strong absorption of these pigments extends well beyond 700 nm, the conventional border of PAR, into far red (FR) region of the spectrum (to 750 nm and beyond) contributing significantly to the budget of the absorbed light energy. It is also well known that FR light, when supplemented to conventional PAR spectrum, harmonizes energy flow in the photosynthetic apparatus, reduces risk of photodamage boosting plant productivity. We argue that a possible functional role of the "redundant chlorophyll" accumulated in plants is ensuring the capture of FR photons. The latter is among important acclimations to fluctuating light fluxes as well as to permanently low-light environments ensuring efficient operation of complex plant canopies. We discuss the opportunity to harness the "FR boost" of productivity by leveraging inherent optical properties of green plants without sophisticated approaches such as engineering of long-wave chlorophylls into the plant photosynthetic apparatus.

Protoplasts are widely used in the fields of genetic transformation, physiology, and biochemistry, as they can easily absorb exogenous substances. The development and an efficient protoplast isolation and transient transformation system are essential for molecular biology and related research. Toona ciliata, valued for its high-quality and vividly colored wood, represents an economically significant species. In order to promote efficient breeding of the precious fast-growing tree, the establishment of a protoplast isolation and transient transformation system for T. ciliata is particularly important.

Strawberry (Fragaria × ananassa Duch.) is sensitive to salt stress. The application of exogenous 5-aminolevulinic acid (ALA) can induce chloride channel (CLC) gene expression, which promotes Cl retention in roots with less translocation to shoots, thereby improving the salt tolerance of plants. However, the underlying transcriptional regulatory mechanism remains unknown. In this study, 23 FaCLC genes were identified in the strawberry genome, which were classified into two subclasses and six subgroups. NaCl stress stimulated the expression of FaCLC-b1/c4/e3 in the leaves and roots of strawberry and ALA further promoted the gene expression under salt stress. NaCl and ALA activated the transcriptional activity of three gene promoters, as detected by using β-glucuronidase (GUS) reporter gene. Subcellular localization analysis revealed that FaCLC-b1 and FaCLC-c4 are tonoplast localized proteins. Overexpression of FaCLC-b1 and FaCLC-c4 in tobaccos improved the salt tolerance of transgenic plants with more Cl retention in the roots and less accumulation in the leaves. It was found that the NO content was increased by ALA treatment. Moreover, we identified a nucleus-localized transcription factor FaMYB44. Verification by yeast one-hybrid assay (Y1H), dual-luciferase reporter (LUC), and electrophoretic mobility shift assay (EMSA) demonstrated that FaMYB44 can recognize the MBS elements of the promoter of FaCLC-c4 and negatively regulate the target gene expression. NaCl stress induced FaMYB44 expression in strawberry roots, while ALA suppressed its expression. Overexpression of FaMYB44 in tobacco resulted in increased Cl accumulation in the leaves and impaired the plants. FaMYB44 can bind to the promoter of FaCLC-c4 and depress its expression, while ALA inhibited FaMYB44 expression, thereby alleviating the suppression of FaMYB44 on FaCLC-c4 expression, and intercepting Cl in roots with preferential transport of NO up to the leaves and increasing salt tolerance. These findings provide a new perspective on the transcription regulation of FaCLC genes and facilitate better application of exogenous ALA in salt tolerance practices for fruit production.

SHORT INTERNODES (SHI)-related sequence (SRS) proteins are plant-specific transcription factors that modulate hormone biosynthesis and signalling. Their contribution to legume-rhizobium symbiosis, however, remains largely unexplored. Phylogenetic and collinearity analyses of legume SRS genes classified 12 subclasses and revealed soybean's evolutionary relationships, including large-scale gene duplication. GmSRS14 was specifically highly expressed in root nodules and localised in the nucleus only. Exogenous IAA modulates its expression at low concentrations (1 μM), while high concentrations (100 μM) decrease nodule expression. All ABA concentrations tested (10, 20 and 50 μM) inhibited nodule growth, nitrogenase activity and GmSRS14 expression. Functional validation via hairy root transformation demonstrated GmSRS14 overexpression (GmSRS14-OE) increased nodule number, weight, and nitrogenase activity, while GmSRS14 silencing (GmSRS14-RNAi) suppressed nodulation. This study provides a new idea for breeding soybean varieties with high efficiency of nitrogen fixation.

