GA Response Research Articles

Gibberellins Act Downstream of Arabis PERPETUAL FLOWERING1 to Accelerate Floral Induction during Vernalization.

Regulation of flowering by endogenous and environmental signals ensures that reproduction occurs under optimal conditions to maximize reproductive success. Involvement of the growth regulator gibberellin (GA) in the control of flowering by environmental cues varies among species. Arabis alpina Pajares, a model perennial member of the Brassicaceae, only undergoes floral induction during vernalization, allowing definition of the role of GA specifically in this process. The transcription factor PERPETUAL FLOWERING1 (PEP1) represses flowering until its mRNA levels are reduced during vernalization. Genome-wide analyses of PEP1 targets identified genes involved in GA metabolism and signaling, and many of the binding sites in these genes were specific to the A. alpina lineage. Here, we show that the pep1 mutant exhibits an elongated-stem phenotype, similar to that caused by treatment with exogenous GA, consistent with PEP1 repressing GA responses. Moreover, in comparison with the wild type, the pep1 mutant contains higher GA4 levels and is more sensitive to GA prior to vernalization. Upon exposure to cold temperatures, GA levels fall to low levels in the pep1 mutant and in wild-type plants, but GA still promotes floral induction and the transcription of floral meristem identity genes during vernalization. Reducing GA levels strongly impairs flowering and inflorescence development in response to short vernalization treatments, but longer treatments overcome the requirement for GA. Thus, GA accelerates the floral transition during vernalization in A. alpina, the down-regulation of PEP1 likely increases GA sensitivity, and GA responses contribute to determining the length of vernalization required for flowering and reproduction.

Multiple Gibberellin Receptors Contribute to Phenotypic Stability under Changing Environments.

The pleiotropic and complex gibberellin (GA) response relies on targeted proteolysis of DELLA proteins mediated by a GA-activated GIBBERELLIN-INSENSITIVE DWARF1 (GID1) receptor. The tomato (Solanum lycopersicum) genome encodes for a single DELLA protein, PROCERA (PRO), and three receptors, SlGID1a (GID1a), GID1b1, and GID1b2, that may guide specific GA responses. In this work, clustered regularly interspaced short palindromic repeats (CRISPR) /CRISPR associated protein 9-derived gid1 mutants were generated and their effect on GA responses was studied. The gid1 triple mutant was extremely dwarf and fully insensitive to GA. Under optimal growth conditions, the three receptors function redundantly and the single gid1 mutants exhibited very mild phenotypic changes. Among the three receptors, GID1a had the strongest effects on germination and growth. Yeast two-hybrid assays suggested that GID1a has the highest affinity to PRO. Analysis of lines with a single active receptor demonstrated a unique role for GID1a in protracted response to GA that was saturated only at high doses. When the gid1 mutants were grown in the field under ambient changing environments, they showed phenotypic instability, the high redundancy was lost, and gid1a exhibited dwarfism that was strongly exacerbated by the loss of another GID1b receptor gene. These results suggest that multiple GA receptors contribute to phenotypic stability under environmental extremes.

Strigolactones regulate shoot elongation by mediating gibberellin metabolism and signaling in rice (Oryza sativa L.)

Strigolactones (SLs) are plant hormones that regulate diverse physiological processes including shoot elongation. However, little is known about the regulatory mechanism of SLs in rice shoot elongation. Our results demonstrate that defects in SL biosynthesis or signaling led to dwarfism, and the dwarf statures of SL-deficient mutant (d17) and SL-insensitive mutant (d14) were restored to wild-type (WT) by gibberellin (GA) treatment, indicating that their dwarfism was associated with decreased GA content or weakened GA sensitivity. Our results indicate that the bioactive GA1 contents in d17 and d14 were lower than those in WT, due to the downregulated transcription of GA biosynthesis genes and upregulated transcription of GA inactivation genes. Moreover, d17 and d14 exhibited weakened GA-responsive sensitivity compared with WT. Although the transcription levels of cell division- and cell elongation-related genes were upregulated by GA3 treatment, the increase in transcription of d17 and d14 was lower than that in WT. These results suggest that SL is required for rice shoot elongation by mediating GA metabolism and signaling. Therefore, a deficiency in SL biosynthesis or signaling leads to decreased GA content and weakened GA response, which in turn reduces shoot length by downregulating transcription levels of cell division- and cell elongation-related genes.

