GA Synthesis Research Articles

Tomato SlARF5 participate in the flower organ initiation process and control plant height

Plant height is a critical agronomic trait closely linked to yield, primarily regulated by Gibberellins (GA) and auxins, which interact in complex ways. However, the mechanism underlying their interactions remain incompletely understood. In this study, we identified a tomato mutant exhibiting significantly reduced plant height. Through gene cloning and bulked segregant analysis (BSA) sequencing, we found that the mutant gene corresponds to the tomato auxin response factor gene SlARF5/MP. Here, we show that overexpression of SlARF5/MP significantly enhances plant height. Additionally, treatment with GA3 restored the plant height of the mutant to wild-type (WT) levels, indicating that GA content is a key factor influencing plant height. We also observed significant upregulation of GA-biosynthesis genes, including GA2-oxidases GA20ox3 and GA20ox4, as well as the GA3 biosynthesis gene GA3ox1, in SlARF5-overexpressing plants. Furthermore, we demonstrated that SlARF5 directly binds to SlGA2ox3, which mediates the conversion of GA3 to inactive GA, therebyregulating its expression. Our findings suggest that SlARF5 modulates GA3 metabolism by regulating GA synthesis genes, ultimately leading to alterations in plant height.

Gibberellins Play an Essential Role in the Bud Growth of Petunia hybrida.

This study delves into the role of gibberellin (GA) in governing plant branch development, a process that remains incompletely understood. Through a combination of exogenous hormone treatment, gene expression analysis, and transgenic phenotype investigations, the impact of GA on petunia's branch development was explored. The results showed that GA3 alone did not directly induce axillary bud germination. However, paclobutrazol (PAC), an inhibitor of GA synthesis, effectively inhibited bud growth. Interestingly, the simultaneous application of GA3 and 6-BA significantly promoted bud growth in both intact and decapitated plants compared to using 6-BA alone. Moreover, this study observed a significant downregulation of GA synthesis genes, including GA20ox1, GA20ox2, GA20ox3, GA3ox1, and CPS1, alongside an upregulation of GA degradation genes such as GA2ox2, GA2ox4, and GA2ox8. The expression of GA signal transduction gene GID1 and GA response factor RGA was found to be upregulated. Notably, the PhGID1 gene, spanning 1029 bp and encoding 342 amino acids, exhibited higher expression in buds and the lowest expression in leaves. The overexpression of PhGID1 in Arabidopsis resulted in a noteworthy rise in the number of branches. This study highlights the crucial role of GA in bud germination and growth and the positive regulatory function of GA signaling in shoot branching processes.

Role of auxin and gibberellin under low light in enhancing saffron corm starch degradation during sprouting

The mechanisms by which low light accelerates starch macromolecules degradation by auxin and gibberellin (GA) in geophytes during sprouting remain largely unknown. This study investigated these mechanisms in saffron, grown under low light (50 μmol m−2 s−1) and optimal light (200 μmol m−2 s−1) during the sprouting phase. Low light reduced starch concentration in corms by 34.0 % and increased significantly sucrose levels in corms, leaves, and leaf sheaths by 19.2 %, 9.8 %, and 134.5 %, respectively. This was associated with a 33.3 % increase in GA3 level and enhanced auxin signaling. Leaves synthesized IAA under low light, which was transported to the corms to promote GA synthesis, facilitating starch degradation through a 228.7 % increase in amylase activity. Exogenous applications of GA and IAA, as well as the use of their synthesis or transport inhibitors, confirmed the synergistic role of these phytohormones in starch metabolism. The unigenes associated with GA biosynthesis and auxin signaling were upregulated under low light, highlighting the IAA-GA module role in starch degradation. Moreover, increased respiration rate and invertase activity, crucial for ATP biosynthesis and the tricarboxylic acid cycle, were consistent with the upregulation of related unigenes, suggesting that auxin signaling accelerates starch degradation by promoting energy metabolism. Upregulated of auxin signaling (CsSAUR32) and starch metabolism (CsSnRK1) genes under low light suggests that auxin directly regulate starch degradation in saffron corms. This study elucidates that low light modulates auxin and GA interactions to accelerate starch degradation in saffron corms during sprouting, offering insights for optimizing agricultural practices under suboptimal light conditions.

