DELLA-GAF1 Complex Is a Main Component in Gibberellin Feedback Regulation of GA20 Oxidase 2

Reprogramming feedback strength in gibberellin biosynthesis highlights conditional regulation by the circadian clock and carbon dioxide

The phytohormone gibberellin (GA) is an important regulator of plant morphology and reproduction, and the biosynthesis and distribution of GA in planta is agriculturally relevant to past and current breeding efforts. Tools like biosensors, extensive molecular genetic resources in reference plants and mathematical models have greatly contributed to current understanding of GA homeostasis; however, these tools are difficult to tune or repurpose for engineering crop plants. Previously, we showed that a GA-regulated Hormone Activated CAS9-based Repressor (GAHACR) functions in planta. Here, we use GAHACRs to modulate the strength of feedback on endemic GA regulated genes, and to directly test the importance of transcriptional feedback in GA signaling. We first adapted existing mathematical models to predict the impact of targeting a GAHACR to different nodes in the GA biosynthesis pathway, and then implemented a perturbation predicted by the model to lower GA levels. Specifically, we individually targeted either the biosynthetic gene GA20 oxidase (GA20ox) or the GA receptor GID1, and characterized primary root length, flowering time and the transcriptome of these transgenic lines. Using this approach, we identified a strong connection between GA signaling status and the circadian clock, which can be largely attenuated by elevated carbon dioxide levels. Our results identify a node in the GA signaling pathway that can be engineered to modulate plant size and flowering time. Our results also raise concerns that rising atmospheric CO2 concentration are likely to reverse many of the gains of Green Revolution crops.

MEDIATOR15 destabilizes DELLA protein to promote gibberellin-mediated plant development

Mediator, a transcriptional coactivator, regulates plant growth and development by interacting with various transcriptional regulators. MEDIATOR15 (MED15) is a subunit in the Mediator complex potentially involved in developmental control. To uncover molecular functions of Arabidopsis MED15 in development, we searched for its interactors. MED15 was found to interact with DELLA proteins, which negatively regulate gibberellic acid (GA) signaling and positively regulate GA biosynthesis. Mutants and overexpressors of MED15 exhibited multiple GA-related growth phenotypes, which resembled the phenotypes of the DELLA overexpressor and mutant, respectively. Consistent with this observation, DELLA protein levels were inversely correlated with MED15 protein levels, suggesting that MED15 activates GA signaling through DELLA degradation. MED15 was required not only for DELLA-mediated induction of GA-biosynthesis gene expression but also for GA-mediated degradation of DELLA. Therefore, MED15 facilitates DELLA destruction not only by promoting GA biosynthesis but also by accelerating DELLA turnover. Furthermore, MED15-mediated GA signaling was required for timely developmental responses to dark and warm conditions. Our results provide insight into developmental control by Mediator via precise regulation of DELLA stability. These findings are potentially useful for the generation of new crop cultivars with ideal body architecture.

SUMOylation of rice DELLA SLR1 modulates transcriptional responses and improves yield under salt stress

MAIN CONCLUSION

SUMOylation of SLR1 at K2 protects productivity under salt stress, possibly by modulation of SLR1 interactome. DELLA proteins modulate GA signaling and are major regulators of plant plasticity to endure stress. DELLAs are mostly regulated at the post-translational level, and their activity relies on the interaction with upstream regulators and transcription factors (TFs). SUMOylation is a post-translational modification (PTM) capable of changing protein interaction and has been found to influence DELLA activity in Arabidopsis. We determined that SUMOylation of the single rice DELLA, SLENDER RICE1 (SLR1), occurs in a lysine residue different from the one identified in Arabidopsis REPRESSOR OF GA (RGA). Artificially increasing the SUMOylated SLR1 levels attenuated the penalty of salt stress on rice yield. Gene expression analysis revealed that the overexpression of SUMOylated SLR1 can regulate GA biosynthesis, which could partially explain the sustained productivity upon salt stress imposition. Furthermore, SLR1 SUMOylation blocked the interaction with the growth regulator YAB4, which may fine-tune GA20ox2 expression. We also identified novel SLR1 interactors: bZIP23, bHLH089, bHLH094, and OSH1. All those interactions were impaired in the presence of SUMOylated SLR1. Mechanistically, we propose that SUMOylation of SLR1 disrupts its interaction with several transcription factors implicated in GA-dependent growth and ABA-dependent salinity tolerance to modulate downstream gene expression. We found that SLR1 SUMOylation represents a novel mechanism modulating DELLA activity, which attenuates the impact of stress on plant performance.

Functional Characterization of the Gibberellin (GA) Receptor ScGID1 in Sugarcane

Sugarcane smut caused by Sporisorium scitamineum represents the most destructive disease in the sugarcane industry, causing host hormone disruption and producing a black whip-like sorus in the apex of the stalk. In this study, the gibberellin metabolic pathway was found to respond to S. scitamineum infection, and the contents of bioactive gibberellins were significantly reduced in the leaves of diseased plants. The gibberellin receptor gene ScGID1 was identified and significantly downregulated. ScGID1 localized in both the nucleus and cytoplasm and had the highest expression level in the leaves. Eight proteins that interact with ScGID1 were screened out using a yeast two-hybrid assay. Novel DELLA proteins named ScGAI1a and ScGA20ox2, key enzymes in GA biosynthesis, were both found to interact with ScGID1 in a gibberellin-independent manner. Transcription factor trapping with a yeast one-hybrid system identified 50 proteins that interacted with the promoter of ScGID1, among which ScS1FA and ScPLATZ inhibited ScGID1 transcription, while ScGDSL promoted transcription. Overexpression of ScGID1 in transgenic Nicotiana benthamiana plants could increase plant height and promote flowering. These results not only contribute to improving our understanding of the metabolic regulatory network of sugarcane gibberellin but also expand our knowledge of the interaction between sugarcane and pathogens.

Functional characterization of WsPR-1 reveals its interplay with cytokinin and gibberellin signaling pathways

Pathogenesis-related protein 1 (PR-1) is an antimicrobial protein involved in systemic acquired resistance (SAR) in plants, but its regulatory role and interactions with other pathways remain unclear. In this study, we functionally characterize WsPR-1 gene of Withania somnifera in Nicotiana tabacum to elucidate its role in plant defense, growth, and development. Interestingly, transgenic tobacco plants with increased levels of cytokinin (CK) and decreased gibberellins (GAs) exhibited stunted shoot growth, an underdeveloped root system, modified leaf morphology, reduced seed pod production, and delayed leaf senescence. Transcriptional analysis revealed that WsPR-1 overexpression downregulated the GA 20-oxidase (GA20ox) gene involved in GA biosynthesis while upregulating GA 2-oxidase (GA2ox), a GA catabolic enzyme. Moreover, transcript levels of FRUITFULL (FUL) and LEAFY (NFL2) flowering genes exhibited a decrease in WsPR-1 plants, which could explain the delayed flowering and reduced seed pod development in transgenic plants. Confocal microscopy confirmed increased lignin deposition in stem cross-sections of WsPR-1 transgenic plants, supported by gene expression analysis and lignin content quantification. Additionally, our findings also suggest the involvement of Knotted1-like homeobox (KNOX) gene in enhancing cytokinin levels. This study highlights PR-1's regulatory role in plant growth and development, with potential to boost crop yields and enhance resilience.

A LBD transcription factor from moso bamboo, PheLBD12, regulates plant height in transgenic rice

The regulation mechanism of bamboo height growth has always been one of the hotspots in developmental biology. In the preliminary work of this project, the function of LBD transcription factor regulating height growth was firstly studied. Here, a gene PheLBD12 regulating height growth was screened. PheLBD12-overexpressing transgenic rice had shorter internodes, less bioactive gibberellic acid (GA3), and were more sensitive to GA3 than wild-type (WT) plants, which implied that PheLBD12 involve in gibberellin (GA) pathway. The transcript levels of OsGA2ox3, that encoding GAs deactivated enzyme, was significantly enhanced in PheLBD12-overexpressing transgenic rice. The transcript levels of OsAP2-39, that directly regulating the expression of EUI1 to reduce GA levels, was also significantly enhanced in PheLBD12-overexpressing transgenic rice. Expectedly, yeast one-hybrid assays, Dual-luciferase reporter assay and EMSAs suggested that PheLBD12 directly interacted with the promoter of OsGA2ox3 and OsAP2-39. Together, our results reveal that PheLBD12 regulates plant height growth by modulating GA catabolism. Through the research of this topic, it enriches the research content of LBD transcription factors and it will theoretically enrich the research content of height growth regulation.

