Uncovering DELLA-Independent Gibberellin Responses by Characterizing New Tomato procera Mutants

The hormone regulatory mechanism underlying parthenocarpic fruit formation in tomato

Parthenocarpic fruits, known for their superior taste and reliable yields in adverse conditions, develop without the need for fertilization or pollination. Exploring the physiological and molecular mechanisms behind parthenocarpic fruit development holds both theoretical and practical significance, making it a crucial area of study. This review examines how plant hormones and MADS-box transcription factors control parthenocarpic fruit formation. It delves into various aspects of plant hormones-including auxin, gibberellic acid, cytokinins, ethylene, and abscisic acid-ranging from external application to biosynthesis, metabolism, signaling pathways, and their interplay in influencing parthenocarpic fruit development. The review also explores the involvement of MADS family gene functions in these processes. Lastly, we highlight existing knowledge gaps and propose directions for future research on parthenocarpy.

Morphological Changes to Fruit Development Induced by GA3 Application in Sweet Cherry (Prunus avium L.)

Cherry (Prunus avium) fruits are important sources of vitamins, minerals, and nutrients in the human diet; however, they contain a large stone, making them inconvenient to eat 'on the move' and process. The exogenous application of gibberellic acid (GA3) can induce parthenocarpy in a variety of fruits during development. Here, we showed that the application of GA3 to sweet cherry unpollinated pistils acted as a trigger for fruit set and permitted the normal formation of fruit up to a period of twenty-eight days, indicating that gibberellins are involved in the activation of the cell cycle in the ovary wall cells, leading to fruit initiation. However, after this period, fruit development ceased and developing fruit began to be excised from the branch by 35 days post treatment. This work also showed that additional signals are required for the continued development of fully mature parthenocarpic fruit in sweet cherry.

Parthenocarpy, a pollination-independent fruit set mechanism to ensure yield stability

Fruit development is essential for flowering plants' reproduction and a significant food source. Climate change threatens fruit yields due to its impact on pollination and fertilization processes, especially vulnerable to extreme temperatures, insufficient light, and pollinator decline. Parthenocarpy, the development of fruit without fertilization, offers a solution, ensuring yield stability in adverse conditions and enhancing fruit quality. Parthenocarpic fruits not only secure agricultural production but also exhibit improved texture, appearance, and shelf life, making them desirable for food processing and other applications. Recent research unveils the molecular mechanisms behind parthenocarpy, implicating transcription factors (TFs), noncoding RNAs, and phytohormones such as auxin, gibberellin (GA), and cytokinin (CK). Here we review recent findings, construct regulatory models, and identify areas for further research.

Identification and characterization of CsERECTA, a major gene controlling stem elongation through regulating GA biosynthesis in cucumber

Dwarfing is an ideal agronomic trait in crop breeding, which can improve lodging resistance and increase crop productivity. In this study, we identified a dwarf mutant cp-3 from an EMS-mutagenized population, which had extremely short internodes, and the cell length and number of internodes were significantly reduced. Meanwhile, exogenous GA3 treatment partially rescued the plant height of the cp-3. Inheritance analysis showed that the cp-3 mutant was regulated via a recessive nuclear locus. A candidate gene, CsERECTA, encoding an LRR receptor-like serine/threonine-protein kinase, was cloned through a map-based cloning strategy. Sequence analysis showed that a nucleotide mutation (C ~ T) in exon 26 of CsERECTA led to premature termination of the protein. Subsequently, two transgenic lines were generated using the CRISPR/Cas9 system, and they showed plant dwarfing. Plant endogenous hormones quantitative and RNA-sequencing analysis revealed that GA3 content and the expression levels of genes related to GA biosynthesis were significantly reduced in Cser knockout mutants. Meanwhile, exogenous GA3 treatment partially rescued the dwarf phenotype of Cser knockout mutants. These findings revealed that CsERECTA controls stem elongation by regulating GA biosynthesis in cucumber.

Cloning and functional mechanism of the dwarf gene gba affecting stem elongation and cellulose biosynthesis in jute (Corchorus olitorius)

Plant height (PH) is an important factor affecting bast fiber yield in jute. Here, we report the mechanism of dwarfism in the 'Guangbaai' (gba) of jute. The mutant gba had shorter internode length and cell length compared to the standard cultivar 'TaiZi 4' (TZ4). Exogenous GA3 treatment indicated that gba is a GA-insensitive dwarf mutant. Quantitative trait locus (QTL) analysis of three PH-related traits via a high-density genetic linkage map according to re-seq showed that a total of 25 QTLs were identified, including 13 QTLs for PH, with phenotypic variation explained ranging from 2.42 to 74.16%. Notably, the functional mechanism of the candidate gene CoGID1a, the gibberellic acid receptor, of the major locus qPHIL5 was evaluated by transgenic analysis and virus-induced gene silencing. A dwarf phenotype-related single nucleotide mutation in CoGID1a was identified in gba, which was also unique to the dwarf phenotype of gba among 57 cultivars. Cogid1a was unable to interact with the growth-repressor DELLA even in the presence of highly accumulated gibberellins in gba. Differentially expressed genes between transcriptomes of gba and TZ4 after GA3 treatment indicated up-regulation of genes involved in gibberellin and cellulose synthesis in gba. Interestingly, it was found that up-regulation of CoMYB46, a key transcription factor in the secondary cell wall, by the highly accumulated gibberellins in gba promoted the expression of cellulose synthase genes CoCesA4 and CoCesA7. These findings provide valuable insights into fiber development affected by endogenous gibberellin accumulation in plants.

The tomato EAR-motif repressor, SlERF36, accelerates growth transitions and reduces plant life cycle by regulating GA levels and responses

Faster vegetative growth and early maturity/harvest reduce plant life cycle time and are important agricultural traits facilitating early crop rotation. GA is a key hormone governing developmental transitions that determine growth speed in plants. An EAR-motif repressor, SlERF36 that regulates various growth transitions, partly through regulation of the GA pathway and GA levels, was identified in tomato. Suppression of SlERF36 delayed germination, slowed down organ growth and delayed the onset of flowering time, fruit harvest and whole-plant senescence by 10-15 days. Its over-expression promoted faster growth by accelerating all these transitions besides increasing organ expansion and plant height substantially. The plant life cycle and fruit harvest were completed 20-30 days earlier than control without affecting yield, in glasshouse as well as net-house conditions, across seasons and generations. These changes in life cycle were associated with reciprocal changes in expression of GA pathway genes and basal GA levels between suppression and over-expression lines. SlERF36 interacted with the promoters of two GA2 oxidase genes, SlGA2ox3 and SlGA2ox4, and the DELLA gene, SlDELLA, reducing their transcription and causing a 3-5-fold increase in basal GA3/GA4 levels. Its suppression increased SlGA2ox3/4 transcript levels and reduced GA3/GA4 levels by 30%-50%. SlERF36 is conserved across families making it an important candidate in agricultural and horticultural crops for manipulation of plant growth and developmental transitions to reduce life cycles for faster harvest.

TOR coordinates cytokinin and gibberellin signals mediating development and defense

Plants constantly perceive and process environmental signals and balance between the energetic demands of growth and defense. Growth arrest upon pathogen attack was previously suggested to result from a redirection of the plants' metabolic resources towards the activation of plant defense. The energy sensor Target of Rapamycin (TOR) kinase is a conserved master coordinator of growth and development in all eukaryotes. Although TOR is positioned at the interface between development and defense, little is known about the mechanisms by which TOR may potentially regulate the relationship between these two modalities. The plant hormones cytokinin (CK) and gibberellin (GA) execute various aspects of plant development and defense. The ratio between CK and GA was reported to determine the outcome of developmental programmes. Here, investigating the interplay between TOR-mediated development and TOR-mediated defense in tomato, we found that TOR silencing resulted in rescue of several different aberrant developmental phenotypes, demonstrating that TOR is required for the execution of developmental cues. In parallel, TOR inhibition enhanced immunity in genotypes with a low CK/GA ratio but not in genotypes with a high CK/GA ratio. TOR-inhibition mediated disease resistance was found to depend on developmental status, and was abolished in strongly morphogenetic leaves, while being strongest in mature, differentiated leaves. CK repressed TOR activity, suggesting that CK-mediated immunity may rely on TOR downregulation. At the same time, TOR activity was promoted by GA, and TOR silencing reduced GA sensitivity, indicating that GA signalling requires normal TOR activity. Our results demonstrate that TOR likely acts in concert with CK and GA signalling, executing signalling cues in both defense and development. Thus, differential regulation of TOR or TOR-mediated processes could regulate the required outcome of development-defense prioritisation.