Enhanced arsenic stress tolerance in landrace and improved rice cultivars through modulation of gibberellic acid (GA3) synthesis and antioxidant metabolism via phosphorus and silicon supplementation

Arsenic (As), an environmental pollutant, imposes toxic impacts on plant health. In recent years, researchers have focused on comprehending the As-induced intrusion in growth and metabolic components. However, the interactions between phosphorus (P) and silicon (Si) remain elusive, specifically in rice (Oryza sativa) cultivars. Therefore, the present study investigated the effects of P and Si on the defense mechanisms, nutrients accumulation, carbohydrate metabolism, gibberellic acid (GA3) synthesis, and growth responses in Indica rice cultivars (landrace and improved) under As stress. With this focus, our study potentially indicated that As stress (150 µM) negatively impacted the underlying physiological and growth traits, with more pronounced effects on the improved cultivar compared to the landrace. However, P (30 mg kg−1 soil) and/ or Si (1 mM) treatments have prominently reduced oxidative stress with improved defense mechanisms and GA synthesis. Modulation of enzymatic defense system increased in both cultivars but more pronounced in landrace, including superoxide dismutase (+36.47%, +24.43%), ascorbate peroxidase (+95.11%, +78.26%), along with non-enzymatic antioxidants such as ascorbate (+29.43%, +21.48%), and reduced glutathione (+75.45%, +62.34%) concentrations, respectively. Notably, GA concentration (+23.78%, +16.48%) was substantially increased by the cumulative application of P and Si under As stress in both cultivars but more conspicuous in the landrace, respectively. Further, employing GA biosynthesis inhibitor, paclobutrazol (PBZ; 10 µM), substantiated the input of GA-mediated As tolerance, wherein, PBZ reversed the impacts of P and Si on the endogenous GA concentration and defense metabolism. In summation, landrace outperformed improved cultivar leading to As tolerance. This implies that the landrace could be used for future breeding programs permitting in-depth considerations of P and Si-mediated GA3 synthesis under As stress conditions.

Identification of ARF Genes and Elucidation of the Regulatory Effects of PsARF16a on the Dormancy of Tree Peony Plantlets.

The low survival rate of transplanted plantlets, which has limited the utility of tissue-culture-based methods for the rapid propagation of tree peonies, is due to plantlet dormancy after rooting. We previously determined that the auxin response factor PsARF may be a key regulator of tree peony dormancy. To clarify the mechanism mediating tree peony plantlet dormancy, PsARF genes were systematically identified and analyzed. Additionally, PsARF16a was transiently expressed in the leaves of tree peony plantlets to examine its regulatory effects on a downstream gene network. Nineteen PsARF genes were identified and divided into four classes. All PsARF genes encoded proteins with conserved B3 and ARF domains. The number of motifs, exons, and introns varied between PsARF genes in different classes. The overexpression of PsARF16a altered the expression of NCED, ZEP, PYL, GA2ox1, GID1, and other key genes in abscisic acid (ABA) and gibberellin (GA) signal transduction pathways, thereby promoting ABA synthesis and decreasing GA synthesis. Significant changes to the expression of some key genes contributing to starch and sugar metabolism (e.g., AMY2A, BAM3, BGLU, STP, and SUS2) may be associated with the gradual conversion of sugar into starch. This study provides important insights into PsARF functions in tree peonies.

Ascorbic acid releases dormancy and promotes germination by an integrated regulation of abscisic acid and gibberellin in Pyrus betulifolia seeds.