Crape myrtle LiGAoxs displaying activities of gibberellin oxidases respond to branching architecture

In the realm of ornamental horticulture, crape myrtle (Lagerstroemia indica) stands out for its aesthetic appeal, attributed largely to its vibrant flowers and distinctive branching architecture. This study embarked on a comprehensive exploration of the gibberellin oxidase (GAox) gene family in crape myrtle, illuminating its pivotal role in regulating GA levels, a key determinant of plant developmental processes. We identified and characterized 36 LiGAox genes, subdivided into GA2ox, GA3ox, GA20ox, and GAox-like subgroups, through genomic analyses. These genes' evolutionary trajectories were delineated, revealing significant gene expansions attributed to segmental duplication events. Functional analyses highlighted the divergent expression patterns of LiGAox genes across different crape myrtle varieties, associating them with variations in flower color and branching architecture. Enzymatic activity assays on selected LiGA2ox enzymes exhibited pronounced GA2 oxidase activity, suggesting a potential regulatory role in GA biosynthesis. Our findings offered a novel insight into the molecular underpinnings of GA-mediated growth and development in L. indica, providing a foundational framework for future genetic enhancements aimed at optimizing ornamental traits.

MeGT2.6 increases cellulose synthesis and active gibberellin content to promote cell enlargement in cassava

Cassava, a pivotal tropical crop, exhibits rapid growth and possesses a substantial biomass. Its stem is rich in cellulose and serves as a crucial carbohydrate storage organ. The height and strength of stems restrict the mechanised operation and propagation of cassava. In this study, the triple helix transcription factor MeGT2.6 was identified through yeast one-hybrid assay using MeCesA1pro as bait, which is critical for cellulose synthesis. Over-expression and loss-of-function lines were generated, and results revealed that MeGT2.6 could promote a significant increase in the plant height, stem diameter, cell size and thickness of SCW of cassava plant. Specifically, MeGT2.6 upregulated the transcription activity of MeGA20ox1 and downregulated the expression level of MeGA2ox1, thereby enhancing the content of active GA3, resulting in a large cell size, high plant height and long stem diameter in cassava. Moreover, MeGT2.6 upregulated the transcription activity of MeCesA1, which promoted the synthesis of cellulose and hemicellulose and produced a thick secondary cell wall. Finally, MeGT2.6 could help supply additional substrates for the synthesis of cellulose and hemicellulose by upregulating the invertase genes (MeNINV1/6). Thus, MeGT2.6 was found to be a multiple regulator; it was involved in GA metabolism and sucrose decomposition and the synthesis of cellulose and hemicellulose.

C-TERMINAL DOMAIN PHOSPHATASE-LIKE 3 contributes to GA-mediated growth and flowering by interaction with DELLA proteins

Gibberellic acid (GA) plays a central role in many plant developmental processes and is crucial for crop improvement. DELLA proteins, the core suppressors in the GA signaling pathway, are degraded by GA via the 26S proteasomal pathway to release the GA response. However, little is known about the phosphorylation-mediated regulation of DELLA proteins. In this study, we combined GA response assays with protein-protein interaction analysis to infer the connection between Arabidopsis thaliana DELLAs and the C-TERMINAL DOMAIN PHOSPHATASE-LIKE 3 (CPL3), a phosphatase involved in the dephosphorylation of RNA polymerase II. We show that CPL3 directly interacts with DELLA proteins and promotes DELLA protein stability by inhibiting its degradation by the 26S proteasome. Consequently, CPL3 negatively modulates multiple GA-mediated processes of plant development, including hypocotyl elongation, flowering time, and anthocyanin accumulation. Taken together, our findings demonstrate that CPL3 serves as a novel regulator that could improve DELLA stability and thereby participate in GA signaling transduction.

Characterization, expression pattern, and function analysis of gibberellin oxidases in Salix matsudana

Gibberellin oxidases (GAoxs) identified from many species play indispensable roles in GA biosynthesis and GA signal transduction. However, there has been limited research conducted on the GAox family of Salix matsudana, a tetraploid ornamental tree species. Here, 54 GAox genes were identified from S. matsudana and renamed as SmGA20ox1-22, SmGA2ox1-24, SmGA3ox1-6, and SmGAox-like1/2. Gene structure and conserved motif analysis showed that SmGA3ox members possess the 1 intron and other SmGAoxs contain 2-3 introns, and motif 1/2/7 universally present in all SmGAoxs. A total of 69 gene pairs were identified from SmGAox family members, and the Ka/Ks values indicated the SmGAoxs experience the purifying selection. The intra species collinearity analysis implied S. matsudana, S. purpurea, and Populus trichocarpa have the close genetic relationship. The GO analysis suggested SmGAoxs are dominantly involved in GA metabolic process, ion binding, and oxidoreductase activity. RNA-sequencing demonstrated that some SmGAoxs may play an essential role in salt and submergence stresses. In addition, the SmGA20ox13/21 displayed the dominant vitality of GA20 oxidase, but the SmGA20ox13/21 still possessed low activities of GA2 and GA3 oxidases. This study can contribute to reveal the regulatory mechanism of salt and submergence tolerance in willow.

OsNAC120 balances plant growth and drought tolerance by integrating GA and ABA signaling in rice

The crosstalk between gibberellin (GA) and abscisic acid (ABA) signaling is crucial for balancing plant growth and adaption to environmental stress. Nevertheless, the molecular mechanism of their mutual antagonism still remains to be fully clarified. In this study, we found that knockout of the rice NAC (NAM, ATAF1/2, CUC2) transcription factor gene OsNAC120 inhibits plant growth but enhances drought tolerance, whereas OsNAC120 overexpression produces the opposite results. Exogenous GA can rescue the semi-dwarf phenotype of osnac120 mutants, and further study showed that OsNAC120 promotes GA biosynthesis by transcriptionally activating the GA biosynthetic genes OsGA20ox1 and OsGA20ox3. The DELLA protein SLENDER RICE1 (SLR1) interacts with OsNAC120 and impedes its transactivation ability, and GA treatment can remove the inhibition of transactivation activity caused by SLR1. On the other hand, OsNAC120 negatively regulates rice drought tolerance by repressing ABA-induced stomatal closure. Mechanistic investigation revealed that OsNAC120 inhibits ABA biosynthesis via transcriptional repression of the ABA biosynthetic genes OsNCED3 and OsNCED4. Rice OSMOTIC STRESS/ABA-ACTIVATED PROTEIN KINASE 9 (OsSAPK9) physically interacts with OsNAC120 and mediates its phosphorylation, which results in OsNAC120 degradation. ABA treatment accelerates OsNAC120 degradation and reduces its transactivation activity. Together, our findings provide evidence that OsNAC120 plays critical roles in balancing GA-mediated growth and ABA-induced drought tolerance in rice. This research will help us to understand the mechanisms underlying the trade-off between plant growth and stress tolerance and to engineer stress-resistant, high-yielding crops.

The Roles of Mepiquate Chloride and Melatonin in the Morpho-Physiological Activity of Cotton under Abiotic Stress

Cotton growth and yield are severely affected by abiotic stress worldwide. Mepiquate chloride (MC) and melatonin (MT) enhance crop growth and yield by reducing the negative effects of abiotic stress on various crops. Numerous studies have shown the pivotal role of MC and MT in regulating agricultural growth and yield. Nevertheless, an in-depth review of the prominent performance of these two hormones in controlling plant morpho-physiological activity and yield in cotton under abiotic stress still needs to be documented. This review highlights the effects of MC and MT on cotton morpho-physiological and biochemical activities; their biosynthetic, signaling, and transduction pathways; and yield under abiotic stress. Furthermore, we also describe some genes whose expressions are affected by these hormones when cotton plants are exposed to abiotic stress. The present review demonstrates that MC and MT alleviate the negative effects of abiotic stress in cotton and increase yield by improving its morpho-physiological and biochemical activities, such as cell enlargement; net photosynthesis activity; cytokinin contents; and the expression of antioxidant enzymes such as catalase, peroxidase, and superoxide dismutase. MT delays the expression of NCED1 and NCED2 genes involved in leaf senescence by decreasing the expression of ABA-biosynthesis genes and increasing the expression of the GhYUC5, GhGA3ox2, and GhIPT2 genes involved in indole-3-acetic acid, gibberellin, and cytokinin biosynthesis. Likewise, MC promotes lateral root formation by activating GA20x genes involved in gibberellin catabolism. Overall, MC and MT improve cotton's physiological activity and antioxidant capacity and, as a result, improve the ability of the plant to resist abiotic stress. The main purpose of this review is to present an in-depth analysis of the performance of MC and MT under abiotic stress, which might help to better understand how these two hormones regulate cotton growth and productivity.