The R2R3-MYB transcription factor EVER controls the emission of petunia floral volatiles by regulating epicuticular wax biosynthesis in the petal epidermis

The epidermal cells of petunia (Petunia × hybrida) flowers are the main site of volatile emission. However, the mechanisms underlying the release of volatiles into the environment are still being explored. Here, using cell-layer-specific transcriptomic analysis, reverse genetics by virus-induced gene silencing and clustered regularly interspaced short palindromic repeat (CRISPR), and metabolomics, we identified EPIDERMIS VOLATILE EMISSION REGULATOR (EVER)-a petal adaxial epidermis-specific MYB activator that affects the emission of volatiles. To generate ever knockout lines, we developed a viral-based CRISPR/Cas9 system for efficient gene editing in plants. These knockout lines, together with transient-suppression assays, revealed EVER's involvement in the repression of low-vapor-pressure volatiles. Internal pools and annotated scent-related genes involved in volatile production and emission were not affected by EVER. RNA-Seq analyses of petals of ever knockout lines and EVER-overexpressing flowers revealed enrichment in wax-related biosynthesis genes. Liquid chromatography/gas chromatography-MS analyses of petal epicuticular waxes revealed substantial reductions in wax loads in ever petals, particularly of monomers of fatty acids and wax esters. These results implicate EVER in the emission of volatiles by fine-tuning the composition of petal epicuticular waxes. We reveal a petunia MYB regulator that interlinks epicuticular wax composition and volatile emission, thus unraveling a regulatory layer in the scent-emission machinery in petunia flowers.

Seed Longevity and Ageing: A Review on Physiological and Genetic Factors with an Emphasis on Hormonal Regulation

Upon storage, seeds inevitably age and lose their viability over time, which determines their longevity. Longevity correlates with successful seed germination and enhancing this trait is of fundamental importance for long-term seed storage (germplasm conservation) and crop improvement. Seed longevity is governed by a complex interplay between genetic factors and environmental conditions experienced during seed development and after-ripening that will shape seed physiology. Several factors have been associated with seed ageing such as oxidative stress responses, DNA repair enzymes, and composition of seed layers. Phytohormones, mainly abscisic acid, auxins, and gibberellins, have also emerged as prominent endogenous regulators of seed longevity, and their study has provided new regulators of longevity. Gaining a thorough understanding of how hormonal signalling genes and pathways are integrated with downstream mechanisms related to seed longevity is essential for formulating strategies aimed at preserving seed quality and viability. A relevant aspect related to research in seed longevity is the existence of significant differences between results depending on the seed equilibrium relative humidity conditions used to study seed ageing. Hence, this review delves into the genetic, environmental and experimental factors affecting seed ageing and longevity, with a particular focus on their hormonal regulation. We also provide gene network models underlying hormone signalling aimed to help visualize their integration into seed longevity and ageing. We believe that the format used to present the information bolsters its value as a resource to support seed longevity research for seed conservation and crop improvement.

Identification of flowering genes in Camellia perpetua by comparative transcriptome analysis

Camellia perpetua has the excellent characteristic of flowering multiple times throughout the year, which is of great importance to solve the problem of "short flowering period" and "low fresh flower yield" in the yellow Camellia industry at present. Observations of flowering phenology have demonstrated that most floral buds of C. perpetua were formed by the differentiation of axillary buds in the scales at the base of the terminal buds of annual branches. However, the molecular mechanism of flowering in C. perpetua is still unclear. In this study, we conducted a comparative transcriptomic study of the terminal buds and their basal flower buds in March (spring) and September (autumn) using RNA-seq and found that a total of 11,067 genes were significantly differentially expressed in these two periods. We identified 27 genes related to gibberellin acid (GA) synthesis, catabolism, and signal transduction during floral bud differentiation. However, treatment of the terminal buds and axillary buds of C. perpetua on annual branch with GA3 did not induce floral buds at the reproductive growth season (in August) but promoted shoot sprouting. Moreover, 203 flowering genes were identified from the C. perpetua transcriptome library through homology alignment, including flowering integrators LEAFY (LFY) and UNUSUAL FLORAL ORGANS (UFO), as well as MADS-box, SQUAMOSA PROMOTER BINDING PROTEIN-box (SBP-box), and TEOSINTE BRANCHED1/CYCLOIDEA/PROLIFERATING CELL FACTOR (TCP) genes, which were specifically upregulated in floral buds and were likely involved in flowering in C. perpetua. The floral inhibitor CperTFL1b was identified and cloned from C. perpetua, and its expression level was specifically regulated in terminal buds in autumn. Ectopic overexpression of CperTFL1b delayed flowering time and produced abnormal inflorescence and floral organs in Arabidopsis, suggesting that CperTFL1b inhibits flowering. In conclusion, this study deepens our understanding of the molecular mechanism of blooms throughout the year in C. perpetua and provides a helpful reference for cultivating new varieties of yellow Camellia with improved flowering traits.

Immunity priming uncouples the growth-defense trade-off in tomato

Plants have developed an array of mechanisms to protect themselves against pathogen invasion. The deployment of defense mechanisms is imperative for plant survival, but can come at the expense of plant growth, leading to the 'growth-defense trade-off' phenomenon. Following pathogen exposure, plants can develop resistance to further attack. This is known as induced resistance, or priming. Here, we investigated the growth-defense trade-off, examining how defense priming via systemic acquired resistance (SAR), or induced systemic resistance (ISR), affects tomato development and growth. We found that defense priming can promote, rather than inhibit, plant development, and that defense priming and growth trade-offs can be uncoupled. Cytokinin response was activated during induced resistance, and found to be required for the observed growth and disease resistance resulting from ISR activation. ISR was found to have a stronger effect than SAR on plant development. Our results suggest that growth promotion and induced resistance can be co-dependent, and that, in certain cases, defense priming can drive developmental processes and promote plant yield.

Coordination of growth and drought responses by GA-ABA signaling in rice

The drought caused by global warming seriously affects the crop growth and agricultural production. Plants have evolved distinct strategies to cope with the drought environment. Under drought stress, energy and resources should be diverted from growth toward stress management. However, the molecular mechanism underlying coordination of growth and drought response remains largely elusive. Here, we discovered that most of the gibberellin (GA) metabolic genes were regulated by water scarcity in rice, leading to the lower GA contents and hence inhibited plant growth. Low GA contents resulted in the accumulation of more GA signaling negative regulator SLENDER RICE 1, which inhibited the degradation of abscisic acid (ABA) receptor PYL10 by competitively binding to the co-activator of anaphase-promoting complex TAD1, resulting in the enhanced ABA response and drought tolerance. These results elucidate the synergistic regulation of crop growth inhibition and promotion of drought tolerance and survival, and provide useful genetic resource in breeding improvement of crop drought resistance.

Gibberellin and miRNA156-targeted SlSBP genes synergistically regulate tomato floral meristem determinacy and ovary patterning

Many developmental processes associated with fruit development occur at the floral meristem (FM). Age-regulated microRNA156 (miR156) and gibberellins (GAs) interact to control flowering time, but their interplay in subsequent stages of reproductive development is poorly understood. Here, in tomato (Solanum lycopersicum), we show that GA and miR156-targeted SQUAMOSA PROMOTER-BINDING PROTEIN-LIKE (SPL or SBP) genes interact in the tomato FM and ovary patterning. High GA responses or overexpression of miR156 (156OE), which leads to low expression levels of miR156-silenced SBP genes, resulted in enlarged FMs, ovary indeterminacy and fruits with increased locule number. Conversely, low GA responses reduced indeterminacy and locule number, and overexpression of a S. lycopersicum (Sl)SBP15 allele that is miR156 resistant (rSBP15) reduced FM size and locule number. GA responses were partially required for the defects observed in 156OE and rSBP15 fruits. Transcriptome analysis and genetic interactions revealed shared and divergent functions of miR156-targeted SlSBP genes, PROCERA/DELLA and the classical WUSCHEL/CLAVATA pathway, which has been previously associated with meristem size and determinacy. Our findings reveal that the miR156/SlSBP/GA regulatory module is deployed differently depending on developmental stage and create novel opportunities to fine-tune aspects of fruit development that have been important for tomato domestication.