Seed dormancy is an important life history state in which intact viable seeds delay or prevent germination under suitable conditions. Ascorbic acid (AsA) acts as a small molecule antioxidant, and breaking seed dormancy and promoting subsequent growth are among its numerous functions. In this study, a germination test using Pyrus betulifolia seeds treated with exogenous AsA or AsA synthesis inhibitor lycorine (Lyc) and water absorption was conducted. The results indicated that AsA released dormancy and increased germination and 20 mmol L-1 AsA promoted cell division, whereas Lyc reduced germination. Seed germination showed typical three phases of water absorption; and seeds at five key time points were sampled for transcriptome analysis. It revealed that multiple pathways were involved in breaking dormancy and promoting germination through transcriptome data, and 12 differentially expressed genes (DEGs) related to the metabolism and signal transduction of abscisic acid (ABA) and gibberellins (GA) were verified by subsequent RT-qPCR. For metabolites, exogenous AsA increased endogenous AsA and GA3 but reduced ABA and the ABA/GA3 ratio. In addition, three genes regulating ABA synthesis were downregulated by AsA, while five genes mediating ABA degradation were upregulated. Taken together, AsA regulates the pathways associated with ABA and GA synthesis, catalysis, and signal transduction, with subsequent reduction in ABA and increase in GA and further the balance of ABA/GA, ultimately releasing dormancy and promoting germination.

Gibberellin-Mediated Sensitivity of Rice Roots to Aluminum Stress.

Aluminum toxicity poses a significant constraint on crop production in acidic soils. While phytohormones are recognized for their pivotal role in mediating plant responses to aluminum stress, the specific involvement of gibberellin (GA) in regulating aluminum tolerance remains unexplored. In this study, we demonstrate that external GA exacerbates the inhibitory impact of aluminum stress on root growth of rice seedlings, concurrently promoting reactive oxygen species (ROS) accumulation. Furthermore, rice plants overexpressing the GA synthesis gene SD1 exhibit enhanced sensitivity to aluminum stress. In contrast, the slr1 gain-of-function mutant, characterized by impeded GA signaling, displays enhanced tolerance to aluminum stress, suggesting the negative regulatory role of GA in rice resistance to aluminum-induced toxicity. We also reveal that GA application suppresses the expression of crucial aluminum tolerance genes in rice, including Al resistance transcription factor 1 (ART1), Nramp aluminum transporter 1 (OsNramp4), and Sensitive to Aluminum 1 (SAL1). Conversely, the slr1 mutant exhibits up-regulated expression of these genes compared to the wild type. In summary, our results shed light on the inhibitory effect of GA in rice resistance to aluminum stress, contributing to a theoretical foundation for unraveling the intricate mechanisms of plant hormones in regulating aluminum tolerance.

Negotiating soil water deficit in mycorrhizal trifoliate orange plants: A gibberellin pathway

Gibberellins (GAs), an important endogenous hormone, serve a crucial regulatory role in plants’ resistance to environmental stress, whereas it is unclear whether and how arbuscular mycorrhizal fungi (AMF) regulate the profile of GAs in plants exposed to soil water deficit (SWD). This study aimed to analyze how Rhizoglomus intraradices inoculation affected plant growth performance, antioxidant enzyme activities, and the composition, synthesis, metabolism, and signaling pathways of GAs in the roots of trifoliate orange (Poncirus trifoliata) under a 10-week SWD. Although the SWD decreased both root AMF colonization and soil hyphal length, mycorrhizal plants nevertheless outperformed non-mycorrhizal plants in terms of growth performance, as well as peroxidase (70.0%) and catalase (149.2%) activities, indicating greater drought tolerance. A total of nine GAs compositions were detected in the roots, with bioactive GA4 exclusively found in AMF roots. AMF colonization significantly reduced bioactive GA3 levels by 37.9%, while it increased inactive GA8, GA9, and GA15 levels under SWD by 522.2%, 100.0%, and 2500.0%. Inoculation with AMF also up-regulated the expression of PtCPS, PtPKS, and PtKO in GA synthesis pathways of roots and the expression of PtGA20ox, PtGA3ox, and PtGA2ox in GA metabolisms under SWD. In addition, the expression of DELLA genes PtGaipb and PtGai associated with GA signaling pathways was further up-regulated under SWD by AMF inoculation. It is concluded that AMF regulated the composition, synthesis, and deactivation of GAs in roots to promote plant growth, along with an increase in PtGaipb and PtGai expression to possibly initiate mycorrhizal signaling pathways in response to SWD.