Preliminary Study on the Formation Mechanism of Malformed Sweet Cherry (Prunus avium L.) Fruits in Southern China Using Transcriptome and Metabolome Data

Gibberellin (GA) is an important plant hormone that is involved in various physiological processes during plant development. Sweet cherries planted in southern China have always encountered difficulty in bearing fruit. In recent years, gibberellin has successfully solved this problem, but there has also been an increase in malformed fruits. This study mainly explores the mechanism of malformed fruit formation in sweet cherries. By analyzing the synthesis pathway of gibberellin using metabolomics and transcriptomics, the relationship between gibberellin and the formation mechanism of deformed fruit was preliminarily determined. The results showed that the content of GA3 in malformed fruits was significantly higher than in normal fruits. The differentially expressed genes in the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway were mainly enriched in pathways such as "plant hormone signal transduction", "diterpenoid biosynthesis", and "carotenoid biosynthesis". Using Quantitative Real-Time Reverse Transcription PCR (qRT-PCR) analysis, the gibberellin hydrolase gene GA2ox and gibberellin synthase genes GA20ox and GA3ox were found to be significantly up-regulated. Therefore, we speculate that the formation of malformed fruits in sweet cherries may be related to the accumulation of GA3. This lays the foundation for further research on the mechanism of malformed sweet cherry fruits.

Gibberellin signaling regulates lignin biosynthesis to modulate rice seed shattering

The elimination of seed shattering was a key step in rice (Oryza sativa) domestication. In this paper, we show that increasing the gibberellic acid (GA) content or response in the abscission region enhanced seed shattering in rice. We demonstrate that SLENDER RICE1 (SLR1), the key repressor of GA signaling, could physically interact with the rice seed shattering-related transcription factors quantitative trait locus of seed shattering on chromosome 1 (qSH1), O. sativa HOMEOBOX 15 (OSH15), and SUPERNUMERARY BRACT (SNB). Importantly, these physical interactions interfered with the direct binding of these three regulators to the lignin biosynthesis gene 4-COUMARATE: COENZYME A LIGASE 3 (4CL3), thereby derepressing its expression. Derepression of 4CL3 led to increased lignin deposition in the abscission region, causing reduced rice seed shattering. Importantly, we also show that modulating GA content could alter the degree of seed shattering to increase harvest efficiency. Our results reveal that the "Green Revolution" phytohormone GA is important for regulating rice seed shattering, and we provide an applicable breeding strategy for high-efficiency rice harvesting.

Jasmonate inhibits plant growth and reduces gibberellin levels via microRNA5998 and transcription factor MYC2

Jasmonate (JA) and gibberellins (GAs) exert antagonistic effects on plant growth and development in response to environmental and endogenous stimuli. Although the crosstalk between JA and GA has been elucidated, the role of JA in GA biosynthesis remains unclear. Therefore, in this study, we investigated the mechanism underlying JA-mediated regulation of endogenous GA levels in Arabidopsis (Arabidopsis thaliana). Transient and electrophoretic mobility shift assays showed that transcription factor MYC2 regulates GA inactivation genes. Using transgenic plants, we further evaluated the contribution of MYC2 in regulating GA inactivation genes. JA treatment increased DELLA accumulation but did not inhibit DELLA protein degradation. Additionally, JA treatment decreased bioactive GA content, including GA4, significantly decreased the expression of GA biosynthesis genes, including ent-kaurene synthase (AtKS), GA 3β-hydroxylase (AtGA3ox1), and AtGA3ox2, and increased the expression of GA inactivation genes, including GA 2 oxidase (AtGA2ox4), AtGA2ox7, and AtGA2ox9. Conversely, JA treatment did not significantly affect gene expression in the myc2 myc3 myc4 triple mutant, demonstrating the MYC2-4-dependent effects of JA in GA biosynthesis. Additionally, JA post-transcriptionally regulated AtGA3ox1 expression. We identified microRNA miR5998 as an AtGA3ox1-associated miRNA; its overexpression inhibited plant growth by suppressing AtGA3ox1 expression. Overall, our findings indicate that JA treatment inhibits endogenous GA levels and plant growth by decreasing the expression of GA biosynthesis genes and increasing the expression of GA inactivation genes via miR5998 and MYC2 activities.

Identification of early flowering mutant gene in Phalaenopsis amabilis (L.) Blume for sgRNA construction in CRISPR/Cas9 genome editing system

Phalaenopsis amabilis (L.) Blume commonly called Moth Orchid (Orchidaceae) is a natural orchid species designated as the National Flower of Indonesia for its beautiful flower shape and long-lasting flowering period. Basically, P. amabilis has a long vegetative phase that cause late flowering, about 2 to 3 years for flowering, hence a method to shorten vegetative period is desired. The latest technological approach that can be used to accelerate flowering of P. amabilis is the CRISPR/Cas9 genome editing method to inactivate the GAI (Gibberellic Acid Insensitive) gene as a mutant gene that can accelerate the regulation of FLOWERING TIME (FT) genes flowering biosynthesis pathway. The approach that needs to be taken is to silence the GAI gene with a knockout system which begins with identifying and characterizing the GAI target gene in the P. amabilis which will be used as a single guide RNA. CRISPR/Cas9 mediated knockout efficiency is highly dependent on the properties of the sgRNA used. SgRNA consists of a target sequence, determining its specificity performance. We executed phylogenetic clustering for the PaGAI protein with closely related orchid species such as Dendrobium capra, Dendrobium cultivars and Cymbidium sinensis. SWISS-Model as tool webserver for protein structure homology modeling. Results show that P. amabilis has a specific domain with the occurrence of point mutations in the two conservative domains. Therefore, a single guide RNA reconstruction needs to be implemented.

Comparative transcriptome profiling reveals the multiple levels of crosstalk in phytohormone networks in Brassica napus

Plant hormones are the intrinsic factors that control plant development. The integration of different phytohormone pathways in a complex network of synergistic, antagonistic and additive interactions has been elucidated in model plants. However, the systemic level of transcriptional responses to hormone crosstalk in Brassica napus is largely unknown. Here, we present an in-depth temporal-resolution study of the transcriptomes of the seven hormones in B. napus seedlings. Differentially expressed gene analysis revealed few common target genes that co-regulated (up- and down-regulated) by seven hormones; instead, different hormones appear to regulate distinct members of protein families. We then constructed the regulatory networks between the seven hormones side by side, which allowed us to identify key genes and transcription factors that regulate the hormone crosstalk in B. napus. Using this dataset, we uncovered a novel crosstalk between gibberellin and cytokinin in which cytokinin homeostasis was mediated by RGA-related CKXs expression. Moreover, the modulation of gibberellin metabolism by the identified key transcription factors was confirmed in B. napus. Furthermore, all data were available online from http://yanglab.hzau.edu.cn/BnTIR/hormone. Our study reveals an integrated hormone crosstalk network in Brassica napus, which also provides a versatile resource for future hormone studies in plant species.

Identification of GA20ox2 as a target of ATHB2 and TCP13 during shade response

The shade avoidance syndrome (SAS) is a collective adaptive response of plants under shade highlighted by characteristic phenotypes such as hypocotyl elongation, which is largely mediated by concerted actions of auxin and GA. We identified ATHB2, a homeodomain-leucine zipper (HD-Zip) domain transcription factor known to be rapidly induced under shade condition, as a positive regulator of GA biosynthesis necessary for the SAS by transactivating the expression of GA20ox2, a key gene in the GA biosynthesis pathway. Based on promoter deletion analysis, EMSA and ChIP assay, ATHB2 appears to regulate the GA20ox2 expression as a direct binding target. We also found that the GA20ox2 expression is under negative control by TCP13, the effect of which can be suppressed by presence of ATHB2. Considering a rapid induction kinetics of ATHB2, this relationship between ATHB2 and TCP13 may allow ATHB2 to play a shade-specific activator for GA20ox by derepressing a pre-existing activity of TCP13.