Molecular, hormonal, and metabolic mechanisms of fruit set, the ovary-to-fruit transition, in horticultural crops

Fruit set is the process by which the ovary develops into a fruit and is an important factor in determining fruit yield. Fruit set is induced by two hormones, auxin and gibberellin, and the activation of their signaling pathways, partly by suppressing various negative regulators. Many studies have investigated the structural changes and gene networks in the ovary during fruit set, revealing the cytological and molecular mechanisms. In tomato (Solanum lycopersicum), SlIAA9 and SlDELLA/PROCERA act as auxin and gibberellin signaling repressors, respectively, and are important regulators of the activity of transcription factors and downstream gene expression involved in fruit set. Upon pollination, SlIAA9 and SlDELLA are degraded, which subsequently activates downstream cascades and mainly contributes to active cell division and cell elongation, respectively, in ovaries during fruit setting. According to current knowledge, the gibberellin pathway functions as the most downstream signal in fruit set induction, and therefore its role in fruit set has been extensively explored. Furthermore, multi-omics analysis has revealed the detailed dynamics of gene expression and metabolites downstream of gibberellins, highlighting the rapid activation of central carbon metabolism. This review will outline the relevant mechanisms at the molecular and metabolic levels during fruit set, particularly focusing on tomato.

Interaction of VvDELLA2 and VvCEB1 Mediates Expression of Expansion-Related Gene during GA-Induced Enlargement of Grape Fruit

Exogenous gibberellin treatment can promote early growth of grape fruit, but the underlying regulatory mechanisms are not well understood. Here, we show that VvDELLA2 directly regulates the activity of the VvCEB1 transcription factor, a key regulator in the control of cell expansion in grape fruit. Our results show that VvCEB1 binds directly to the promoters of cell expansion-related genes in grape fruit and acts as a transcriptional activator, while VvDELLA2 blocks VvCEB1 function by binding to its activating structural domain. The exogenous gibberellin treatment relieved this inhibition by promoting the degradation of VvDELLA2 protein, thus, allowing VvCEB1 to transcriptionally activate the expression of cell expansion-related genes. In conclusion, we conclude that exogenous GA3 treatment regulates early fruit expansion by affecting the VvDELLA-VvCEB1 interaction in grape fruit development.

The E3 ubiquitin ligases SINA1 and SINA2 integrate with the protein kinase CIPK20 to regulate the stability of RGL2a, a positive regulator of anthocyanin biosynthesis

Although DELLA protein destabilization mediated by post-translational modifications is essential for gibberellin (GA) signal transduction and GA-regulated anthocyanin biosynthesis, the related mechanisms remain largely unknown. In this study, we report the ubiquitination and phosphorylation of an apple DELLA protein MdRGL2a in response to GA signaling and its regulatory role in anthocyanin biosynthesis. MdRGL2a could interact with MdWRKY75 to enhance the MdWRKY75-activated transcription of anthocyanin activator MdMYB1 and interfere with the interaction between anthocyanin repressor MdMYB308 and MdbHLH3 or MdbHLH33, thereby promoting anthocyanin accumulation. A protein kinase MdCIPK20 was found to phosphorylate and protect MdRGL2a from degradation, and it was essential for MdRGL2a-promoting anthocyanin accumulation. However, MdRGL2a and MdCIPK20 were ubiquitinated and degraded by E3 ubiquitin ligases MdSINA1 and MdSINA2, respectively, both of which were activated in the presence of GA. Our results display the integration of SINA1/2 with CIPK20 to dynamically regulate GA signaling and will be helpful toward understanding the mechanism of GA signal transduction and GA-inhibited anthocyanin biosynthesis. The discovery of extensive interactions between DELLA and SINA and CIPK proteins in apple will provide reference for the study of ubiquitination and phosphorylation of DELLA proteins in other species.

Comparative transcriptome analysis reveals the function of SlPRE2 in multiple phytohormones biosynthesis, signal transduction and stomatal development in tomato

KEY MESSAGE

Transcriptomic, physiological, and qRT-PCR analysis revealed the potential mechanism by which SlPRE2 regulates plant growth and stomatal size via multiple phytohormone pathways in tomato. Paclobutrazol resistance proteins (PREs) are atypical members of the basic/helix-loop-helix (bHLH) transcription factor family that regulate plant morphology, cell size, pigment metabolism and abiotic stress in response to different phytohormones. However, little is known about the network regulatory mechanisms of PREs in plant growth and development in tomato. In this study, the function and mechanism of SlPRE2 in tomato plant growth and development were investigated. The quantitative RT-PCR results showed that the expression of SlPRE2 was regulated by multiple phytohormones and abiotic stresses. It showed light-repressed expression during the photoperiod. The RNA-seq results revealed that SlPRE2 regulated many genes involved in photosynthesis, chlorophyll metabolism, phytohormone metabolism and signaling, and carbohydrate metabolism, suggesting the role of SlPRE2 in gibberellin, brassinosteroid, auxin, cytokinin, abscisic acid and salicylic acid regulated plant development processes. Moreover, SlPRE2 overexpression plants showed widely opened stomata in young leaves, and four genes involved in stomatal development showed altered expression. Overall, the results demonstrated the mechanism by which SlPRE2 regulates phytohormone and stress responses and revealed the function of SlPRE2 in stomatal development in tomato. These findings provide useful clues for understanding the molecular mechanisms of SlPRE2-regulated plant growth and development in tomato.

DELLA functions evolved by rewiring of associated transcriptional networks

DELLA proteins are land-plant specific transcriptional regulators that transduce environmental information to multiple processes throughout a plant's life^1-3. The molecular basis for this critical function in angiosperms has been linked to the regulation of DELLA stability by gibberellins and to the capacity of DELLA proteins to interact with hundreds of transcription factors^4,5. Although bryophyte orthologues can partially fulfil functions attributed to angiosperm DELLA^6,7, it is not clear whether the capacity to establish interaction networks is an ancestral property of DELLA proteins or is associated with their role in gibberellin signalling^8-10. Here we show that representative DELLAs from the main plant lineages display a conserved ability to interact with multiple transcription factors. We propose that promiscuity was encoded in the ancestral DELLA protein, and that this property has been largely maintained, whereas the lineage-dependent diversification of DELLA-dependent functions mostly reflects the functional evolution of their interacting partners.

CRYPTOCHROME 1a-mediated blue light perception regulates tomato seed germination via changes in hormonal balance and endosperm-degrading hydrolase dynamics

Blue light exposure delays tomato seed germination by decreasing endosperm-degrading hydrolase activities, a process regulated by CRY1a-dependent signaling and the hormonal balance between ABA and GA. The germination of tomato seeds (Solanum lycopersicum L.) is tightly controlled by an internal hormonal balance, which is also influenced by environmental factors such as light. In this study, we investigated the blue light (BL)-mediated impacts on physiological, biochemical, and molecular processes during the germination of the blue light photoreceptor CRYPTOCHROME 1a loss-of-function mutant (cry1a) and of the hormonal tomato mutants notabilis (not, deficient in ABA) and procera (pro, displaying a GA-constitutive response). Seeds were germinated in a controlled chamber in the dark and under different intensities of continuous BL (ranging from 1 to 25 µmol m^-2 s^-1). In general, exposure to BL delayed tomato seed germination in a fluency rate-dependent way due to negative impacts on the activities of endosperm-degrading hydrolases, such as endo-β-mannanase, β-mannosidase, and α-galactosidase. However, not and pro mutants presented higher germination speed index (GSI) compared to WT despite the BL influence, associated with higher hydrolase activities, especially evident in pro, indicating that the ABA/GA hormonal balance is important to diminish BL inhibition over tomato germination. The cry1a germination percentage was higher than in WT in the dark but its GSI was lower under BL exposure, suggesting that functional CRY1a is required for BL-dependent germination. BL inhibits the expression of GA-biosynthetic genes, and induces GA-deactivating and ABA-biosynthetic genes. The magnitude of the BL influence over the hormone-related transcriptional profile is also dependent upon CRY1a, highlighting the complex interplay between light and hormonal pathways. These results contribute to a better understanding of BL-induced events behind the photoregulation of tomato seed germination.