Involvement of GA3-oxidase in inhibitory effect of nitric oxide on primary root growth in Arabidopsis.

Both NO and GAs are essential for regulating various physiological processes and stress responses in plants. However, the interaction between these two molecules remains unclear. We investigated the distinct response patterns of Arabidopsis thaliana Col-0 and GA synthesis functional deficiency mutants to NO by measuring root length. To investigate underlying mechanisms, we detected bioactive GA content using UHPLC-ESI-MS/MS, assessed the accumulation of ROS by chemical staining Arabidopsis roots. We also conducted RNA-seq analysis and compared results between Col-0 and ga3ox1, with and without SNP (as NO donor) treatment. Phenotypic results revealed that the inhibitory effect of NO on primary roots of Arabidopsis was primarily mediated by GA3-oxidase, rather than GA20-oxidase or GA2-oxidase. The content of GA3 decreased in Col-0 treated with SNP, whereas this decrease was not observed in ga3ox1. The deficiency of GA3-oxidase alleviated the buildup of H2 O2 in roots when treated with SNP. We identified 222 DEGs. GO annotation of these DEGs revealed that all top 20 GO terms were related to stress responses. Moreover, three DEGs were annotated to GA-related processes (DDF1, DDF2, EXPA1), and seven DEGs were associated with root development (RAV1, RGF2, ERF71, ZAT6, MYB77, XT1, and DTX50). In summary, NO inhibits primary root growth partially by repressing GA3-oxidase catalysed GA3 synthesis in Arabidopsis. ROS, Ca2+ , DDF1, DDF2, EXPA1 and seven root development-related genes may be involved in crosstalk between NO and GAs.

Analysis of the 2OG‐Fe (II) oxygenase family reveals new insights associated with flowering regulation in Saccharum spontaneum

AbstractPlant flowering is a crucial phenomenon affecting crop yield and crossbreeding. Saccharum spontaneum is the closest wild relative sugarcane species widely used in sugarcane genetic improvement. However, the molecular interactions among the components of the flowering regulatory network of S. spontaneum are still unclear. In this study, we conducted a transcriptome sequencing approach to analyze the expressed genes on four developmental stages of panicle samples in S. spontaneum. The weighted gene co‐expression network analysis (WGCNA) results suggested that genes from the MEred (p = 3 × 10−4) module were significantly enriched in pathways of ABC transporters, photosynthesis, and circadian rhythm‐plant. Thus, 23 genes associated with flower development‐related genes were screened, including 7 AGL24, 1 FLC, 3 VIN3, 3 GA20ox, and 9 ELF3. In the gibberellic acid (GA) synthesis pathway, GA20ox, GA3ox, and GA2ox were the three enzymes that catalyzed later reactions of GA biosynthesis and belong to the 2‐oxoglutarate Fe (II) oxygenase (2OG) superfamily. Flavonoid synthesis was promoted by 2‐oxoglutarate Fe (II) oxygenase genes, a flowering hormone, which catalyzed and oxidized naringenin to dihydrokaempferol, an important precursor of florigen. Genome‐wide analysis revealed that 122 Ss2OG genes were identified in S. spontaneum, of which 99 genes were enriched in the panicle transcriptome. Furthermore, a quantitative reverse transcription polymerase chain reaction analysis showed that Ss2OG‐FeII_Oxy90, Ss2OG‐FeII_Oxy47, and Ss2OG‐FeII_Oxy89 could introduce the flower development, while Ss2OG‐FeII_Oxy34, Ss2OG‐FeII_Oxy37, and Ss2OG‐FeII_Oxy50 inhibited it. These findings provide new clues and resources for exploring the molecular mechanism of flowering regulation in S. spontaneum and promoting sugarcane breeding.

Gibberellic Acid Inhibits Dendrobium nobile-Piriformospora Symbiosis by Regulating the Expression of Cell Wall Metabolism Genes.