Exogenously applied melatonin alleviates the damage in cucumber plants caused by Aphis goosypii through altering the insect behavior and inducing host plant resistance

BACKGROUND

Aphis gossypii Glover is the main pest found in most cucumber-producing areas. Melatonin (MT) has been widely studied in protecting plants from environmental stresses and pathogens. However, little knowledge is available on the impact of MT on insect resistance.

RESULTS

The fecundity of aphids on MT-treated cucumber leaves was inhibited. Interestingly, MT-treated plants were more attractive to aphids, which would prevent the large-scale transmission of viruses caused by the random movement of aphids. Meanwhile, MT caused varying degrees of change in enzyme activities related to methylesterified HG degradation, antioxidants, defense systems and membrane lipid peroxidation. Furthermore, transcriptomic analysis showed that MT induced 2360 differentially expressed genes (DEGs) compared with the control before aphid infection. These DEGs mainly were enriched in hormone signal transduction, MAPK signaling pathway, and plant-pathogen interaction, revealing that MT can help plants acquire inducible resistance and enhance plant immunity. Subsequently, 2397 DEGs were identified after aphid infection. Further analysis showed that MT-treated plants possessed stronger JA signal, reactive oxygen species stability, and the ability of flavonoid synthesis under aphid infection, while mediating plant growth and sucrose metabolism.

CONCLUSION

In summary, MT as an environmentally friendly substance mitigated aphid damage to cucumbers by affecting the aphids themselves and enhancing plant resistance. This will facilitate exploring sustainable MT-based strategies for cucumber aphid control. © 2022 Society of Chemical Industry.

Histone Deacetylase HDA15 Restrains PHYB-Dependent Seed Germination via Directly Repressing GA20ox1/2 Gene Expression

Seed germination is essential for the colonization of the land plants. Light is a major environmental factor affecting seed germination, which is predominantly regulated by photoreceptor phytochrome B (PHYB). PHYB is activated by red light (designated as PHYB-on) whereas it is inactivated by far-red light (referred as PHYB-off). We previously reported that Arabidopsis histone deacetylase HDA15 interacts with phytochrome-interacting factor1 (PIF1) to repress seed germination under PHYB-off conditions. Here, we show that HDA15 plays a negative role in regulating seed germination under PHYB-on conditions. Overexpression of HDA15 in Arabidopsis restrains PHYB-dependent seed germination, while gibberellin (GA) relieves the repressive role of HDA15 under PHYB-off conditions. We further show that HDA15 directly binds to GA20ox1 and GA20ox2, two key GA biosynthesis genes and represses their expression by removal of histone H3 and H4 acetylation. Moreover, the levels of HDA15 transcript and HDA15 protein are up-regulated in the phyB mutant. Collectively, our work proposes that HDA15 acts as a negative regulator of PHYB-dependent seed germination by directly repressing GA20ox1/2 gene expression.

The distribution of bioactive gibberellins along peach annual shoots is closely associated with PpGA20ox and PpGA2ox expression profiles

Background

The rapid growth of annual shoots is detrimental to peach production. While gibberellin (GA) promotes the rapid growth of peach shoots, there is limited information on the identity and expression profiles of GA-metabolism genes for this species.

Results

All six GA biosynthetic gene families were identified in the peach genome, and the expression profiles of these family members were determined in peach shoots. The upstream biosynthetic gene families have only one or two members (1 CPS, 2 KSs, and 1 KO), while the downstream gene families have multiple members (7 KAOs, 6 GA20oxs, and 5 GA3oxs). Between the two KS genes, PpKS1 showed a relatively high transcript level in shoots, while PpKS2 was undetectable. Among the seven KAO genes, PpKAO2 was highly expressed in shoots, while PpKAO1 and − 6 were weakly expressed. For the six GA20ox genes, both PpGA20ox1 and − 2 were expressed in shoots, but PpGA20ox1 levels were higher than PpGA20ox2. For the five GA3ox genes, only PpGA3ox1 was highly expressed in shoots. Among these biosynthesis genes, PpGA20ox1 and PpGA3ox1 showed a gradual decrease in transcript level along shoots from top to bottom, and a similar trend was observed in bioactive GA₁ and GA₄ distribution. Among the GA-deactivation genes, PpGA2ox6 was highly expressed in peach shoots. PpGA2ox1 and − 5 transcripts were relatively lower and showed a similar pattern to PpGA20ox1 and PpGA3ox1 in peach shoots. Overexpression of PpGA20ox1, − 2, or PpGA2ox6 in Arabidopsis or tobacco promoted or depressed the plant growth, respectively, while PpGA3ox1 did not affect plant height. Transient expression of PpGA20ox1 in peach leaves significantly increased bioactive GA₁ content.

Conclusions

Our results suggest that PpGA20ox and PpGA2ox expression are closely associated with the distribution of active GA₁ and GA₄ in peach annual shoots. Our research lays a foundation for future studies into ways to effectively repress the rapid growth of peach shoot.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08943-5.

Evolutionary and Integrative Analysis of Gibberellin-Dioxygenase Gene Family and Their Expression Profile in Three Rosaceae Genomes (F. vesca, P. mume, and P. avium) Under Phytohormone Stress

The gibberellin-dioxygenase (GAox) gene family plays a crucial role in regulating plant growth and development. GAoxs, which are encoded by many gene subfamilies, are extremely critical in regulating bioactive GA levels by catalyzing the subsequent stages in the biosynthesis process. Moreover, GAoxs are important enzymes in the GA synthesis pathway, and the GAox gene family has not yet been identified in Rosaceae species (Prunus avium L., F. vesca, and P. mume), especially in response to gibberellin and PCa (prohexadione calcium; reduce biologically active GAs). In the current investigation, 399 GAox members were identified in sweet cherry, Japanese apricot, and strawberry. Moreover, they were further classified into six (A-F) subgroups based on phylogeny. According to motif analysis and gene structure, the majority of the PavGAox genes have a remarkably well-maintained exon-intron and motif arrangement within the same subgroup, which may lead to functional divergence. In the systematic investigation, PavGAox genes have several duplication events, but segmental duplication occurs frequently. A calculative analysis of orthologous gene pairs in Prunus avium L., F. vesca, and P. mume revealed that GAox genes are subjected to purifying selection during the evolutionary process, resulting in functional divergence. The analysis of cis-regulatory elements in the upstream region of the 140 PavGAox members suggests a possible relationship between genes and specific functions of hormone response-related elements. Moreover, the PavGAox genes display a variety of tissue expression patterns in diverse tissues, with most of the PavGAox genes displaying tissue-specific expression patterns. Furthermore, most of the PavGAox genes express significant expression in buds under phytohormonal stresses. Phytohormones stress analysis demonstrated that some of PavGAox genes are responsible for maintaining the GA level in plant-like Pav co4017001.1 g010.1.br, Pav sc0000024.1 g340.1.br, and Pav sc0000024.1 g270.1.mk. The subcellular localization of PavGAox protein utilizing a tobacco transient transformation system into the tobacco epidermal cells predicted that GFP signals were mostly found in the cytoplasm. These findings will contribute to a better understanding of the GAox gene family's interaction with prohexadione calcium and GA, as well as provide a strong framework for future functional characterization of GAox genes in sweet cherry.

The VvWRKY37 Regulates Bud Break in Grape Vine Through ABA-Mediated Signaling Pathways

Dormancy is a common survival strategy in plants to temporarily suspend visible growth under unsuitable conditions. The elaborate mechanism underlying bud break in perennial woody plants is gradually illustrated. Here, we identified a grape vine WRKY transcription factor, VvWRKY37, which was highly expressed in dormant buds. It was particularly induced by the application of exogenous abscisic acid, and depressed on exposure to gibberellin and low temperature (4°C) stress at the transcript level. The yeast one-hybrid assay confirmed that VvWRKY37 had a transcriptional activity. Ectopic over-expression of VvWRKY37 significantly delayed bud break of transgenic poplar plants. As an ABA-inducible gene, VvWRKY37 also depressed the expression of ABA catabolic gene CYP707As and enhanced the accumulation of endogenous ABA in transgenic poplar plants. The molecular pieces of evidence showed that VvWRKY37 preferentially recognized and bound W-box 5'-G/CATTGACT/C/G-3' cis-element in vitro. Additionally, VvABI5 and VvABF2 acted as the upstream transcriptional activators of VvWRKY37 via protein-DNA interactions. Taken together, our findings provided valuable insights into a new regulatory mechanism of WRKY TF by which it modulates bud break through ABA-mediated signaling pathways.