In tank-forming epiphytic bromeliads, two distinct growth stages can be easily identified, each characterized by specific adaptive traits for capturing nutrients such as inorganic or organic nitrogen sources: (a) the juvenile stage (atmospheric form), during which the bromeliad absorbs nutrients dissolved in rainwater through its leaves and roots; and (b) the adult stage (tank form), in which overlapping leaves form a reservoir that enables the accumulation of water and nutrients among the leaf bases. This study investigated differences in nitrogen absorption, translocation, and assimilation between these two growth stages of Vriesea gigantea. Atmospheric and tank-form bromeliads were supplied with solutions containing NO, NH, or [U-N]urea. Leaves and roots were harvested at six different time points and used for enzymatic activity assays (urease, nitrate reductase, glutamine synthetase, glutamate dehydrogenase) and endogenous content quantifications (ammonium, nitrate, and N abundance). Ammonium and urea were the main nitrogen sources utilized by both growth forms. However, they were not absorbed and assimilated with equal efficiency: atmospheric bromeliads used ammonium more efficiently, whereas tank bromeliads utilized urea better. Although nitrate was the least absorbed source in both plants, atmospheric bromeliads showed faster uptake and assimilation. These findings suggest that inorganic nitrogen sources may be more readily available to epiphytic bromeliads during their juvenile phase, which could explain why they are physiologically better adapted to absorb and metabolize them. In the adult stage, organic nitrogen sources may become more accessible to V. gigantea, as the tank structure facilitates the accumulation of decomposing organic matter.

An efficient genetic transformation system is imperative for advancing gene functional studies and molecular breeding in horticultural tree species. Traditional Agrobacterium tumefaciens-mediated methods have encountered significant technical challenges when applied to tree species, particularly Liriodendron hybrids. The high costs, and extended transformation cycles associated with this method have substantially limited its utility in gene functional analysis and breeding applications. In response to these challenges, this study presents the development of a streamlined, rapid, and efficient Agrobacterium rhizogenes-mediated transformation system tailored specifically for Liriodendron hybrids, an important ornamental and timber tree species. Among the three Agrobacterium rhizogenes strains (K599, MSU440, and C58C1) evaluated in this study, K599 demonstrated the highest transformation efficiency, reaching 46.09 % for inducing hairy roots from apical bud incisions. Further optimization of the system revealed that 2 days and two-month-old seedlings were the most suitable co-culture duration and explants, yielding a peak transformation efficiency of 60.38 %, 53.12 %, respectively. The applicability of this transformation system was validated across various Liriodendron hybrids genotypes and Liriodendron tulipifera, with transformation efficiencies ranging from 15.47 % to 60.63 %. Additionally, the system was effectively employed for subcellular localization analysis, which confirmed that the aquaporin (AQP) protein. LhAQP1 is localized in the plasma membrane and exhibits enrichment in the vascular tissues of the hairy roots. Notably, this study marks the first application of the Agrobacterium rhizogenes-mediated system for CRISPR/Cas9-mediated gene editing in Liriodendron hybrids, successfully achieving targeted mutagenesis of the LhAQP1 gene and establishing the feasibility of gene editing within this species. In addition, the hairy root-based transformation system was employed to investigate the functional role of LhAQP1 in the improved Liriodendron variety 'Nanlin-Jinsen E1' by comparing wild-type, LhAQP1-overexpressing and gene-edited lines generated via the CRISPR/Cas9. LhAQP1-overexpression significantly promoted plant growth and drought tolerance, whereas pYLCRISPR-LhAQP1 increases dehydration sensitivity, underscoring the essential role of LhAQP1 in water stress adaptation. Optimized transformation platform represents a crucial advancement for functional genomics and molecular breeding efforts in woody plants.

Botrytis cinerea (B. cinerea) is a typical necrotrophic fungal pathogen causing severe yield losses in crops and fruits, But the molecular defense mechanism of plants against this fungus is not fully understood. Here in our study, C3H23 was found to positively regulate plant defense against B. cinerea in Arabidopsis thaliana. c3h23 mutant showed decreased expression of JA/ET-responsive genes and compromised defense against B. cinerea. In contrast, overexpression of C3H23 increased the expression of JA/ET-responsive genes and enhanced plant resistance. In addition, C3H23 was transcriptionally activated by WRKY33, which directly bound to a W-box in the promoter of C3H23. Furthermore, expression of C3H23 was down-regulated in wrky33 mutants compared to that in wild-type plants responding to B. cinerea infection. Genetic analysis revealed that WRKY33 controlled the defense to B. cinerea in a partial C3H23-dependent manner. In summary, C3H23 regulates the defense to B. cinerea positively by inducing JA/ET signaling and being targeted transcriptionally by WRKY33 in Arabidopsis thaliana.