Orchid seeds lack endosperms and depend on mycorrhizal fungi for germination and nutrition acquisition under natural conditions. Piriformospora indica is a mycorrhizal fungus that promotes seed germination and seedling development in epiphytic orchids, such as Dendrobium nobile. To understand the impact of P. indica on D. nobile seed germination, we examined endogenous hormone levels by using liquid chromatography-mass spectrometry. We performed transcriptomic analysis of D. nobile protocorm at two developmental stages under asymbiotic germination (AG) and symbiotic germination (SG) conditions. The result showed that the level of endogenous IAA in the SG protocorm treatments was significantly higher than that in the AG protocorm treatments. Meanwhile, GA3 was only detected in the SG protocorm stages. IAA and GA synthesis and signaling genes were upregulated in the SG protocorm stages. Exogenous GA3 application inhibited fungal colonization inside the protocorm, and a GA biosynthesis inhibitor (PAC) promoted fungal colonization. Furthermore, we found that PAC prevented fungal hyphae collapse and degeneration in the protocorm, and differentially expressed genes related to cell wall metabolism were identified between the SG and AG protocorm stages. Exogenous GA3 upregulated SRC2 and LRX4 expression, leading to decreased fungal colonization. Meanwhile, GA inhibitors upregulated EXP6, EXB16, and EXP10-2 expression, leading to increased fungal colonization. Our findings suggest that GA regulates the expression of cell wall metabolism genes in D. nobile, thereby inhibiting the establishment of mycorrhizal symbiosis.

Large-scale RNAseq analysis provide a new insight into the critical genes and regulatory networks of tiller development mediated by gibberellin in sugarcane

Tillering plays a key role in sugarcane growth, development, and cane yield. Gibberellin (GA) and its biosynthesis inhibitor, paclobutrazol, have been used to manipulate the tiller production in sugarcane planting. However, the key genes and regulatory networks of sugarcane tiller development remain unclear. In this study, we applied GA3 and paclobutrazol to soak the sugarcane seeds for generating samples with varying tiller numbers. A total of 54 samples from multiple tissues of three tillering stages were employed for transcriptome sequencing using two full-length transcript isoform sequences datasets as reference. We observed significant downregulation of two genes within the GA metabolism pathway in response to the GA synthesis inhibitor. Additionally, we noted a substantial enrichment of genes associated with photosynthesis following treatment with GA3 or paclobutrazol. Using all the differentially expressed genes (DEGs) between each sample group, 41 gene modules were generated in the coexpression network. The associations between modules and traits were performed. The Gene Ontology (GO) enrichment, KEGG pathway enrichment, and hub genes analysis were implemented in the modules correlated with traits, especially, the modules correlated with GA3 content and tiller number were emphasized. Notably, the pathway of ubiquitin-mediated proteolysis were enriched in both the GA3 content positive correlated module and the tiller number negative correlated module, while an E3 ubiquitin ligase gene, RZFP34, was the top hub gene in these two modules, indicating the vital role of ubiquitin-mediated proteasomal degradation system in tillering regulation in sugarcane. Our study provides a comprehensive insight into regulatory networks involved in GA-mediated regulation of tiller development in sugarcane, which would lay the foundation of hormone regulation to promote sugarcane production.

Ectopic expression of Camellia oleifera Abel. gibberellin 20-oxidase gene increased plant height and promoted secondary cell walls deposition in Arabidopsis.