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.

Roles of Abscisic Acid and Gibberellins in Stem/Root Tuber Development

Root and tuber crops are of great importance. They not only contribute to feeding the population but also provide raw material for medicine and small-scale industries. The yield of the root and tuber crops is subject to the development of stem/root tubers, which involves the initiation, expansion, and maturation of storage organs. The formation of the storage organ is a highly intricate process, regulated by multiple phytohormones. Gibberellins (GAs) and abscisic acid (ABA), as antagonists, are essential regulators during stem/root tuber development. This review summarizes the current knowledge of the roles of GA and ABA during stem/root tuber development in various tuber crops.

Interactions of Gibberellins with Phytohormones and Their Role in Stress Responses

Gibberellins are amongst the main plant growth regulators. Discovered over a century ago, the interest in gibberellins research is growing due to their current and potential applications in crop production and their role in the responses to environmental stresses. In the present review, the current knowledge on gibberellins’ homeostasis and modes of action is outlined. Besides this, the complex interrelations between gibberellins and other plant growth regulators are also described, providing an intricate network of interactions that ultimately drives towards precise and specific gene expression. Thus, genes and proteins identified as being involved in gibberellin responses in model and non-model species are highlighted. Furthermore, the molecular mechanisms governing the gibberellins’ relation to stress responses are also depicted. This review aims to provide a comprehensive picture of the state-of-the-art of the current perceptions of the interactions of gibberellins with other phytohormones, and their responses to plant stresses, thus allowing for the identification of the specific mechanisms involved. This knowledge will help us to improve our understanding of gibberellins’ biology, and might help increase the biotechnological toolbox needed to refine plant resilience, particularly under a climate change scenario.

LsRGL1 controls the bolting and flowering times of lettuce by modulating the gibberellin pathway

Bolting, which is a serious problem during lettuce (Lactuca sativa L.) production, is responsible for substantial annual yield and quality losses. Gibberellin plays a critical role in the regulation of lettuce bolting. Additionally, DELLA proteins negatively regulate the gibberellin signaling pathway. However, it is unclear if DELLA proteins are involved in the regulation of lettuce bolting. Therefore, in this study, we identified four DELLA-encoding genes in lettuce, including LsRGL1, which was highly expressed in the stem and negatively correlated with bolting. Knocking down this gene in lettuce promoted bolting, whereas its overexpression inhibited bolting and the biosynthesis of gibberellin and auxin. A transcriptome analysis revealed that genes involved in gibberellin and auxin biosynthesis and flowering were affected in the LsRGL1-overexpressing lines. The yeast two-hybrid and yeast one-hybrid assay results indicated that LsRGL1 can interact with LsGA3ox and the LsYUC4 promoter region. Considered together, the results of this study suggest LsRGL1 negatively regulates lettuce bolting. Furthermore, its function may depend on modifications to gibberellin and auxin levels mediated at the transcript and protein levels.

The HB40-JUB1 transcriptional regulatory network controls gibberellin homeostasis in Arabidopsis

The gibberellins (GAs) are phytohormones that play fundamental roles in almost every aspect of plant growth and development. Although GA biosynthetic and signaling pathways are well understood, the mechanisms that control GA homeostasis remain largely unclear in plants. Here, we demonstrate that the homeobox transcription factor (TF) HB40 of the HD-Zip family regulates GA content at two additive control levels in Arabidopsis thaliana. We show that HB40 expression is induced by GA and in turn reduces the levels of endogenous bioactive GAs by simultaneously reducing GA biosynthesis and increasing GA deactivation. Consistently, HB40 overexpression leads to typical GA-deficiency traits, such as small rosettes, reduced plant height, delayed flowering, and male sterility. By contrast, a loss-of-function hb40 mutation enhances GA-controlled growth. Genome-wide RNA sequencing combined with molecular-genetic analyses revealed that HB40 directly activates the transcription of JUNGBRUNNEN1 (JUB1), a key TF that represses growth by suppressing GA biosynthesis and signaling. HB40 also activates genes encoding GA 2-oxidases (GA2oxs), which are major GA-catabolic enzymes. The effect of HB40 on plant growth is ultimately mediated through the induction of nuclear growth-repressing DELLA proteins. Collectively, our results reveal the important role of the HB40-JUB1 regulatory network in controlling GA homeostasis during plant growth.

Finding a breather for Oryza sativa: Understanding hormone signalling pathways involved in rice plants to submergence stress

During the course of evolution, different ecotypes of rice (Oryza sativa L.) have evolved distinct strategies to cope with submergence stress. Such contrasting responses are mediated by plant hormones that are principle regulators of growth, development and responses to various biotic and abiotic stresses. These hormones act cooperatively and show extensive crosstalk which is mediated by key regulatory genes that serve as nodes of molecular communication. The presence or absence of such genes leads to significant changes in hormone signalling pathways and hence, governs the type of response that the plant will exhibit. As flooding is one of the leading causes of crop loss across all the major rice-producing countries, it is crucial to deeply understand the molecular nexus governing the response to submergence to produce flood resilient varieties. This review focuses on the hormonal signalling pathways that mediate two contrasting responses of the rice plant to submergence stress namely, rapid internode elongation to escape flood waters and quiescence response that enables the plant to survive under complete submergence. The significance of several key genes such as Sub1A-1, SLR1, SD1 and SK1/SK2, in defining the ultimate response to submergence has also been discussed.

Inhibition of gibberellin accumulation by water deficiency promotes fast and long-term 'drought avoidance' responses in tomato

Plants reduce transpiration to avoid dehydration during drought episodes by stomatal closure and inhibition of canopy growth. Previous studies have suggested that low gibberellin (GA) activity promotes these 'drought avoidance' responses. Using genome editing, molecular, physiological and hormone analyses, we examined if drought regulates GA metabolism in tomato (Solanum lycopersicum) guard cells and leaves, and studied how this affects water loss. Water deficiency inhibited the expression of the GA biosynthesis genes GA20 oxidase1 (GA20ox1) and GA20ox2 and induced the GA deactivating gene GA2ox7 in guard cells and leaf tissue, resulting in reduced levels of bioactive GAs. These effects were mediated by abscisic acid-dependent and abscisic acid-independent pathways, and by the transcription factor TINY1. The loss of GA2ox7 attenuated stomatal response to water deficiency and during soil dehydration, ga2ox7 plants closed their stomata later, and wilted faster than wild-type (WT) M82 cv. Mutations in GA20ox1 and GA20ox2, had no effect on stomatal closure, but reduced water loss due to the mutants' smaller canopy areas. The results suggested that drought-induced GA deactivation in guard cells, contributes to stomatal closure at the early stages of soil dehydration, whereas inhibition of GA synthesis in leaves suppresses canopy growth and restricts transpiration area.

Characterization of the molecular mechanism underlying the dwarfism of dsh mutant watermelon plants

Developing dwarf watermelon is a major objective among breeders. The dsh dwarf watermelon germplasm developed in our laboratory is genetically stable. We previously produced preliminary evidence that Cla010726, which encodes a gibberellin 20-oxidase-like protein, is the primary gene controlling dwarfism in watermelon. However, the underlying genetic mechanism was unknown. In this study, we characterized the spontaneous recessive mutant dsh, which is a gibberellin (GA)-deficient mutant. Many of the phenotypic traits of dsh plants are similar to those of known GA-deficient mutants. The dsh plants were sensitive to exogenous bioactive GAs, which increased seedling height. Moreover, a quantitative analysis of endogenous GA₃ proved that the bioactive GA₃ content was substantially lower than normal in dsh. Additionally, the T₅ClaGA20ox RNAi plants generally exhibited dwarfism, with short stems and internodes as well as small leaves and fruit. An examination of the transgenic plants carrying the ClaGA20ox1 promoter-GUS and mutant ClaGA20ox2 promoter-GUS constructs confirmed that two promoter sites are involved in the regulation of ClaGA20ox expression. Hence, mutations in the promoter of the GA20ox gene, which encodes a key enzyme involved in gibberellin biosynthesis, lead to the dwarfism of watermelon plants. The dsh mutant is a potentially useful germplasm resource for developing new watermelon varieties exhibiting dwarfism.