Soil salinization is one of the critical challenges facing global agriculture, seriously affecting crop growth and yields. As the primary organs for absorbing water and nutrients, plant roots play a pivotal role in responding to salt stress. In recent years, researchers have uncovered diverse functional mechanisms underlying root-mediated salt tolerance through multi-dimensional studies, such as gene regulation, physiological and biochemical mechanisms, and ecological adaptation. This article reviews the integrated functions of plant roots in salt tolerance from multiple perspectives, including root structure and function, physiological and biochemical responses of roots, root-shoot coordination, root perception and signal transduction of salt stress, rhizosphere microbial synergy, nutrient elements, and the application of phenotypic techniques. Such knowledge is expected to provide a theoretical foundation for breeding salt-tolerant crop varieties.

Increased temperature is one of the most important environmental factors affecting plant life. Here, the effect of heat (40 °C, 3 h) on thylakoid O production and mitochondrial O consumption, HO and superoxide generation, an accumulation of malondialdehyde (MDA) in organelles, ascorbate peroxidase activities, redox state of ascorbate and glutathione pools were investigated in the developing primary leaf of Hordeum vulgare L. (4-, 7- and 11-day-old seedlings: 'young', 'mature' and 'aging' leaf, respectively). It was found that heat inhibited chloroplast O-evolving activity in the leaf of all ages. Heat increased respiration in young leaf and decreased it in 7- and 11-day-old seedlings. In chloroplasts, heat mainly increased the ROS production in aging leaf although it did not cause accumulation of MDA (marker of lipid peroxidation). These effects were accompanied by enhanced ROS production and accumulation of MDA in mitochondria in all age groups. Heat-induced generation of ROS in chloroplasts of older leaf caused activation of ascorbate peroxidase, resulting in a decrease in the amount of ascorbate. At the same time, the reduced glutathione content was increased in heated leaf of all ages with partially high levels in older leaf. Heat also activated NADPH oxidase in leaves of 4-day-old seedlings but not in older leaf that can be reminiscent of elevated NADPH oxidase activity in growth tissues. The discovered generation of ROS and other effects were analyzed in the context of the heat-induced modification of photosynthetic electron flows in the developing primary leaf of barley, which we previously revealed. Schemes of possible heat-induced reactions for different stages of leaf development were proposed.

Calcium (Ca) plays versatile roles in plant growth and development, as well as in responses to environmental stimuli. Abiotic stressors, including abnormal temperature, drought, salt, heavy metals, and flooding, induce instantaneous and rapid free cytosolic Ca ([Ca]) elevation, known as Ca signatures. Ca signatures are stress-specific and regulated by Ca flux. Ca flux contains Ca influx, which initiates Ca signatures, and Ca efflux, which terminates them. Ca flux is achieved through the co-operation of Ca channels and pumps. Here, we highlight recent advances in Ca flux and Ca channel functions in plant responses to abiotic stress. Ca influx channels in plants include the hyperosmolarity-gated calcium-permeable channel family of proteins (OSCAs), glutamate receptor-like channels (GLRs), cyclic-nucleotide-gated calcium channels (CNGCs), annexins (ANNs), two-pore channels (TPCs), Piezo channels (PZOs), Mid1-complement activity protein channels (MCAs), and mechanosensitive channels of small conductance (MscS)-like proteins (MSLs). Ca efflux channels mainly contain Ca-ATPases and Ca exchangers. Most Ca channels have been found to participate in plant responses to single abiotic stress, whereas some are reported to be involved in responses to multiple abiotic stresses. This improved knowledge advances our understanding of Ca signaling in plant responses to abiotic stress and offers new strategies for cultivating stress-resilient crops.