Ectopic expression of Camellia oleifera Abel. gibberellin 20-oxidase 1 caused a taller phenotype, promoted secondary cell wall deposition, leaf enlargement, and early flowering, and reduced chlorophyll and anthocyanin accumulation and seed enlargement phenotype in Arabidopsis. Plant height and secondary cell wall (SCW) deposition are important plant traits. Gibberellins (GAs) play important roles in regulating plant height and SCWs deposition. Gibberellin 20-oxidase (GA20ox) is an important enzyme involved in GA biosynthesis. In the present study, we identified a GA synthesis gene in Camellia oleifera. The total length of the CoGA20ox1 gene sequence was 1146bp, encoding 381 amino acids. Transgenic plants with CoGA20ox1 had a taller phenotype; a seed enlargement phenotype; promoted SCWs deposition, leaf enlargement, and early flowering; and reduced chlorophyll and anthocyanin accumulation. Genetic analysis showed that the mutant ga20ox1-3 Arabidopsis partially rescued the phenotype of CoGA20ox1 overexpression plants. The results showed that CoGA20ox1 participates in the growth and development of C. oleifera. The morphological changes in CoGA20ox1 overexpressed plants provide a theoretical basis for further exploration of GA biosynthesis and analysis of the molecular mechanism in C. oleifera.

GA20ox Family Genes Mediate Gibberellin and Auxin Crosstalk in Moso bamboo (Phyllostachys edulis).

Moso bamboo (Phyllostachys edulis) is one of the fastest growing plants. Gibberellin (GA) is a key phytohormone regulating growth, but there are few studies on the growth of Moso bamboo regulated by GA. The gibberellin 20 oxidase (GA20ox) gene family was targeted in this study. Chromosomal distribution and collinearity analysis identified 10 GA20ox genes evenly distributed on chromosomes, and the family genes were relatively conservative in evolution. The genetic relationship of GA20ox genes had been confirmed to be closest in different genera of plants in a phylogenetic and selective pressure analysis between Moso bamboo and rice. About 1/3 GA20ox genes experienced positive selective pressure with segmental duplication being the main driver of gene family expansion. Analysis of expression patterns revealed that only six PheGA20ox genes were expressed in different organs of shoot development and flowers, that there was redundancy in gene function. Underground organs were not the main site of GA synthesis in Moso bamboo, and floral organs are involved in the GA biosynthesis process. The auxin signaling factor PheARF47 was located upstream of PheGA20ox3 and PheGA20ox6 genes, where PheARF47 regulated PheGA20ox3 through cis-P box elements and cis-AuxRR elements, based on the result that promoter analysis combined with yeast one-hybrid and dual luciferase detection analysis identified. Overall, we identified the evolutionary pattern of PheGA20ox genes in Moso bamboo and the possible major synthesis sites of GA, screened for key genes in the crosstalk between auxin and GA, and laid the foundation for further exploration of the synergistic regulation of growth by GA and auxin in Moso bamboo.

Sl-lncRNA47980, a positive regulator affects tomato resistance to Phytophthora infestans

Emerging evidence suggests that long non-coding RNAs (lncRNAs) involve in defense respond against pathogen attack and show great potentials to improve plant resistance. Tomato late blight, a destructive plant disease, is caused by the oomycete pathogen Phytophthora infestans, which seriously affects the yield and quality of tomato. Our previous research has shown that Sl-lncRNA47980 is involved in response to P. infestans infection, but its molecular mechanism is unknown. Gain- and loss-of-function experiments revealed that Sl-lncRNA47980 as a positive regulator, played a crucial role in enhancing tomato resistance to P. infestans. The Sl-lncRNA47980-overexpressing transgenic plants exhibited an improved ability to scavenge reactive oxygen species (ROS), decreased contents of endogenous gibberellin (GA) and salicylic acid (SA), and increased contents of jasmonic acid (JA), while silencing of Sl-lncRNA47980 showed an opposite trend in the levels of these hormones. Furthermore, it was found that Sl-lncRNA47980 could upregulate the expression of SlGA2ox4 gene through activation of the promoter of SlGA2ox4 to affect GA content. The increased expression of the tomato GA signaling repressor SlDELLA could activate JA-related genes and inhibit SA-related genes to varying degrees respectively. In addition, exogenous application of GA3 and GA synthesis inhibitor uniconazole could increase disease susceptibility of Sl-lncRNA47980-overexpressing plants and the resistance of Sl-lncRNA47980-silenced plants, respectively, to P. infestans. From thus, it was speculated that Sl-lncRNA47980 conferred tomato resistance to P. infestans, which was related to the decrease in endogenous GA content. Our study provided information to link Sl-lncRNA47980 with changes in ROS accumulation and phytohormone levels in plant immunity, thus providing a new candidate gene for tomato breeding.