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.

DELLA degradation by gibberellin promotes flowering via GAF1-TPR-dependent repression of floral repressors in Arabidopsis

Flowering is the developmental transition from the vegetative to the reproductive phase. FLOWERING LOCUS T (FT), SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 (SOC1), and LEAFY (LFY) are floral integrators. These genes are repressed by several floral repressors including EARLY FLOWERING3 (ELF3), SHORT VEGETATIVE PHASE (SVP), TEMPRANILLO1 (TEM1), and TEM2. Although gibberellin (GA) promotes flowering by activating the floral integrator genes, the exact molecular mechanism remains unclear. DELLAs are negative regulators in GA signaling and act as coactivators of the transcription factor GAI ASSOCIATED FACTOR 1 (GAF1). GAs convert the GAF1 complex from a transcriptional activator to a repressor. Here, we show that GAF1 functions in the GA-dependent flowering pathway by regulating FT and SOC1 expression in Arabidopsis thaliana. We identified four flowering repressors, ELF3, SVP, TEM1, and TEM2, as GAF1-target genes. In response to GAs, GAF1 forms a transcriptional repressor complex and promotes the expression of FT and SOC1 through the repression of four flowering repressor genes, ELF3, SVP, TEM1, and TEM2.

Regulatory mechanism of GA3 on tuber growth by DELLA-dependent pathway in yam (Dioscorea opposita)

Endogenous and exogenous GA₃ responses to DoEXP and DoXTH depend on the DoGA20ox1, DoGA3ox1, DoGA2ox3, DoGA2ox4, DoGID1a, and DoDELLA1 to regulate yam tuber growth. Yam tuber undergoes significant alteration in morphogenesis and functions during growth, and gibberellins (GA) are considered potentially important regulators of tuber growth. However, it is little known about the regulation of GA metabolism and GA signaling components genes in tuber growth of yam. In this study, the cloning and expressions of GA₃ level, GA metabolism and signaling genes, and cell wall genes in tuber growth in response to GA₃ and GA biosynthesis inhibitor paclobutrazol (PP₃₃₃) treatments were studied. The contents of GA₃ accumulated at the tuber growth, with the highest levels in the early expansion stage. DoGA20ox1, DoGA3ox1, and four DoGA2ox genes were significantly abundant in the early expansion stage of tuber and gradually declined along with tuber growth. Three DoGID1 and three DoDELLA genes were showed different expression patterns in the early expansion stage of tuber and gradually declined along with tuber growth. Five DoEXP and three DoXTH genes expression levels were higher in the early expansion stage than in other stages. Exogenous GA₃ increased endogenous GA₃ levels, whereas the expression levels of DoGA20ox1, DoGA3ox1, DoGID1a, and DoDELLA1 were down-regulated in the early expansion stage of tuber by GA₃ treatment, DoGA2ox3 and DoGA2ox4 were up-regulated. PP₃₃₃ application exhibited opposite consequences. Thus, a mechanism of GA₃ regulating yam tuber growth by DELLA-dependent pathway is established.

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.

Pre-harvest sprouting in cereals: genetic and biochemical mechanisms

With the growth of the global population and the increasing frequency of natural disasters, crop yields must be steadily increased to enhance human adaptability to risks. Pre-harvest sprouting (PHS), a term mainly used to describe the phenomenon in which grains germinate on the mother plant directly before harvest, is a serious global problem for agricultural production. After domestication, the dormancy level of cultivated crops was generally lower than that of their wild ancestors. Although the shortened dormancy period likely improved the industrial performance of cereals such as wheat, barley, rice, and maize, the excessive germination rate has caused frequent PHS in areas with higher rainfall, resulting in great economic losses. Here, we systematically review the causes of PHS and its consequences, the major indicators and methods for PHS assessment, and emphasize the biological significance of PHS in crop production. Wheat quantitative trait loci functioning in the control of PHS are also comprehensively summarized in a meta-analysis. Finally, we use Arabidopsis as a model plant to develop more complete PHS regulatory networks for wheat. The integration of this information is conducive to the development of custom-made cultivated lines suitable for different demands and regions, and is of great significance for improving crop yields and economic benefits.

Overexpression of ovate family protein 22 confers multiple morphological changes and represses gibberellin and brassinosteroid signalings in transgenic rice

OVATE family proteins (OFPs) are plant-specific transcription factors that regulate plant growth and development. OFPs interact with 3-aa loop extension (TALE) homeodomain proteins and brassinosteroid (BR) signaling components to modulate gibberellic acid (GA) biosynthesis and BR responses. Bioactive GAs are essential in regulating plant organogenesis and organ growth by promoting cell differentiation and elongation. DELLA proteins act as the central repressors of GA-regulated processes and are targeted to be degraded by the 26S proteasome in the presence of GA. We discovered that the rice OFP22 negatively regulates GA and BR signal transduction. OsOFP22 expression was rapidly up-regulated by exogenous GA and BR application, detected predominantly in the calli and spikelets. Overexpression of OsOFP22 conferred multiple morphological phenotypes, including reduced plant height, dark green leaves, and shortened and widened leaves, floral organs and grains. The GA-induced elongation of the second leaf sheath in the seedlings, and α-amylase activity in the endosperms were attenuated in transgenic lines overexpressing OsOFP22, while GA-biosynthesis gene transcripts and bioactive GA₃ and GA₄ contents were increased in the transgenic plants. OsOFP22 promotes the protein accumulation of SLR1, the single DELLA in rice protein. Furthermore, Overexpression of OsOFP22 suppresses BR response and the expression of BR-related genes. OsOFP22 is thus involved in the repression of GA and BR signal transduction and integrates GA with BR to regulate plant growth and development.

SCARECROW-LIKE3 regulates the transcription of gibberellin-related genes by acting as a transcriptional co-repressor of GAI-ASSOCIATED FACTOR1

SCL3 inhibits transcriptional activity of IDD-DELLA complex by acting as a co-repressor and repression activity is enhanced in the presence of GAF1 in a TOPLESS-independent manner. GRAS [GIBBERELLIN-INSENSITIVE (GAI), REPRESSOR OF ga1-3 (RGA) and SCARECROW (SCR)] proteins are a family of plant-specific transcriptional regulators that play diverse roles in development and signaling. GRAS family DELLA proteins act as growth repressors by inhibiting gibberellin (GA) signaling in response to developmental and environmental cues. DELLAs also act as co-activators of transcription factor GAI-ASSOCIATED FACTOR1 (GAF1)/INDETERMINATE DOMAIN2 (IDD2), the GAF1-DELLA complex activating transcription of GAF1 target genes. GAF1 also interacts with TOPLESS (TPL), a transcriptional co-repressor, in the absence of DELLA, the GAF1-TPL complex repressing transcription of the target genes. SCARECROW-LIKE3 (SCL3), another member of the GRAS family, is thought to inhibit transcriptional activity of the IDD-DELLA complex through competitive interaction with IDD. Here, we also revealed that SCL3 inhibits transcriptional activation by the GAF1-DELLA complex via repression activity rather than via competitive inhibition of the GAF1-DELLA interaction. Moreover, the repression activity of SCL3 was enhanced by GAF1 in a TPL-independent manner. While the GRAS domain of DELLA has transcriptional activation activity, that of SCL3 has repression activity. SCL3 also inhibited transcriptional activity of GAF1-RGA fusion proteins. Results from the co-immunoprecipitation assays and the yeast three-hybrid assay suggested the possibility that SCL3 forms a ternary complex with GAF1 and DELLA. These findings provide important information on DELLA-regulated GA signaling and new insight into the transcriptional repression mechanism.