Defoliation and gibberellin synergistically induce tree peony flowering with non-structural carbohydrates as intermedia

Although the natural florescence of the tree peony is short, it can be lengthened by forcing culture. In this study, both defoliation or gibberellic acid (GA3) treatment individually induced tree peony (Paeonia suffruticosa ‘Luo Yang Hong’) flowering under forcing culture, and their combination (D + G) accelerated flowering with a GA3-overdose-like phenomenon, indicating that synergism between defoliation and GA3 treatment may occur. Both defoliation and GA3 treatment induced a GA response, including (i) increased GA3 production, (ii) increased PsCPS and PsGA3ox expression, and (iii) decreased PsGA2ox, PsGID1c, and PsGID2 expression; both treatments also positively influenced non-structural carbohydrate (NSC) accumulation. According to the expression of five PsSWEETs, PsSWEET2 and PsSWEET17 may redundantly exercise the crosstalk of defoliation and GA3 treatment by NSC distribution, whereas PsSWEET12 may act by GA modulation; no synergism resulting from the D + G treatment was detected. Tissue-specific analysis indicated that, in sepals, PsSWEET2 and PsSWET7 are both induced by defoliation and GA3 treatment, whereas PsSWEET2 expression showed synergism with the D + G treatment. In summary, defoliation and GA3 treatment synergistically induce tree peony flowering under forcing culture, and NSCs are suggested as key intermedia. Moreover, sepals may play key roles in their synergism, although more direct evidence is still needed.

Plant Stature Related receptor-like Kinanse2 (PSRK2) acts as a factor that determines stem elongation toward gibberellins response in rice.

Gibberellins (GAs) are a family of plant hormones that are important to multiple aspects of plant growth and development, especially stem elongation. A PSRK2 was obtained through screening and identifying RLK dominant negative mutants. Phenotype of the loss-of-function mutants, psrk2-DN and psrk2-RNAi, showed that PSRK2 could influence the length of the uppermost and fourth internodes, indicating that PSRK2 might regulate cell division in the intercalary meristems and/or cell elongation in the internodes. Moreover, the expression pattern showed that PSRK2 was strongly expressed in the joined-nodes after the start-up of reproductive growth, but undetectable in leaves. PSRK2 expression was also found to be induced by GA3, and PSRK2 was involved in GA signaling in cereal aleurone cells, and PSRK2 influence the relative length of the second leaf sheaths in seedling stage. These results indicate PSRK2 is a component of GA signaling pathway that controls stem elongation by negatively regulating GA responses. Abbreviations: Os: Oryza sativa; At: Arabidopsis thaliana; RNAi: RNA interfere; DN: Dominate Negative; SMART: Simple Modular Architecture Research Tool; Uni : Uniconazol; PSRK2: Plant Stature Related receptor-like Kinase 2; RLK: Receptor-like Kinase; GA: Gibberellin; IAA: indole-3-acetic acid; BL: Brassinosteroid.

Tomato floral induction and flower development are orchestrated by the interplay between gibberellin and two unrelated microRNA‐controlled modules