How Changes in ABA Accumulation and Signaling Influence Tomato Drought Responses and Reproductive Development

Water deficit conditions trigger the production of a chemical signal, the phytohormone abscisic acid (ABA), which coordinates multiple responses at different temporal and spatial scales. Despite the complexity of natural drought conditions, the modulation of ABA signaling could be harnessed to ameliorate the drought performances of crops in the face of increasingly challenging climate conditions. Based on recent studies, increasing ABA sensitivity can lead to genotypes with improved drought resistance traits, with sustained biomass production in water-limiting environments and little or no costs with respect to biomass production under optimal conditions. However, variations in ABA production and sensitivity lead to changes in various aspects of reproductive development, including flowering time. Here we provide an updated summary of the literature on ABA-related genes in tomato and discuss how their manipulation can impact water-deficit-related responses and/or other developmental traits. We suggest that a better understanding of specific ABA components’ function or their expression may offer novel tools to specifically engineer drought resistance without affecting developmental traits.

Ultrastructure change and transcriptome analysis of GA3 treatment on seed germination of moso bamboo(Phyllostachys edulis)

Exploring the mechanism of Gibberellic acid (GA₃) treatment on seed germination of moso bamboo can lay a foundation for its future breeding and research. In this study, the germination-related indicators (germination rate, germination potential, vigor index, respiration rate) with different content of GA₃ treatment were measured, and the ultrastructure of moso bamboo seeds treated with low and high GA₃ concentrations was observed during the germination process. In addition, the transcriptome data of the germination seeds, with and without GA₃ treatment were analyzed. The results showed that the low GA₃ concentration (10 mol/L) increased the germination rate, germination potential, vigor index and respiration rate, thus promoting the germination of moso bamboo seeds, but a high concentration of GA₃ (50 mol/L) inhibited the seed germination. The low GA₃ concentration accelerated the decomposition of starch and fat and promoted the vacuole formation of cells, but the high GA₃ concentration damaged organelles and increased the endocytosis of cells. Compared with untreated moso bamboo seeds, the seeds had fewer genes expressed after GA₃ treatment. Starch and carbon metabolism play a very important role in seed development and embryo viability, whether the seed is treated with GA₃ or not. After hormone treatment, GID1 and DELLA-related genes homologous to rice genes is not expressed, but the expression of PIF4, PIF5, GA₃ox2, GA₂oxs, etc., were up-regulated.

Engineering Abiotic Stress Tolerance in Crop Plants through CRISPR Genome Editing

Environmental abiotic stresses challenge food security by depressing crop yields often exceeding 50% of their annual production. Different methods, including conventional as well as genomic-assisted breeding, mutagenesis, and genetic engineering have been utilized to enhance stress resilience in several crop species. Plant breeding has been partly successful in developing crop varieties against abiotic stresses owning to the complex genetics of the traits as well as the narrow genetic base in the germplasm. Irrespective of the fact that genetic engineering can transfer gene(s) from any organism(s), transgenic crops have become controversial mainly due to the potential risk of transgene-outcrossing. Consequently, the cultivation of transgenic crops is banned in certain countries, particularly in European countries. In this scenario, the discovery of the CRISPR tool provides a platform for producing transgene-free genetically edited plants-similar to the mutagenized crops that are not extensively regulated such as genetically modified organisms (GMOs). Thus, the genome-edited plants without a transgene would likely go into the field without any restriction. Here, we focused on the deployment of CRISPR for the successful development of abiotic stress-tolerant crop plants for sustaining crop productivity under changing environments.

Options for the generation of seedless cherry, the ultimate snacking product

This manuscript identifies cherry orthologues of genes implicated in the development of pericarpic fruit and pinpoints potential options and restrictions in the use of these targets for commercial exploitation of parthenocarpic cherry fruit. Cherry fruit contain a large stone and seed, making processing of the fruit laborious and consumption by the consumer challenging, inconvenient to eat 'on the move' and potentially dangerous for children. Availability of fruit lacking the stone and seed would be potentially transformative for the cherry industry, since such fruit would be easier to process and would increase consumer demand because of the potential reduction in costs. This review will explore the background of seedless fruit, in the context of the ambition to produce the first seedless cherry, carry out an in-depth analysis of the current literature around parthenocarpy in fruit, and discuss the available technology and potential for producing seedless cherry fruit as an 'ultimate snacking product' for the twenty-first century.

CRISPR/Cas9 Technique for Temperature, Drought, and Salinity Stress Responses

Global warming and climate change have severely affected plant growth and food production. Therefore, minimizing these effects is required for sustainable crop yields. Understanding the molecular mechanisms in response to abiotic stresses and improving agricultural traits to make crops tolerant to abiotic stresses have been going on unceasingly. To generate desirable varieties of crops, traditional and molecular breeding techniques have been tried, but both approaches are time-consuming. Clustered regularly interspaced short palindromic repeat/Cas9 (CRISPR/Cas9) and transcription activator-like effector nucleases (TALENs) are genome-editing technologies that have recently attracted the attention of plant breeders for genetic modification. These technologies are powerful tools in the basic and applied sciences for understanding gene function, as well as in the field of crop breeding. In this review, we focus on the application of genome-editing systems in plants to understand gene function in response to abiotic stresses and to improve tolerance to abiotic stresses, such as temperature, drought, and salinity stresses.

ScGAIL, a sugarcane N-terminal truncated DELLA-like protein, participates in gibberellin signaling in Arabidopsis

The hormone gibberellin (GA) is crucial for internode elongation in sugarcane. DELLA proteins are critical negative regulators of the GA signaling pathway. ScGAI encodes a DELLA protein that was previously implicated in the regulation of sugarcane culm development. Here, we characterized ScGAI-like (ScGAIL) in sugarcane, which lacked the N-terminal region but was otherwise homologous to ScGAI. ScGAIL differed from ScGAI in its chromosomal location, expression patterns, and cellular localization. Although transgenic Arabidopsis overexpressing ScGAIL were insensitive to GAs, GA synthesis was affected in these plants, suggesting that ScGAIL disrupted the GA signaling pathway. After GA treatment, the expression patterns of GA-associated genes differed between ScGAIL-overexpressing and wild-type Arabidopsis, and the degradation of AtDELLA proteins in transgenic lines was significantly inhibited compared with wild-type lines. A sugarcane GID1 gene (ScGID1) encoding a putative GA receptor was isolated and interacted with ScGAIL in a GA-independent manner. Five ScGAIL-interacting proteins were verified by yeast two-hybrid assays, and only one interacted with ScGAI. Therefore, ScGAIL may inhibit plant growth by modulating the GA signaling pathway.

Multiple indeterminate domain (IDD)-DELLA1 complexes participate in gibberellin feedback regulation in peach

Peach encodes 14 INDETERMINATE DOMAIN (IDD) transcription factors. PpIDD4, -12 and -13 mediated PpDELLA1 binding to the PpGA20ox1 promoter. Each of these three PpIDD-DELLA1 complexes activated transcription of PpGA20ox1. PpTPR1 and -4 interrupted the interaction of PpIDDs with PpDELLA1. The plant growth regulator gibberellin (GA) plays an important role in the rapid growth of annual shoots in peach. Our previous study showed that the peach cultivar 'FenHuaShouXingTao' (FHSXT), a gibberellic acid receptor (gid1) mutant, accumulates active GAs in annual shoot tips. This mutant enhances GA feedback regulation in peach. The results of this study suggested that the PpIDD-DELLA1 complex is the underlying mechanism of GA feedback regulation in peach. Fourteen IDD genes were identified in peach, and three PpIDDs (PpIDD4, -12 and -13, all from group IV) interacted with PpDELLA1, an important component in GA signaling pathway. Truncation, segmentation and site mutation of the promoter of PpGA20ox1 (a GA biosynthesis gene) showed that all three PpIDD proteins recognized the core motif TTGTC. PpIDD4 and -13 mainly bind to site 3, while PpIDD12 binds to site 5 of the PpGA20ox1 promoter. All three PpIDD-DELLA1 complexes activated the PpGA20ox1 promoter-LUC fusion. These data suggested that PpIDDs bridge PpDELLA1 and the promoter of PpGA20ox1, which then activated the transcription of PpGA20ox1. In addition, PpTPR1 and -4 disrupted the interaction of PpIDDs with PpDELLA1. Our research will be helpful for understanding and possibly modifying the regulation of annual shoot growth and GA biosynthesis.