PHOSPHORYLETHANOLAMINE CYTIDYLYLTRANSFERASE 1 modulates flowering in a florigen-independent manner by regulating SVP

PHOSPHORYLETHANOLAMINE CYTIDYLYLTRANSFERASE 1 (PECT1) regulates phosphatidylethanolamine biosynthesis and controls the phosphatidylethanolamine:phosphatidylcholine ratio in Arabidopsis thaliana Previous studies have suggested that PECT1 regulates flowering time by modulating the interaction between phosphatidylcholine and FLOWERING LOCUS T (FT), a florigen, in the shoot apical meristem (SAM). Here, we show that knockdown of PECT1 by artificial microRNA in the SAM (pFD::amiR-PECT1) accelerated flowering under inductive and even non-inductive conditions, in which FT transcription is almost absent, and in ft-10 twin sister of ft-1 double mutants under both conditions. Transcriptome analyses suggested that PECT1 affects flowering by regulating SHORT VEGETATIVE PHASE (SVP) and GIBBERELLIN 20 OXIDASE 2 (GA20ox2). SVP misexpression in the SAM suppressed the early flowering of pFD::amiR-PECT1 plants. pFD::amiR-PECT1 plants showed increased gibberellin (GA) levels in the SAM, concomitant with the reduction of REPRESSOR OF GA1-3 levels. Consistent with this, GA treatment had little effect on flowering time of pFD::amiR-PECT1 plants and the GA antagonist paclobutrazol strongly affected flowering in these plants. Together, these results suggest that PECT1 also regulates flowering time through a florigen-independent pathway, modulating SVP expression and thus regulating GA production.

Isoprenoid-Derived Metabolites and Sugars in the Regulation of Flowering Time: Does Day Length Matter?

In plants, a diverse set of pathways regulate the transition to flowering, leading to remarkable developmental flexibility. Although the importance of photoperiod in the regulation of flowering time is well known, increasing evidence suggests the existence of crosstalk among the flowering pathways regulated by photoperiod and metabolic pathways. For example, isoprenoid-derived phytohormones (abscisic acid, gibberellins, brassinosteroids, and cytokinins) play important roles in regulating flowering time. Moreover, emerging evidence reveals that other metabolites, such as chlorophylls and carotenoids, as well as sugar metabolism and sugar accumulation, also affect flowering time. In this review, we summarize recent findings on the roles of isoprenoid-derived metabolites and sugars in the regulation of flowering time and how day length affects these factors.

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.

A gibberellin methyltransferase modulates the timing of floral transition at the Arabidopsis shoot meristem

The transition from vegetative to reproductive growth is a key event in the plant life cycle. Plants therefore use a variety of environmental and endogenous signals to determine the optimal time for flowering to ensure reproductive success. These signals are integrated at the shoot apical meristem (SAM), which subsequently undergoes a shift in identity and begins producing flowers rather than leaves, while still maintaining pluripotency and meristematic function. Gibberellic acid (GA), an important hormone associated with cell growth and differentiation, has been shown to promote flowering in many plant species including Arabidopsis thaliana, but the details of how spatial and temporal regulation of GAs in the SAM contribute to floral transition are poorly understood. In this study, we show that the gene GIBBERELLIC ACID METHYLTRANSFERASE 2 (GAMT2), which encodes a GA-inactivating enzyme, is significantly upregulated at the SAM during floral transition and contributes to the regulation of flowering time. Loss of GAMT2 function leads to early flowering, whereas transgenic misexpression of GAMT2 in specific regions around the SAM delays flowering. We also found that GAMT2 expression is independent of the key floral regulator LEAFY but is strongly increased by the application of exogenous GA. Our results indicate that GAMT2 is a repressor of flowering that may act as a buffer of GA levels at the SAM to help prevent premature flowering.

Alternative splicing and duplication of PI-like genes in maize

Alternative splicing and duplication provide the possibility of functional divergence of MADS-box genes. Compared with its Arabidopsis counterpart PI gene, Zmm16 in maize recruits a new role in carpel abortion and floral asymmetry, whereas the other two duplicated genes, Zmm18/29, have not yet been attributed to any function in flower development as a typical B class gene does. Here, alternatively spliced transcripts of three PI^L genes were analyzed, among which we described the candidate functional isoforms and analyzed the potential effects of alternative splicing (AS) on protein-protein interactions as well, then their phylogenetic relationships with orthologs in typical grasses were further analyzed. Furthermore, we compared the cis-acting elements specific for three maize PI^L genes, especially the elements related to methyl jasmonate (MeJA) and gibberellic acid (GA), both hormones involved in the sex-determination process in maize. Together with the results from the co-expression networks during reproductive organ development, we speculated that, due to duplication and alternative splicing, Zmm18/29 may play a role in GA- and MeJA-related developmental process. These results provide novel clues for experimental validation of the evolutional meaning of maize PI^L genes.

CRISPR/Cas9 Directed Mutagenesis of OsGA20ox2 in High Yielding Basmati Rice (Oryza sativa L.) Line and Comparative Proteome Profiling of Unveiled Changes Triggered by Mutations

In rice, semi-dwarfism is among the most required characteristics, as it facilitates better yields and offers lodging resistance. Here, semi-dwarf rice lines lacking any residual transgene-DNA and off-target effects were generated through CRISPR/Cas9-guided mutagenesis of the OsGA20ox2 gene in a high yielding Basmati rice line, and the isobaric tags for relative and absolute quantification (iTRAQ) strategy was utilized to elucidate the proteomic changes in mutants. The results indicated the reduced gibberellins (GA₁ and GA₄) levels, plant height (28.72%), and flag leaf length, while all the other traits remained unchanged. The OsGA20ox2 expression was highly suppressed, and the mutants exhibited decreased cell length, width, and restored their plant height by exogenous GA₃ treatment. Comparative proteomics of the wild-type and homozygous mutant line (GXU43_9) showed an altered level of 588 proteins, 273 upregulated and 315 downregulated, respectively. The identified differentially expressed proteins (DEPs) were mainly enriched in the carbon metabolism and fixation, glycolysis/gluconeogenesis, photosynthesis, and oxidative phosphorylation pathways. The proteins (Q6AWY7, Q6AWY2, Q9FRG8, Q6EPP9, Q6AWX8) associated with growth-regulating factors (GRF2, GRF7, GRF9, GRF10, and GRF11) and GA (Q8RZ73, Q9AS97, Q69VG1, Q8LNJ6, Q0JH50, and Q5MQ85) were downregulated, while the abscisic stress-ripening protein 5 (ASR5) and abscisic acid receptor (PYL5) were upregulated in mutant lines. We integrated CRISPR/Cas9 with proteomic screening as the most reliable strategy for rapid assessment of the CRISPR experiments outcomes.

Herbaceous peony (Paeonia lactiflora Pall.) PlDELLA gene negatively regulates dormancy release and plant growth

DELLA protein plays a significant role in plant growth and development. In this study, PlDELLA with the open reading frame of 1866 bp in length was isolated from Paeonia lactiflora. Overexpression of PlDELLA in Arabidopsis thaliana showed that seed germination was significantly repressed as it took 144∼192 h for the OEs to reach 100 % germination and it required only 60 h for the WT. The OEs were also inhibited in bolting time and in plant vegetative growth. When PlDELLA was silenced in peony by virus-induced gene silencing method, peony budbreak occurred earlier by 8∼10 d and the vegetative growth was significantly accelerated compared with the control group. These results collectively indicated that PlDELLA negatively regulated dormancy release and plant growth. During chilling process to release peony endodormancy, PlDELLA expression down-regulated, and the content of both endogenous active GAs and ABA decreased, indicating decreasing of PlDELLA expression under chilling was not caused by the known gibberellin signal transduction pathway. Besides, PlDELLA had no interaction with the four screened PlWRKYs, PlWRKY13, PlWRKY18, PlWRKY40 or PlWRKY50. These findings not only enrich the knowledge of DELLA protein family, but also provide insights into understanding the function of PlDELLA protein in endodormancy release in peony.

Identification and genetic analysis of qCL1.2, a novel allele of the "green revolution" gene SD1 from wild rice (Oryza rufipogon) that enhances plant height

BACKGROUND

The exploitation of novel alleles from wild rice that were lost during rice cultivation could be very important for rice breeding and evolutionary studies. Plant height (PH) was a target of artificial selection during rice domestication and is still a target of modern breeding. The "green revolution" gene semi-dwarf 1 (SD1) were well documented and used in the past decades, allele from wild rice could provide new insights into the functions and evolution of this gene.