Intragenesis is classified as New Plant Breeding Techniques and agroinfiltration provides a simple, rapid and reproducible technique for transient gene expression. Sexual compatibility is a perquisite for the use of interspecies genetic components. In the present study, genetic crosses between Nicotiana benthamiana and N. tabacum have been achieved and viable progeny obtained. Resulting F progeny were phenotyped and classification into three groups was observed. These phenotypes included N. benthamiana Lab-like phenotypes termed "BEN", representing 64 % of the progeny, while 8 % had observable N. tabacum phenotypes termed "TAB". Finally, 28 % represented a hybrid phenotype "HYB". Male sterility was present in group TAB and HYB. In order to assess the amenability of the progeny to agroinfiltration and to evaluate the potential of the new chassis with increased biomass and growth properties, the transient production of ketocarotenoids was performed. The progeny with BEN phenotypes showed increased ketocarotenoid production (∼1330 μg/g DW) compared to the control (∼550 μg/g DW). However, the increased leaf size found in the TAB and HYB progeny yielded greater ketocarotenoid levels per leaf (∼800 and ∼700 μg/g DW), when compared to the traditional N. benthamiana Lab accession. Further progeny of BEN and clonally propagated HYB were tested, but the beneficial traits for transient expression could only be attributed to the F progeny cultivated from seed.

This study characterized the function of CpWRKY51, a WRKY transcription factor from Cucurbita pepo, and explored its role in responding to salt and drought stresses. The function of the CpWRKY51 gene was verified using a virus-mediated transient overexpression system. After salt and drought stress treatments, C. pepo plants with transient overexpression of CpWRKY51 showed significantly milder wilting symptoms than the control group; similarly, Arabidopsis thaliana with CpWRKY51 overexpression also exhibited stronger tolerance to salt and drought stresses. Physiological detection revealed that under stress conditions, the accumulation of reactive oxygen species (ROS) such as malondialdehyde (MDA), superoxide anion (O), and hydrogen peroxide (HO) in the leaves of CpWRKY51-overexpressing lines was reduced, while the activities of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) were significantly higher than those in the control group. At the molecular mechanism level, DNA Affinity Purification Sequencing (DAP-seq) identified the canonical W-box motif ("TTGAC") as the core binding sequence of CpWRKY51. Electrophoretic mobility shift assay (EMSA) and yeast one-hybrid (Y1H) assay confirmed that CpWRKY51 could specifically bind to the promoter of Pyrabactin Resistance 1-Like 2 (PYL2). Yeast two-hybrid (Y2H) assay and bimolecular fluorescence complementation (BiFC) assay showed that PYL2 could interact with Protein Phosphatase 2C (PP2C1 and PP2C4) in the presence of 10 μM ABA, and CpSnRK2.6 from C. pepo could specifically interact with PP2C1 and PP2C4. These results indicate that CpWRKY51 positively regulates the tolerance of Cucurbita pepo to salt and drought stresses by coordinately modulating the antioxidant defense system and the PYL-PP2C-SnRK2 pathway. This study provides a theoretical reference for elucidating the molecular mechanisms underlying WRKY transcription factor-mediated stress adaptation in horticultural crops, and clarifies that CpWRKY51 can serve as a potential target for the genetic improvement of crop stress resistance.

The transition toward sustainable agriculture requires fertilisation strategies that improve nutrient use efficiency, enhance resilience to abiotic and biotic stress, and minimise environmental impacts. Bio-based fertilisers, biostimulants, and novel delivery systems have emerged as promising alternatives or complements to conventional agrochemicals, yet their physiological bases remain only partially understood. This review examines current knowledge on the mechanistic pathways through which these products act and identifies research gaps to enable predictive use in diverse cropping systems. Evidence indicates that bio-based inputs influence plant performance by modulating nutrient uptake and assimilation, hormonal and redox signalling, stress perception and defence priming, and biomass allocation. Protein hydrolysates, humic substances, and seaweed extracts alter root morphology, ion transport, and stress signalling, while microbial inoculants such as rhizobia, phosphate-solubilising bacteria, and arbuscular mycorrhizal fungi provide nutrient mobilisation and immune priming. Novel delivery systems, including clays and encapsulation systems, extend these effects by improving the stability and targeted release of bioactive compounds. Despite these advances, the lack of standardised protocols, incomplete dose-response characterisation, and strong context dependence of plant responses remain major obstacles to reproducibility and scalability. Progress in this field requires a mechanistically anchored approach that links molecular events (such as transporter activation, hormone dynamics, and antioxidant activity) to agronomic outcomes under variable environments. Embedding mechanistic descriptors into both experimental design and regulatory frameworks could accelerate the translation of bio-based inputs into reliable tools for sustainable crop production, supported by environmental impact assessments.