Transcriptomic, Hormonomic and Metabolomic Analyses Highlighted the Common Modules Related to Photosynthesis, Sugar Metabolism and Cell Division in Parthenocarpic Tomato Fruits during Early Fruit Set

Parthenocarpy, the pollination-independent fruit set, can raise the productivity of the fruit set even under adverse factors during the reproductive phase. The application of plant hormones stimulates parthenocarpy, but artificial hormones incur extra financial and labour costs to farmers and can induce the formation of deformed fruit. This study examines the performance of parthenocarpic mutants having no transcription factors of SlIAA9 and SlTAP3 and sldella that do not have the protein-coding gene, SlDELLA, in tomato (cv. Micro-Tom). At 0 day after the flowering (DAF) stage and DAFs after pollination, the sliaa9 mutant demonstrated increased pistil development compared to the other two mutants and wild type (WT). In contrast to WT and the other mutants, the sliaa9 mutant with pollination efficiently stimulated the build-up of auxin and GAs after flowering. Alterations in both transcript and metabolite profiles existed for WT with and without pollination, while the three mutants without pollination demonstrated the comparable metabolomic status of pollinated WT. Network analysis showed key modules linked to photosynthesis, sugar metabolism and cell proliferation. Equivalent modules were noticed in the famous parthenocarpic cultivars ‘Severianin’, particularly for emasculated samples. Our discovery indicates that controlling the genes and metabolites proffers future breeding policies for tomatoes.

Tomato SlBES1.8 Influences Leaf Morphogenesis by Mediating Gibberellin Metabolism and Signaling

Leaf morphogenetic activity determines its shape diversity. However, our knowledge of the regulatory mechanism in maintaining leaf morphogenetic capacity is still limited. In tomato, gibberellin (GA) negatively regulates leaf complexity by shortening the morphogenetic window. We here report a tomato BRI1-EMS-suppressor 1 transcription factor, SlBES1.8, that promoted the simplification of leaf pattern in a similar manner as GA functions. OE-SlBES1.8 plants exhibited reduced sensibility to exogenous GA3 treatment whereas showed increased sensibility to the application of GA biosynthesis inhibitor, paclobutrazol. In line with the phenotypic observation, the endogenous bioactive GA contents were increased in OE-SlBES1.8 lines, which certainly promoted the degradation of the GA signaling negative regulator, SlDELLA. Moreover, transcriptomic analysis uncovered a set of overlapping genomic targets of SlBES1.8 and GA, and most of them were regulated in the same way. Expression studies showed the repression of SlBES1.8 to the transcriptions of two GA-deactivated genes, SlGA2ox2 and SlGA2ox6, and one GA receptor, SlGID1b-1. Further experiments confirmed the direct regulation of SlBES1.8 to their promoters. On the other hand, SlDELLA physically interacted with SlBES1.8 and further inhibited its transcriptional regulation activity by abolishing SlBES1.8-DNA binding. Conclusively, by mediating GA deactivation and signaling, SlBES1.8 greatly influenced tomato leaf morphogenesis.

Steroidal alkaloids defence metabolism and plant growth are modulated by the joint action of gibberellin and jasmonate signalling

Steroidal glycoalkaloids (SGAs) are protective metabolites constitutively produced by Solanaceae species. Genes and enzymes generating the vast structural diversity of SGAs have been largely identified. Yet, mechanisms of hormone pathways coordinating defence (jasmonate; JA) and growth (gibberellin; GA) controlling SGAs metabolism remain unclear. We used tomato to decipher the hormonal regulation of SGAs metabolism during growth vs defence tradeoff. This was performed by genetic and biochemical characterisation of different JA and GA pathways components, coupled with in vitro experiments to elucidate the crosstalk between these hormone pathways mediating SGAs metabolism. We discovered that reduced active JA results in decreased SGA production, while low levels of GA or its receptor led to elevated SGA accumulation. We showed that MYC1 and MYC2 transcription factors mediate the JA/GA crosstalk by transcriptional activation of SGA biosynthesis and GA catabolism genes. Furthermore, MYC1 and MYC2 transcriptionally regulate the GA signalling suppressor DELLA that by itself interferes in JA-mediated SGA control by modulating MYC activity through protein-protein interaction. Chemical and fungal pathogen treatments reinforced the concept of JA/GA crosstalk during SGA metabolism. These findings revealed the mechanism of JA/GA interplay in SGA biosynthesis to balance the cost of chemical defence with growth.

Modification of tomato breeding traits and plant hormone signaling by target-AID, the genome-editing system inducing efficient nucleotide substitution

Target activation-induced cytidine deaminase (Target-AID), a novel CRISPR/Cas9-based genome-editing tool, confers the base-editing capability on the Cas9 genome-editing system. It involves the fusion of cytidine deaminase (CDA), which catalyzes cytidine (C) to uridine (U) substitutions, to the mutated nickase-type nCas9 or deactivated-type dCas9. To confirm and extend the applicability of the Target-AID genome-editing system in tomatoes (Solanum lycopersicum L.), we transformed the model tomato cultivar "Micro-Tom" and commercial tomato cultivars using this system by targeting SlDELLA, which encodes a negative regulator of the plant phytohormone gibberellic acid (GA) signaling pathway. We confirmed that the nucleotide substitutions were induced by the Target-AID system, and we isolated mutants showing high GA sensitivity in both "Micro-Tom" and the commercial cultivars. Moreover, by successfully applying this system to ETHYLENE RECEPTOR 1 (SlETR1) with single sgRNA targeting, double sgRNA targeting, as well as dual-targeting of both SlETR1 and SlETR2 with a single sgRNA, we demonstrated that the Target-AID genome-editing system is a promising tool for molecular breeding in tomato crops. This study highlights an important aspect of the scientific and agricultural potential of the combinatorial use of the Target-AID and other base-editing systems.

Hormonal interactions underlying parthenocarpic fruit formation in horticultural crops

In some horticultural crops, such as Cucurbitaceae, Solanaceae, and Rosaceae species, fruit set and development can occur without the fertilization of ovules, a process known as parthenocarpy. Parthenocarpy is an important agricultural trait that can not only mitigate fruit yield losses caused by environmental stresses but can also induce the development of seedless fruit, which is a desirable trait for consumers. In the present review, the induction of parthenocarpic fruit by the application of hormones such as auxins (2,4 dichlorophenoxyacetic acid; naphthaleneacetic acid), cytokinins (forchlorfenuron; 6-benzylaminopurine), gibberellic acids, and brassinosteroids is first presented. Then, the molecular mechanisms of parthenocarpic fruit formation, mainly related to plant hormones, are presented. Auxins, gibberellic acids, and cytokinins are categorized as primary players in initiating fruit set. Other hormones, such as ethylene, brassinosteroids, and melatonin, also participate in parthenocarpic fruit formation. Additionally, synergistic and antagonistic crosstalk between these hormones is crucial for deciding the fate of fruit set. Finally, we highlight knowledge gaps and suggest future directions of research on parthenocarpic fruit formation in horticultural crops.

Gibberellin in tomato: metabolism, signaling and role in drought responses

The growth-promoting hormone gibberellin (GA) regulates numerous developmental processes throughout the plant life cycle. It also affects plant response to biotic and abiotic stresses. GA metabolism and signaling in tomato (Solanum lycopersicum) have been studied in the last three decades and major components of the pathways were characterized. These include major biosynthesis and catabolism enzymes and signaling components, such as the three GA receptors GIBBERELLIN INSENSITIVE DWARF 1 (GID1) and DELLA protein PROCERA (PRO), the central response suppressor. The role of these components in tomato plant development and response to the environment have been investigated. Cultivated tomato, similar to many other crop plants, are susceptible to water deficiency. Numerous studies on tomato response to drought have been conducted, including the possible role of GA in tomato drought resistance. Most studies showed that reduced levels or activity of GA improves drought tolerance and drought avoidance. This review aims to provide an overview on GA biosynthesis and signaling in tomato, how drought affects these pathways and how changes in GA activity affect tomato plant response to water deficiency. It also presents the potential of using the GA pathway to generate drought-tolerant tomato plants with improved performance under both irrigation and water-limited conditions.