Overexpression of brassinosteroid synthesis gene DWARF promotes resistance to Botrytis cinerea by inhibiting gibberellin synthesis in Solanum lycopersicum L.

Brassinosteroids (BRs) are a group of steroid hormones that play essential roles in plant growth and development. However, the roles of BRs in plant defense to pathogens are mainly studied in Arabidopsis, and there are few studies reporting the effects of BRs on plant resistance to Botrytis cinerea, an important pathogen in horticulture. Here, we found that high levels of BRs increased B. cinerea resistance in tomato (Solanum lycopersicum). Enhancing the expression of DWARF (DWF), a rate-limiting gene in BRs synthesis, in tomato resulted in a decrease in lesion area in detached leaf assay, and attenuated the leaf damages in the intact plants assay, as compared to wild type. Application of 24-epibrassinolide (EBL) at a saturation level also induced the B. cinerea resistance, with the upregulation of protease inhibitor encoding genes. Silencing of BAK1, which encodes the coreceptor of BR receptor BRI1 and the critical regulator of innate immunity, could not suppress BR-induced B. cinerea resistance. Interestingly, the bioactive gibberellins (GAs) were strongly decreased, while the expression of GAI, the tomato homologue of DELLA which suppresses GA signaling, was increased in DWF-OE plants. Silencing of GAI strongly compromised BR-induced B. cinerea resistance. The results indicated that increasing the BRs levels by either overexpression of DWF or application of high dose of EBL enhanced tomato resistance to B. cinerea. BRs levels exceeding the optimum may inhibit GA synthesis and signaling, and thus enhance the defense response.

Sink Strength During Sugarcane Culm Growth: Size Matters

Sugarcane growth and its subsequent yield are linked to plant height. The increase in sugarcane height is controlled by elongation of the top 6 to 7 internodes. The elongation of the internodes can be significantly reduced by an application of the Trinexapac-ethyl (Moddus®) which is a known disruptor of GA synthesis. In this study, the growth and composition of the internodes were analysed following the treatment. We found that the strong inhibitory effect of Moddus® on internode size was due to a strongly suppressed rate of internode elongation, with no effect on the duration of the elongation period. The Moddus® inhibition of internode elongation was not due to a lack of an osmotic potential gradient but probably reflects a higher pressure potential of the tissue. A consequence of the reduced internode size was a significant reduction in carbon flow (sink strength) of the internode. It was not only the rate of internode growth that was altered by Moddus®, but also partitioning within the internode. Partitioning of carbon into components other than the soluble sugars and cell wall was significantly reduced by the Moddus® treatment. The high reducing sugar content in the Moddus® treatment suggests that sucrose mobilisation (hydrolysis by invertases and cleavage by sucrose synthase) might, like the duration of elongation, be controlled by thermal time. No accumulation of reducing sugars was evident in the control internodes probably due to the rapid mobilisation to other cellular processes. Sucrose accumulation in the internode reflected a cessation of sugar utilisation to support growth and maintenance.

Gibberellic Acid Alleviates Cadmium-Induced Seed Germination Inhibition through Modulation of Carbohydrate Metabolism and Antioxidant Capacity in Mung Bean Seedlings