Age-regulated microRNA156 (miR156) and targets similarly control the competence to flower in diverse species. By contrast, the diterpene hormone gibberellin (GA) and the microRNA319-regulated TEOSINTE BRANCHED/CYCLOIDEA/PCF (TCP) transcription factors promote flowering in the facultative long-day Arabidopsis thaliana, but suppress it in the day-neutral tomato (Solanum lycopersicum). We combined genetic and molecular studies and described a new interplay between GA and two unrelated miRNA-associated pathways that modulates tomato transition to flowering. Tomato PROCERA/DELLA activity is required to promote flowering along with the miR156-targeted SQUAMOSA PROMOTER BINDING-LIKE (SPL/SBP) transcription factors by activating SINGLE FLOWER TRUSS (SFT) in the leaves and the MADS-Boxgene APETALA1(AP1)/MC at the shoot apex. Conversely, miR319-targeted LANCEOLATE represses floral transition by increasing GA concentrations and inactivating SFT in the leaves and AP1/MC at the shoot apex. Importantly, the combination of high GA concentrations/responses with the loss of SPL/SPB function impaired canonical meristem maturation and flower initiation in tomato. Our results reveal a cooperative regulation of tomato floral induction and flower development, integrating age cues (miR156 module) with GA responses and miR319-controlled pathways. Importantly, this study contributes to elucidate the mechanisms underlying the effects of GA in controlling flowering time in a day-neutral species.

Ectopic Expression of Two FOREVER YOUNG FLOWER Orthologues from Cattleya Orchid Suppresses Ethylene Signaling and DELLA Results in Delayed Flower Senescence/Abscission and Reduced Flower Organ Elongation in Arabidopsis

Two orthologues of Arabidopsis FOREVER YOUNG FLOWER (FYF), CaFYF1 and CaFYF2, were identified from Cattleya intermedia. To investigate the function of these two genes, we performed ectopic expression of CaFYF1/2 in Arabidopsis. Delayed flower senescence and abscission were observed in 35S::CaFYF1/2 transgenic Arabidopsis plants. Furthermore, once CaFYF1/2 was fused with the strong repressor domain SRDX, severe delayed flower senescence and abscission were observed in 35S::CaFYF1/2+SRDX transgenic Arabidopsis plants. In contrast, when 35S::CaFYF1/2 was converted to a potent activator by fusion with the VP16-AD motif, flower senescence and abscission were promoted in these 35S::CaFYF1/2+VP16 transgenic dominant-negative mutant Arabidopsis plants. These results indicated that similar to Arabidopsis FYF, CaFYF1/2 also act as repressors in controlling floral organ senescence and abscission in transgenic Arabidopsis plants. The delayed senescence and abscission of the flower organs in 35S::CaFYF1/2 and 35S::CaFYF1/2+SRDX transgenic Arabidopsis plants were unaffected by ethylene treatment. Genes of the ethylene signaling and abscission-associated pathways, such as EDF1/2/3/4, BOP1/2, and IDA, were repressed in 35S::CaFYF1/2 and 35S::CaFYF1/2+SRDX transgenic Arabidopsis plants. Furthermore, 35S::CaFYF1/2 and 35S::CaFYF1/2+SRDX transgenic Arabidopsis plants showed additional morphological defects, such as short sepals and petals, which were correlated with the upregulation of the DELLA genes RGA, GAI, RGL1, and RGL2. These results suggested a possible role for Cattleya orchid CaFYF1/2 in controlling floral senescence/abscission by suppressing ethylene signaling and abscission-associated genes as well as controlling flower organ elongation through negative regulation of GA response by activating the expression of the DELLA genes during flower development.

Positive and negative regulation of seed germination by the Arabidopsis GA hormone receptors, GID1a, b, and c.