DELLA-GAF1 complex is involved in tissue-specific expression and gibberellin feedback regulation of GA20ox1 in Arabidopsis

The GAF1 transcription factor is shown to bind to the promoter of the Arabidopsis GA-biosynthetic enzyme GA20ox1 and, in association with DELLA protein, promotes GA20ox1 expression, thereby contributing to its feedback regulation and tissue specificity. Gibberellins (GAs) are phytohormones that promote plant growth and development, including germination, elongation, flowering, and floral development. Homeostasis of endogenous GA levels is controlled by GA feedback regulation. DELLAs are negative regulators of GA signaling that are rapidly degraded in the presence of GAs. DELLAs regulate several target genes, including AtGA20ox2 and AtGA3ox1, encoding the GA-biosynthetic enzymes GA 20-oxidase and GA 3-oxidase, respectively. Previous studies have identified GAI-ASSOCIATED FACTOR 1 (GAF1) as a DELLA interactor, with which DELLAs act as transcriptional coactivators; furthermore, AtGA20ox2, AtGA3ox1, and AtGID1b were identified as target genes of the DELLA-GAF1 complex. Among the five Arabidopsis GA20ox genes, AtGA20ox1 is the most highly expressed gene during vegetative growth; its expression is controlled by GA feedback regulation. Here, we investigated whether AtGA20ox1 is regulated by the DELLA-GAF1 complex. The electrophoretic mobility shift and transactivation assays showed that three GAF1-binding sites exist in the AtGA20ox1 promoter. Using transgenic plants, we further evaluated the contribution of the DELLA-GAF1 complex to GA feedback regulation and tissue-specific expression. Mutations in two GAF1-binding sites obliterated the negative feedback regulation and tissue-specific expression of AtGA20ox1 in transgenic plants. Thus, our results showed that GAF1-binding sites are involved in GA feedback regulation and tissue-specific expression of AtGA20ox1 in Arabidopsis, suggesting that the DELLA-GAF1 complex is involved in both processes.

New insights into gibberellin signaling in regulating plant growth-metabolic coordination

The Green Revolution of the 1960s boosted cereal crop yields in part through widespread adoption of semi-dwarf plant varieties, many of which were later found to have mutations in either gibberellins (GAs) homeostasis or DELLA proteins. GA is essential for plant growth and developmental regulation and plays an important role in improving crop plant architecture for enhanced grain yield under high nitrogen conditions. A complex regulatory network governs the spatially and temporally controlled genes expression through integrative GA signaling in response to multiple endogenous and environmental cues. In this review, we summarize current advances in understanding the molecular mechanisms of DELLA-dependent and DELLA-independent GA signaling pathways and their contributions to plant developmental and metabolic adaptations to changes in nitrogen availability. The progress in molecular understanding of the plant growth-metabolic coordination will facilitate breeding strategies for future sustainable agriculture and a new Green Revolution.

The scarecrow-like transcription factor SlSCL3 regulates volatile terpene biosynthesis and glandular trichome size in tomato (Solanum lycopersicum)

Tomato (Solanum lycopersicum L.) type VI glandular trichomes that occur on the surface of leaves, stems, young fruits and flowers produce and store a blend of volatile monoterpenes and sesquiterpenes. These compounds play important roles in the interaction with pathogens and herbivorous insects. Although the function of terpene synthases in the biosynthesis of volatile terpenes in tomato has been comprehensively investigated, the deciphering of their transcriptional regulation is only just emerging. We selected transcription factors that are over-expressed in trichomes based on existing transcriptome data and silenced them individually by virus-induced gene silencing. Of these, SlSCL3, a scarecrow-like (SCL) subfamily transcription factor, led to a significant decrease in volatile terpene content and expression of the corresponding terpene synthase genes when its transcription level was downregulated. Overexpression of SlSCL3 dramatically increased both the volatile terpene content and glandular trichome size, whereas its homozygous mutants showed reduced terpene biosynthesis. However, its heterozygous mutants also showed a significantly elevated volatile terpene content and enlarged glandular trichomes, similar to the overexpression plants. SlSCL3 modulates the expression of terpene biosynthetic pathway genes by transcriptional activation, but neither direct protein-DNA binding nor interaction with known regulators was observed. Moreover, transcript levels of the endogenous copy of SlSCL3 were decreased in the overexpression plants but increased in the heterozygous and homozygous mutants, suggesting feedback repression of its own promoter. Taken together, our results provide new insights into the role of SlSCL3 in the complex regulation of volatile terpene biosynthesis and glandular trichome development in tomato.

Interaction between the MtDELLA-MtGAF1 Complex and MtARF3 Mediates Transcriptional Control of MtGA3ox1 to Elaborate Leaf Margin Formation in Medicago truncatula

The molecular mechanisms underlying the diversity of leaf shapes have been of great interest to researchers. Leaf shape depends on the pattern of serrations and the degree of indentation of leaf margins. Multiple transcription factors and hormone signaling pathways are involved in this process. In this study, we characterized the developmental roles of SMALL AND SERRATED LEAF (SSL) by analyzing a recessive mutant in the model legume Medicago truncatula. An ortholog of Arabidopsis thaliana GA3-oxidase 1 (GA3ox1), MtGA3ox1/SSL, is required for GA biosynthesis. Loss of function in MtGA3ox1 results in the small plant and lateral organs. The prominent phenotype of the mtga3ox1 mutant is a more pronounced leaf margin, indicating the critical role of GA level in leaf margin formation. Moreover, 35S:MtDELLA2ΔDELLA and 35S:MtARF3 transgenic plants display leaves with a deeply wavy margin, which resembles those of mtga3ox1. Further investigations show that MtGA3ox1 is under the control of MtDELLA1/2/3-MtGAF1 complex-dependent feedback regulation. Further, MtARF3 behaves as a competitive inhibitor of MtDELLA2/3-MtGAF1 complexes to repress the expression of MtGA3ox1 indirectly. These findings suggest that GA feedback regulatory circuits play a fundamental role in leaf margin formation, in which the posttranslational interaction between transcription factors functions as an additional feature.

Gibberellin and auxin signaling genes RGA1 and ARF8 repress accessory fruit initiation in diploid strawberry

Unlike ovary-derived botanical fruits, strawberry (Fragaria x ananassa) is an accessory fruit derived from the receptacle, the stem tip subtending floral organs. Although both botanical and accessory fruits initiate development in response to auxin and gibberellic acid (GA) released from seeds, the downstream auxin and GA signaling mechanisms underlying accessory fruit development are presently unknown. We characterized GA and auxin signaling mutants in wild strawberry (Fragaria vesca) during early stage fruit development. While mutations in FveRGA1 and FveARF8 both led to the development of larger fruit, only mutations in FveRGA1 caused parthenocarpic fruit formation, suggesting FveRGA1 is a key regulator of fruit set. FveRGA1 mediated fertilization-induced GA signaling during accessory fruit initiation by repressing the expression of cell division and expansion genes and showed direct protein-protein interaction with FveARF8. Further, fvearf8 mutant fruits exhibited an enhanced response to auxin or GA application, and the increased response to GA was due to increased expression of FveGID1c coding for a putative GA receptor. The work reveals a crosstalk mechanism between FveARF8 in auxin signaling and FveGID1c in GA signaling. Together, our work provides functional insights into hormone signaling in an accessory fruit, broadens our understanding of fruit initiation in different fruit types, and lays the groundwork for future improvement of strawberry fruit productivity and quality.

Genome-wide identification, characterization and expression analysis of BES1 gene family in tomato

BACKGROUND

As the key regulators in BR signaling, BES1 family genes regulate thousands of target genes involved in various development processes. So far, the functions of BES1 family are poorly understood in tomato, and a comprehensive genomic and expressional analysis is worth to conduct for this family.