Gibberellins (GA) are the decisive players in seed germination whose functionality could be adversely affected by the presence of cadmium (Cd); however, the underlying mechanisms are unclear. Eco-toxicological effects of Cd (0, 25, 50, 75, and 100 µM) on the early stages of ontogenesis in a mung bean variety (ML-2056) were investigated. Seed germination characteristics along with Cd-tolerance index were recorded at the seventh day of germination. Additionally, endogenous gibberellic acid (GA3) level, amylase activity, oxidative stress, and the antioxidant defense system were also investigated in Cd-stressed germinating seedlings. Results revealed that Cd reduced seed germination and interfered with GA synthesis in a concentration-dependent manner. Further, to validate the role of GA in Cd-tolerance, experiments were executed to explore the effect of seed priming with GA3 and its biosynthesis inhibitor paclobutrazol (PBZ) on ML-2056 under Cd stress. Application of GA3 improved the activities of amylase and carbohydrate-metabolizing enzymes, the antioxidant defense system, and sustained lower H2O2 and TBARS contents, whereas PBZ caused a significant reduction in growth and decreased endogenous GA3 content in Cd-stressed ML-2056, suggesting a crucial role of GA synthesis in reversing Cd-induced negative effects. Overall, GA synthesis played a crucial role in mitigating Cd toxicity in mung bean, which might be used as a criterion for developing Cd-stress-tolerant genotypes.

QTL analysis of important agronomic traits and metabolites in foxtail millet (Setaria italica) by RIL population and widely targeted metabolome.

As a bridge between genome and phenotype, metabolome is closely related to plant growth and development. However, the research on the combination of genome, metabolome and multiple agronomic traits in foxtail millet (Setaria italica) is insufficient. Here, based on the linkage analysis of 3,452 metabolites via with high-quality genetic linkage maps, we detected a total of 1,049 metabolic quantitative trait loci (mQTLs) distributed in 11 hotspots, and 28 metabolite-related candidate genes were mined from 14 mQTLs. In addition, 136 single-environment phenotypic QTL (pQTLs) related to 63 phenotypes were identified by linkage analysis, and there were 12 hotspots on these pQTLs. We futher dissected 39 candidate genes related to agronomic traits through metabolite-phenotype correlation and gene function analysis, including Sd1 semidwarf gene, which can affect plant height by regulating GA synthesis. Combined correlation network and QTL analysis, we found that flavonoid-lignin pathway maybe closely related to plant architecture and yield in foxtail millet. For example, the correlation coefficient between apigenin 7-rutinoside and stem diameter reached 0.98, and they were co-located at 41.33-44.15 Mb of chromosome 5, further gene function analysis revealed that 5 flavonoid pathway genes, as well as Sd1, were located in this interval . Therefore, the correlation and co-localization between flavonoid-lignins and plant architecture may be due to the close linkage of their regulatory genes in millet. Besides, we also found that a combination of genomic and metabolomic for BLUP analysis can better predict plant agronomic traits than genomic or metabolomic data, independently. In conclusion, the combined analysis of mQTL and pQTL in millet have linked genetic, metabolic and agronomic traits, and is of great significance for metabolite-related molecular assisted breeding.

Overexpression of gibberellin 2-oxidase 4 from tall fescue affected plant height, tillering and drought tolerance in rice

Gibberellin (GA) is an important phytohormone that regulates plant growth and development. GA-2-oxidases (GA2oxs) have been found to affect plant height, tillering and stress tolerance by inactivating endogenous bioactive GAs. The present study aimed to isolate GA2oxs genes from tall fescue (Festuca arundinacea), analyze their expression level under abiotic stresses (10% PEG6000 induced drought stress, 150 mM NaCl induced salt stress, heat stress at 38 °C, and cold stress at 4 °C) and search for valuable genes for improving stress tolerance. Among eight FaGA2ox genes, FaGA2ox4 was found to represent a highest expression level at 24 h of PEG-induced drought stress and was chosen for further analysis. Compared with wildtype plants, transgenic rice plants overexpressing FaGA2ox4 exhibited a dwarf and high-tillering phenotype and the dwarf phenotype was partially compensated by foliar application of 10 μM GA3. In addition, transgenic plants showed improved drought stress tolerance, as manifested by higher leaf relative water content and lower electrolyte leakage than wildtype. Further qRT-PCR analysis demonstrated that the enhanced drought stress tolerance may be associated with decreased expression levels of genes involved in chlorophyll degradation (OsSGRL) and GA synthesis (OsGA3ox1) as well as increased expression of ABA-synthesizing gene (OsNCED3) in transgenic plants overexpressing FaGA2ox4.