Root apical meristem (RAM) maintains sustained root development, which is intricately coordinated by a series of biological processes integrating internal and external cues. Here, we present evidence that SMALL ORGAN 2 (SMO2) is required for the maintenance of RAM. Deficiency of SMO2 resulted in disorganization of the stem cell niche (SCN) and the presence of dead cells in RAM, independent of DNA damage. Moreover, following chemically induced wounding, excision of root tips, or removal of whole roots, the regeneration capacity of smo2 mutants was dramatically lower than that of wild-type plants. Mechanistically, SMO2 is necessary for 18S rRNA methylation at position G1581, which may be associated with abnormal ribosome profiles in smo2 mutants. Further analysis showed that deficiency of SMO2 markedly reduced the translation efficiency of genes involved in polar auxin transport, thereby reducing auxin accumulation in the RAM. Surprisingly, an additional deletion of ANAC082, which encodes a known transcriptional mediator of ribosomal stress-induced developmental adaptations, effectively restored the disordered SCN and cell death phenotypes in smo2 mutants. Collectively, our findings demonstrate that SMO2-mediated translational regulation plays an important role in auxin accumulation in root tips. This process appears to be essential for sustaining RAM activity, as indicated by the structural disorganization of root tips in smo2 mutants. Notably, this phenotypic manifestation is mechanistically dependent on ANAC082.

We investigated the effect of arbuscular mycorrhizal (AM) symbiosis on the triacylglycerol fatty acids (TAGFA) profile in the rhizosphere of olive trees colonized by Rhizophagus (R.) irregularis. The TAGFA 16:1ω5 was used as a marker of AM fungal storage structures, whereas TAGFA 18:2ω6 was used as a marker of saprotrophic fungal storage structures. Our results showed that the rhizospheres of AM and non-mycorrhizal (NM) plants differed significantly in their TAGFA composition, a finding reported here for the first time. In particular, root colonization by R. irregularis increased TAGFA 16:1ω5 by 76 % and decreased TAGFA 18:2ω6 by 45 %, suggesting that less carbon was allocated to saprotrophic fungal storage structures. This redistribution of carbon in AM plant rhizospheres strongly influenced the content of cyclopropyl fatty acids in microbial cytomembranes, which are widely used as classical indicators of nutritional stress in soil microorganisms. The cyclopropyl-to-precursor ratio decreased significantly in AM rhizospheres, indicating that AM symbiosis effectively alleviates microbial stress in olive rhizospheres. These marked changes in the AM rhizosphere were associated with metabolic rearrangements in olive leaves. AM symbiosis generally had a positive impact on amino acid levels, particularly those of the glutamate family (glutamic acid, arginine, ornithine, and glutamine). Metabolic reprogramming also enhanced other pathways of secondary metabolism, notably flavonoids (luteolin 7-O-glucoside and luteolin 7-O-rutinoside) and the secoiridoid oleuropein. Taken together, our results highlight the pivotal role of AM fungi in regulating the allocation of photosynthates from aboveground tissues to belowground structures, including roots and their associated mycorrhizal partners, thereby driving rhizospheric changes and priming the accumulation of defensive compounds in olive leaves. This may (1) decrease leaf water potential, making it more negative and thereby facilitating water movement from the stem to the leaves, and (2) enhance tolerance to environmental stresses.

Turfgrass species commonly used for lawns, sports fields, and urban green spaces frequently encounter salt exposure. Under conditions of salt stress, the quality of the turfgrass diminishes, leading to a loss of economic value and a reduction in its ability to serve recreational and functional purposes. Salt stress responses are critical for the survival and functionality of turfgrass in saline environments. Paspalum vaginatum (seashore paspalum), a stress-tolerant turfgrass widely used in lawns and golf courses, is an ideal model for studying plant stress adaptation. The calcium-dependent protein kinases (CDPKs) family, key regulators of plant growth, development, and stress signaling, remains uncharacterized in this species. Using evolutionarily conserved CDPK protein sequences from Arabidopsis thaliana, Oryza sativa, and Zea mays as references, we performed a genome-wide identification of CDPKs in P. vaginatum and ultimately identified 30 candidate PvCDPK genes. We analyzed conserved domains, gene structures, chromosomal distribution, and phylogenetic relationships of PvCDPKs. Promoter cis-element analysis identified phytohormone-responsive, stress-responsive, and growth/development-related motifs. Quantitative reverse transcription PCR (qRT-PCR) of PvCDPKs demonstrated tissue-specific expression profiles and differential regulation under salt stress, drought stress, cold stress, and ABA treatment conditions. Overexpression of PvCDPK5 in A. thaliana showed that the transgenic plants exhibited significantly enhanced salt tolerance, accompanied by reduced reactive oxygen species (ROS) accumulation, decreased malondialdehyde (MDA) content, increased activities of antioxidant enzymes, and improved Na/K balance. Collectively, these results suggest that PvCDPK5 regulates plant salt tolerance by mediating the alleviation of oxidative stress and maintaining ion homeostasis. Furthermore, insights into turfgrass salt adaptation can inform breeding strategies for other salt-sensitive crops, thereby enhancing agricultural productivity in salinized soils.