RESULTS

Here, nine SlBES1 family members were identified in tomato and classified into five groups based on the conserved motif, gene structure and phylogenetic analysis. Synteny among tomato, Arabidopsis, pepper and rice were further analyzed to obtain insights into evolutionary characteristics. Several cis-elements related to hormone, stress and plant development were exhibited in the promoter regions of SlBES1 family genes. Subcellular localization showed seven members localized both in the nucleus and cytoplasm, implying the presence of dephosphorylated and phosphorylated form of these seven proteins, furthermore, five of them possessed transcription activation activity whereas the left two functioned as transcriptional repressors. Another two members, however, neither localized in the nucleus nor had transactivation activity. Besides, SlBES1.8 showed flower-specific expression while other members expressed ubiquitously in all organs. Moreover, SlBES1 genes exhibited variational expression in response to nine principal plant hormones. Notably, the expression levels of SlBES1 genes presented a dominant downregulated trend in response to stresses.

CONCLUSIONS

In this study, we systematically analyzed the genomic characterization of SlBES1 family, together with the analyses of protein functional features and expression patterns, our results lay a foundation for the functional research of SlBES1 family.

Gene co-expression analysis of tomato seed maturation reveals tissue-specific regulatory networks and hubs associated with the acquisition of desiccation tolerance and seed vigour

BACKGROUND

During maturation seeds acquire several physiological traits to enable them to survive drying and disseminate the species. Few studies have addressed the regulatory networks controlling acquisition of these traits at the tissue level particularly in endospermic seeds such as tomato, which matures in a fully hydrated environment and does not undergo maturation drying. Using temporal RNA-seq analyses of the different seed tissues during maturation, gene network and trait-based correlations were used to explore the transcriptome signatures associated with desiccation tolerance, longevity, germination under water stress and dormancy.

RESULTS

During maturation, 15,173 differentially expressed genes were detected, forming a gene network representing 21 expression modules, with 3 being specific to seed coat and embryo and 5 to the endosperm. A gene-trait significance measure identified a common gene module between endosperm and embryo associated with desiccation tolerance and conserved with non-endospermic seeds. In addition to genes involved in protection such LEA and HSP and ABA response, the module included antioxidant and repair genes. Dormancy was released concomitantly with the increase in longevity throughout fruit ripening until 14 days after the red fruit stage. This was paralleled by an increase in SlDOG1-2 and PROCERA transcripts. The progressive increase in seed vigour was captured by three gene modules, one in common between embryo and endosperm and two tissue-specific. The common module was enriched with genes associated with mRNA processing in chloroplast and mitochondria (including penta- and tetratricopeptide repeat-containing proteins) and post-transcriptional regulation, as well several flowering genes. The embryo-specific module contained homologues of ABI4 and CHOTTO1 as hub genes associated with seed vigour, whereas the endosperm-specific module revealed a diverse set of processes that were related to genome stability, defence against pathogens and ABA/GA response genes.

CONCLUSION

The spatio-temporal co-expression atlas of tomato seed maturation will serve as a valuable resource for the in-depth understanding of the dynamics of gene expression associated with the acquisition of seed vigour at the tissue level.

Bulk RNA-Seq analysis to dissect the regulation of stigma position in tomato

Transcriptomic analysis of tomato genotypes contrasting for stigma position suggests that stigma insertion occurred by the disruption of a process that finds a parallel in Arabidopsis gynoecium development. Domestication of cultivated tomato (Solanum lycopersicum L.) included the transition from allogamy to autogamy that occurred through the loss of self-incompatibilty and the retraction of the stigma within the antheridial cone. Although the inserted stigma is an established phenotype in modern tomatoes, an exserted stigma is still present in several landraces or vintage varieties. Moreover, exsertion of the stigma is a frequent response to high temperature stress and, being a cause of reduced fertility, a trait of increasing importance. Few QTLs for stigma position have been described and only one of the underlying genes identified. To gain insights on genes involved in stigma position in tomato, a bulk RNA sequencing (RNA-Seq) approach was adopted, using two groups of contrasting genotypes. Phenotypic analysis confirmed the extent and the stability of stigma position in the selected genotypes, whereas they were highly heterogeneous for other reproductive and productive traits. The RNA-Seq analysis yielded 801 differentially expressed genes (DEGs), 566 up-regulated and 235 down-regulated in the genotypes with exserted stigma. Validation by quantitative PCR indicated a high reliability of the RNA-Seq data. Up-regulated DEGs were enriched for genes involved in the cell wall metabolism, lipid transport, auxin response and flavonoid biosynthesis. Down-regulated DEGs were enriched for genes involved in translation. Validation of selected genes on pistil tissue of the 26 single genotypes revealed that differences between bulks could both be due to a general trend of the bulk or to the behaviour of single genotypes. Novel candidate genes potentially involved in the control of stigma position in tomato are discussed.

The Current Status of Research on Gibberellin Biosynthesis

Gibberellins are produced by all vascular plants and several fungal and bacterial species that associate with plants as pathogens or symbionts. In the 60 years since the first experiments on the biosynthesis of gibberellic acid in the fungus Fusarium fujikuroi, research on gibberellin biosynthesis has advanced to provide detailed information on the pathways, biosynthetic enzymes and their genes in all three kingdoms, in which the production of the hormones evolved independently. Gibberellins function as hormones in plants, affecting growth and differentiation in organs in which their concentration is very tightly regulated. Current research in plants is focused particularly on the regulation of gibberellin biosynthesis and inactivation by developmental and environmental cues, and there is now considerable information on the molecular mechanisms involved in these processes. There have also been recent advances in understanding gibberellin transport and distribution and their relevance to plant development. This review describes our current understanding of gibberellin metabolism and its regulation, highlighting the more recent advances in this field.

Transcriptomic analysis reveals the GRAS family genes respond to gibberellin in Salvia miltiorrhiza hairy roots

BACKGROUND

Salvia miltiorrhiza is one of the most important traditional Chinese medicinal plants with high medicinal value. Gibberellins are growth-promoting phytohormones that regulate numerous growth and developmental processes in plants. However, their role on the secondary metabolism regulation has not been investigated.

RESULTS

In this study, we found that gibberellic acid (GA) can promote hairy roots growth and increase the contents of tanshinones and phenolic acids. Transcriptomic sequencing revealed that many genes involved in the secondary metabolism pathway were the GA-responsive. After further analysis of GA signaling pathway genes, which their expression profiles have significantly changed, it was found that the GRAS transcription factor family had a significant response to GA. We identified 35 SmGRAS genes in S. miltiorrhiza, which can be divided into 10 subfamilies. Thereafter, members of the same subfamily showed similar conserved motifs and gene structures, suggesting possible conserved functions.

CONCLUSIONS

Most SmGRAS genes were significantly responsive to GA, indicating that they may play an important role in the GA signaling pathway, also participating in the GA regulation of root growth and secondary metabolism in S. miltiorrhiza.

Systematic Analysis of Gibberellin Pathway Components in Medicago truncatula Reveals the Potential Application of Gibberellin in Biomass Improvement

Gibberellins (GAs), a class of phytohormones, act as an essential natural regulator of plant growth and development. Many studies have shown that GA is related to rhizobial infection and nodule organogenesis in legume species. However, thus far, GA metabolism and signaling components are largely unknown in the model legume Medicago truncatula. In this study, a genome-wide analysis of GA metabolism and signaling genes was carried out. In total 29 components, including 8 MtGA20ox genes, 2 MtGA3ox genes, 13 MtGA2ox genes, 3 MtGID1 genes, and 3 MtDELLA genes were identified in M. truncatula genome. Expression profiles revealed that most members of MtGAox, MtGID1, and MtDELLA showed tissue-specific expression patterns. In addition, the GA biosynthesis and deactivation genes displayed a feedback regulation on GA treatment, respectively. Yeast two-hybrid assays showed that all the three MtGID1s interacted with MtDELLA1 and MtDELLA2, suggesting that the MtGID1s are functional GA receptors. More importantly, M. truncatula exhibited increased plant height and biomass by ectopic expression of the MtGA20ox1, suggesting that enhanced GA response has the potential for forage improvement.