RESULTS

We identified a PH-related quantitative trait locus, qCL1.2,from wild riceusing a set of chromosome segment substitution lines. qCL1.2encodesa novel allele of SD1 gene. The wild allele of SD1 is a dominant locus that can significantly promote rice internode length by regulating the expression levels of genes involved in gibberellin biosynthesis and signal transduction. Nucleotide diversity and haplotype network analyses of the SD1 gene were performed using 2822 rice landraces. Two previously reported functional nucleotide polymorphisms clearly differentiated japonica and indica rice; however, they were not associated with PH selection. Other new functional nucleotide polymorphisms in the coding, but not promoter, regions were involved in PH selection during rice domestication. Our study increasesunderstanding of the rice SD1 gene and provides additional evidence of this gene's selection during rice domestication.

CONCLUSIONS

Our findings provide evidence thatSD1 gene from wild rice enhances plant height and new functional nucleotide polymorphisms of this gene were artificially selected during cultivated rice differentiation.

GROWTH-REGULATING FACTORS Interact with DELLAs and Regulate Growth in Cold Stress

DELLA proteins are repressors of the gibberellin (GA) hormone signaling pathway that act mainly by regulating transcription factor activities in plants. GAs induce DELLA repressor protein degradation and thereby control a number of critical developmental processes as well as responses to stresses such as cold. The strong effect of cold temperatures on many physiological processes has rendered it difficult to assess, based on phenotypic criteria, the role of GA and DELLAs in plant growth during cold stress. Here, we uncover substantial differences in the GA transcriptomes between plants grown at ambient temperature (21°C) and plants exposed to cold stress (4°C) in Arabidopsis (Arabidopsis thaliana). We further identify over 250, to the largest extent previously unknown, DELLA-transcription factor interactions using the yeast two-hybrid system. By integrating both data sets, we reveal that most members of the nine-member GRF (GROWTH REGULATORY FACTOR) transcription factor family are DELLA interactors and, at the same time, that several GRF genes are targets of DELLA-modulated transcription after exposure to cold stress. We find that plants with altered GRF dosage are differentially sensitive to the manipulation of GA and hence DELLA levels, also after cold stress, and identify a subset of cold stress-responsive genes that qualify as targets of this DELLA-GRF regulatory module.

Silencing of transcription factor encoding gene StTCP23 by small RNAs derived from the virulence modulating region of potato spindle tuber viroid is associated with symptom development in potato

Viroids are small, non-protein-coding RNAs which can induce disease symptoms in a variety of plant species. Potato (Solanum tuberosum L.) is the natural host of Potato spindle tuber viroid (PSTVd) where infection results in stunting, distortion of leaves and tubers and yield loss. Replication of PSTVd is accompanied by the accumulation of viroid-derived small RNAs (sRNAs) proposed to play a central role in disease symptom development. Here we report that PSTVd sRNAs direct RNA silencing in potato against StTCP23, a member of the TCP (teosinte branched1/Cycloidea/Proliferating cell factor) transcription factor family genes that play an important role in plant growth and development as well as hormonal regulation, especially in responses to gibberellic acid (GA). The StTCP23 transcript has 21-nucleotide sequence complementarity in its 3ʹ untranslated region with the virulence-modulating region (VMR) of PSTVd strain RG1, and was downregulated in PSTVd-infected potato plants. Analysis using 3ʹ RNA ligase-mediated rapid amplification of cDNA ends (3ʹ RLM RACE) confirmed cleavage of StTCP23 transcript at the expected sites within the complementarity with VMR-derived sRNAs. Expression of these VMR sRNA sequences as artificial miRNAs (amiRNAs) in transgenic potato plants resulted in phenotypes reminiscent of PSTVd-RG1-infected plants. Furthermore, the severity of the phenotypes displayed was correlated with the level of amiRNA accumulation and the degree of amiRNA-directed down-regulation of StTCP23. In addition, virus-induced gene silencing (VIGS) of StTCP23 in potato also resulted in PSTVd-like phenotypes. Consistent with the function of TCP family genes, amiRNA lines in which StTCP23 expression was silenced showed a decrease in GA levels as well as alterations to the expression of GA biosynthesis and signaling genes previously implicated in tuber development. Application of GA to the amiRNA plants minimized the PSTVd-like phenotypes. Taken together, our results indicate that sRNAs derived from the VMR of PSTVd-RG1 direct silencing of StTCP23 expression, thereby disrupting the signaling pathways regulating GA metabolism and leading to plant stunting and formation of small and spindle-shaped tubers.

Potato spindle tuber viroid (PSTVd) is a small RNA pathogen that causes severe pandemic diseases in potato. How this non-protein-coding RNA induces disease symptom development in potato is unknown, thereby hindering the development of effective control measures. Here we report the first evidence that PSTVd disease is caused by the silencing of StTCP23, a potato transcription factor encoding gene, by PSTVd-derived small-interfering RNA (siRNAs). Specifically, we demonstrate that 3ʹ untranslated region (UTR) region of StTCP23 mRNA contains a 21-nt sequence that is complementary to the virulence-modulating region (VMR) of PSTVd. Furthermore, we show that StTCP23 expression is repressed in PSTVd-infected potato, and this repression is accompanied by StTCP23 transcript cleavage within the identified region of complementary. In planta expression of VMR sequences as 21-nt artificial microRNAs (amiRNAs) or infection of potato plants with a virus-induced gene silencing vector containing a portion the StTCP23 coding sequence, results in reduced StTCP23 transcript abundance and the expression of PSTVd-like disease symptoms. Consistent with the predicted functional role of StTCP23 in regulating the gibberellic acid (GA) biosynthesis and signaling pathways, GA levels were reduced both in PSTVd-infected and amiRNA-expressing plants. Our results provide compelling evidence that StTCP23 positively regulates potato sprouting and tuber development via a GA-related mechanism, and that the disease symptoms that develop upon PSTVd infection result from silencing of StTCP23 by VMR-derived siRNAs.

Genome-Wide Identification and Expression Analysis of GA2ox, GA3ox, and GA20ox Are Related to Gibberellin Oxidase Genes in Grape (Vitis Vinifera L.)

Gibberellin (GAs) plays the important role in the regulation of grape developmental and growth processes. The bioinformatics analysis confirmed the differential expression of GA2, GA3, and GA20 gibberellin oxidase genes (VvGA2oxs, VvGA3oxs, and VvGA20oxs) in the grape genome, and laid a theoretical basis for exploring its role in grape. Based on the Arabidopsis GA2oxs, GA3oxs, and GA20oxs genes already reported, the VvGA2oxs, VvGA3oxs, and VvGA20oxs genes in the grape genome were identified using the BLAST software in the grape genome database. Bioinformatics analysis was performed using software such as DNAMAN v.5.0, Clustalx, MapGene2Chrom, MEME, GSDS v.2.0, ExPASy, DNAsp v.5.0, and MEGA v.7.0. Chip expression profiles were generated using grape Affymetrix GeneChip 16K and Grape eFP Browser gene chip data in PLEXdb. The expression of VvGA2oxs, VvGA3oxs, and VvGA20oxs gene families in stress was examined by qRT-PCR (Quantitative real-time-PCR). There are 24 GAoxs genes identified with the grape genome that can be classified into seven subgroups based on a phylogenetic tree, gene structures, and conserved Motifs in our research. The gene family has higher codon preference, while selectivity is negative selection of codon bias and selective stress was analyzed. The expression profiles indicated that the most of VvGAox genes were highly expressed under different time lengths of ABA (Abscisic Acid) treatment, NaCl, PEG and 5 °C. Tissue expression analysis showed that the expression levels of VvGA2oxs and VvGA20oxs in different tissues at different developmental stages of grapes were relatively higher than that of VvGA3oxs. Last but not least, qRT-PCR (Real-time fluorescent quantitative PCR) was used to determine the relative expression of the GAoxs gene family under the treatment of GA3 (gibberellin 3) and uniconazole, which can find that some VvGA2oxs was upregulated under GA3 treatment. Simultaneously, some VvGA3oxs and VvGA20oxs were upregulated under uniconazole treatment. In a nutshell, the GA2ox gene mainly functions to inactivate biologically active GAs, while GA20ox mainly degrades C20 gibberellins, and GA3ox is mainly composed of biologically active GAs. The comprehensive analysis of the three classes of VvGAoxs would provide a basis for understanding the evolution and function of the VvGAox gene family in a grape plant.