Sugars are not only central metabolites in plants but also act as signalling molecules that coordinate growth, development, and physiology. In the green lineage (viridiplantae), the intermediate of trehalose biosynthesis, trehalose 6-phosphate (Tre6P), has emerged as a central regulator of carbon status. In angiosperms, Tre6P signalling is integrated with energy-sensing mediated by kinases such as SnRK1 and TOR to balance growth with metabolism and environmental factors. Here we review the current knowledge on the functions of sugar signalling components in the green lineage. We put a special emphasis on Tre6P signalling as genomic, transcriptomic, and metabolomic studies across algae, bryophytes, and vascular plants indicate that Tre6P's role as a sugar signal predates the colonization of land and may have been instrumental during terrestrialization and the evolution of vascular systems. Functional studies in mosses, and angiosperms reveal conserved roles of Tre6P in vegetative growth, and the initiation of sexual reproduction, underscoring its potential as a conserved signalling metabolite. Taken together, these insights support the view that Tre6P has acted as a conserved and adaptable hub linking carbon availability to plant development and reproduction throughout plant evolution.

Biennial bearing is one of the major challenges in the commercial production of apples (Malus × domestica Borkh.). Unless a considerable portion of flowers in apple orchards is removed every year, naturally occurring high crop load (ON-year) strongly suppresses flowering in the following year, leading to low yields (OFF-year). This ON-OFF bearing cycle significantly diminishes the profitability of apple orchards. This phenomenon generally occurs in all apple varieties, but is much more pronounced in some genotypes (biennial-bearing) than in others (regular-bearing). Although apple fruits of the current season and flower buds for the next season develop simultaneously, it remains unclear whether biennial bearing is triggered by signaling compounds from the fruits or results from carbohydrate competition between growing fruits and buds. To test the carbohydrate competition hypothesis, we analyzed nine carbohydrates in bourse buds of the biennial-bearing cultivar 'Fuji' and the regular-bearing cultivar 'Gala'. Bud samples were collected from high-cropping (ON) and non-cropping (OFF) trees during the period of flower bud formation. Our results showed no evidence of carbohydrate deficiency in buds from ON-trees compared to those from OFF-trees. Contrary to the hypothesis, the concentrations of glucose and fructose in 'Gala' were higher in buds from ON-trees. Furthermore, we analyzed 15 carbohydrates in the leaves of nine regular-bearing and eight strongly biennial-bearing apple cultivars and found no clear connections between carbohydrates in leaves and bearing behavior of these cultivars. Our data therefore do not support the hypothesis that carbohydrate competition between fruits and buds is the primary trigger of biennial bearing in apple.

Plants are constantly exposed to fluctuating environmental cues. Abiotic stresses such as drought, salinity, and nutrient deficiency often occur simultaneously, severely compromise crop productivity. Abscisic acid (ABA) plays a central role in plant stress signaling, whereas nitrogen -primarily in the forms of nitrate (NO) and ammonium (NH) - is indispensable for plant growth and reproduction. Increasing evidence indicates extensive crosstalk between stress and nutrient signaling pathways. Here, we emphasize the synergistic action of the ABA-mediated signaling pathway and NRT1.1B in enabling plants to fine-tune sophisticated, stress-specific responses. The nitrogen sensing components NRT1.1B and NIN-like protein (NLP) transcription factors act as potential hubs connecting nutrient signaling to ABA-mediated stress signaling. These nitrate signaling components may functionally interact with ABA-mediated stress signaling via the activity of SNF1-related protein kinase 2 (SnRK2) or calcium-signaling kinases. Elucidating these integrative mechanisms provides new insights into nutrient-stress crosstalk and offers potential strategies for engineering crops with enhanced resilience under combined environmental challenges.