Fruit setting rewires central metabolism via gibberellin cascades

Fruit set is the process whereby ovaries develop into fruits after pollination and fertilization. The process is induced by the phytohormone gibberellin (GA) in tomatoes, as determined by the constitutive GA response mutant procera However, the role of GA on the metabolic behavior in fruit-setting ovaries remains largely unknown. This study explored the biochemical mechanisms of fruit set using a network analysis of integrated transcriptome, proteome, metabolome, and enzyme activity data. Our results revealed that fruit set involves the activation of central carbon metabolism, with increased hexoses, hexose phosphates, and downstream metabolites, including intermediates and derivatives of glycolysis, the tricarboxylic acid cycle, and associated organic and amino acids. The network analysis also identified the transcriptional hub gene SlHB15A, that coordinated metabolic activation. Furthermore, a kinetic model of sucrose metabolism predicted that the sucrose cycle had high activity levels in unpollinated ovaries, whereas it was shut down when sugars rapidly accumulated in vacuoles in fruit-setting ovaries, in a time-dependent manner via tonoplastic sugar carriers. Moreover, fruit set at least partly required the activity of fructokinase, which may pull fructose out of the vacuole, and this could feed the downstream pathways. Collectively, our results indicate that GA cascades enhance sink capacities, by up-regulating central metabolic enzyme capacities at both transcriptional and posttranscriptional levels. This leads to increased sucrose uptake and carbon fluxes for the production of the constituents of biomass and energy that are essential for rapid ovary growth during the initiation of fruit set.

The Tomato DELLA Protein PROCERA Promotes Abscisic Acid Responses in Guard Cells by Upregulating an Abscisic Acid Transporter

Plants reduce transpiration through stomatal closure to avoid drought stress. While abscisic acid (ABA) has a central role in the regulation of stomatal closure under water-deficit conditions, we demonstrated in tomato (Solanum lycopersicum) that a gibberellin response inhibitor, the DELLA protein PROCERA (PRO), promotes ABA-induced stomatal closure and gene transcription in guard cells. To study how PRO affects stomatal closure, we performed RNA-sequencing analysis of isolated guard cells and identified the ABA transporters ABA-IMPORTING TRANSPORTER1 1 (AIT1 1) and AIT1 2, also called NITRATE TRANSPORTER1/PTR TRANSPORTER FAMILY4 6 in Arabidopsis (Arabidopsis thaliana), as being upregulated by PRO. Tomato has four AIT1 genes, but only AIT1 1 and AIT1 2 were upregulated by PRO, and only AIT1 1 exhibited high expression in guard cells. Functional analysis of AIT1 1 in yeast (Saccharomyces cerevisiae) confirmed its activity as an ABA transporter, possibly an importer. A clustered regularly interspaced short palindromic repeats-Cas9-derived ait1 1 mutant exhibited an increased transpiration, a larger stomatal aperture, and a reduced stomatal response to ABA. Moreover, ait1 1 suppressed the promoting effects of PRO on ABA-induced stomatal closure and gene expression in guard cells, suggesting that the effects of PRO on stomatal aperture and transpiration are AIT1.1-dependent. Previous studies suggest a negative crosstalk between gibberellin and ABA that is mediated by changes in hormone biosynthesis and signaling. The results of this study suggest this crosstalk is also mediated by changes in hormone transport.

Mutations in the tomato gibberellin receptors suppress xylem proliferation and reduce water loss under water-deficit conditions

Low gibberellin (GA) activity in tomato (Solanum lycopersicum) inhibits leaf expansion and reduces stomatal conductance. This leads to lower transpiration and improved water status under transient drought conditions. Tomato has three GIBBERELLIN-INSENSITIVE DWARF1 (GID1) GA receptors with overlapping activities and high redundancy. We tested whether mutation in a single GID1 reduces transpiration without affecting growth and productivity. CRISPR-Cas9 gid1 mutants were able to maintain higher leaf water content under water-deficit conditions. Moreover, while gid1a exhibited normal growth, it showed reduced whole-plant transpiration and better recovery from dehydration. Mutation in GID1a inhibited xylem vessel proliferation, which led to lower hydraulic conductance. In stronger GA mutants, we also found reduced xylem vessel expansion. These results suggest that low GA activity affects transpiration by multiple mechanisms: it reduces leaf area, promotes stomatal closure, and reduces xylem proliferation and expansion, and as a result, xylem hydraulic conductance. We further examined if gid1a performs better than the control M82 in the field. Under these conditions, the high redundancy of GID1s was lost and gid1a plants were semi-dwarf, but their productivity was not affected. Although gid1a did not perform better under drought conditions in the field, it exhibited a higher harvest index.

The Multifunctional Dioxygenases of Gibberellin Synthesis

Gibberellin (GA) hormones regulate the development of plants and their responses to environmental signals. The final part of GA biosynthesis is catalyzed by multifunctional 2-oxoglutarate-dependent dioxygenases, which are encoded by multigene families. According to their enzymatic properties and physiological functions, GA-oxidases are classified as anabolic or catabolic enzymes. Together they allow complex regulation of the GA biosynthetic pathway, which adapts the specific hormonal needs of a plant during development and interaction with its environment. In this review, we combine recent advances in enzymatic characterization of the multifunctional GA-oxidases, in particular, from cucumber and Arabidopsis that have been most comprehensively investigated.

Potential function of CbuSPL and gene encoding its interacting protein during flowering in Catalpa bungei

BACKGROUND

"Bairihua", a variety of the Catalpa bungei, has a large amount of flowers and a long flowering period which make it an excellent material for flowering researches in trees. SPL is one of the hub genes that regulate both flowering transition and development.

RESULTS

SPL homologues CbuSPL9 was cloned using degenerate primers with RACE. Expression studies during flowering transition in "Bairihua" and ectopic expression in Arabidopsis showed that CbuSPL9 was functional similarly with its Arabidopsis homologues. In the next step, we used Y2H to identify the proteins that could interact with CbuSPL9. HMGA, an architectural transcriptional factor, was identified and cloned for further research. BiFC and BLI showed that CbuSPL9 could form a heterodimer with CbuHMGA in the nucleus. The expression analysis showed that CbuHMGA had a similar expression trend to that of CbuSPL9 during flowering in "Bairihua". Intriguingly, ectopic expression of CbuHMGA in Arabidopsis would lead to aberrant flowers, but did not effect flowering time.

CONCLUSIONS

Our results implied a novel pathway that CbuSPL9 regulated flowering development, but not flowering transition, with the participation of CbuHMGA. Further investments need to be done to verify the details of this pathway.

Downregulation of SlGRAS15 manipulates plant architecture in tomato (Solanum lycopersicum)

GRAS family transcription factors (TF) are involved in multiple biological processes in plants. In recent years among the 54 identified GRAS proteins, only few have been studied functionally in tomato (Solanum lycopersicum). In the present study, a novel and previously uncharacterized member of tomato GRAS transcription factors family SlGRAS15 was isolated and functionally characterized. It was observed that SlGRAS15 preferably expressed in roots, followed by young leaves, stem, and comparatively low transcripts levels were noticed in all other tissues. To explore the SlGRAS15 function in detail, an RNA interference (RNAi) vector targeting SlGRAS15 was constructed and transformed into tomato plants. The transgenic plants carrying SlGRAS15-RNAi displayed pleiotropic phenotypes associated with multiple agronomical traits including reduced plant height and small leaf size with pointed margins, increased node number, lateral shoots, and petiolules length. In addition, transcriptional analysis revealed that silencing SlGRAS15 altered vegetative growth by downregulating gibberellin (GA) biosynthesis genes and stimulating the GA deactivating genes, thus lowering the endogenous GA content in tomato transgenic lines. Moreover, the GA signaling downstream gene (SlGAST1) was downregulated but the negative regulator of GA signaling (SlDELLA) was upregulated by SlGRAS15 silencing. The root and hypocotyl length in SlGRAS15-RNAi lines showed reduced growth under normal conditions (Mock) as compared with the wild type (WT) control plants. Taken together, these findings enhanced our understanding that suppression of SlGRAS15 lead to a series of developmental processes by modulating gibberellin signaling and demonstrate an association between the SlGRAS15 and GA signaling pathway during vegetative growth in tomato.