Epistasis analysis of gid1 single and double mutants revealed that GID1c is a key positive regulator of seed germination, whereas the GID1b receptor can negatively regulate germination in dormant seeds and in the dark. The GID1 GA receptors were expected to positively regulate germination because the plant hormone gibberellin (GA) is required for seed germination in Arabidopsis thaliana. The three GA hormone receptors, GID1a, GID1b, and GID1c, positively regulate GA responses via GA/GID1‐stimulated destruction of DELLA (Asp‐Glu‐Leu‐Leu‐Ala) repressors of GA responses. The fact that the gid1abc triple mutant but not gid1 double mutants fail to germinate indicates that all three GA receptors can positively regulate non‐dormant seed germination in the light. It was known that the gid1abc triple mutant fails to lose dormancy through the dormancy breaking treatments of cold stratification (moist chilling of seeds) and dry after‐ripening (a period of dry storage). Previous work suggested that there may be some specialization of GID1 gene function during germination because GID1b mRNA expression was more highly induced by after‐ripening, whereas GID1a and GID1c mRNA levels were more highly induced by cold stratification. In light‐germinated dormant seeds, the gid1b mutation can partly rescue the germination efficiency of gid1a but not of gid1c seeds. Thus, GID1b can function as an upstream negative regulator GID1c, a positive regulator of dormant seed germination. Further experiments showed that GID1b can negatively regulate dark germination. Wild‐type Arabidopsis seeds do not germinate well in the dark. The gid1b and gid1ab double mutants germinated much more efficiently than wild type, gid1c, or gid1ac mutants in the dark. The observation that the gid1ab double mutant also shows increased dark germination suggests that GID1b, and to some extent GID1a, can act as upstream negative regulators of GID1c. Since the gid1abc triple mutant failed to germinate in the dark, it appears that GID1c is a key downstream positive regulator of dark germination. This genetic analysis indicates that the three GID1 receptors have partially specialized functions in GA signaling.

MOTHER-OF-FT-AND-TFL1 represses seed germination under far-red light by modulating phytohormone responses in Arabidopsis thaliana.

Seed germination in many plant species is triggered by sunlight, which is rich in the red (R) wavelength and repressed by under-the-canopy light rich in far red (FR). R:FR ratios are sensed by phytochromes to regulate levels of gibberellins (GAs) and abscisic acid (ABA), which induce and inhibit germination respectively. In this study we have discovered that, under FR light conditions, germination is repressed by MOTHER-OF-FT-AND-TFL1 (MFT) through the regulation of the ABA and GA signaling pathways. We also show that MFT gene expression is tightly regulated by light quality. Previous work has shown that under FR light conditions the transcription factor PHYOCHROME-INTERACTING-FACTOR1 (PIF1) accumulates and promotes expression of SOMNUS (SOM) that, in turn, leads to increased ABA and decreased GA levels. PIF1 also promotes expression of genes encoding ABA-INSENSITIVE5 (ABI5) and DELLA growth-repressor proteins, which act in the ABA and GA signaling pathways, respectively. Here we show that MFT gene expression is promoted by FR light through the PIF1/SOM/ABI5/DELLA pathway and is repressed by R light via the transcription factor SPATULA (SPT). Consistent with this, we also show that SPT gene expression is repressed under FR light in a PIF1-dependent manner. Furthermore, transcriptomic analyses presented in this study indicate that MFT exerts its function by promoting expression of known ABA-induced genes and repressing cell wall expansion-related genes.

Gibberellin Induces an Increase in Cytosolic Ca2+ via a DELLA-Independent Signaling Pathway.

DELLA proteins play a central role in gibberellin (GA) signaling. GA triggers DELLA degradation via the ubiquitin-proteasome pathway, thereby promoting plant growth. An increase in cytosolic Ca2+ ([Ca2+]cyt) was observed previously after several hours of GA application. Recent studies also suggest the existence of a DELLA-independent GA response. However, the effect of DELLA on the GA-induced increase in [Ca2+]cyt remains unknown. This study reexamined the effects of GAs on [Ca2+]cyt using the Ca2+ sensor protein aequorin in Arabidopsis (Arabidopsis thaliana). [Ca2+]cyt increased within a few minutes of GA treatment, even in transgenic plants expressing a mutated degradation-resistant version of REPRESSOR OF ga1-3 and in della pentuple mutant plants. In addition, it was also revealed that Ca2+ is not involved in DELLA degradation. These results suggest that the GA-induced increase in [Ca2+]cyt occurs via a DELLA-independent pathway, providing important information on the GA signaling network.

Tyrosine phosphorylation of the GARU E3 ubiquitin ligase promotes gibberellin signalling by preventing GID1 degradation

Gibberellin (GA) is a major hormone for plant growth and development. GA response is derived from the degradation of DELLA repressor proteins after GA-dependent complex formation of the GID1 GA receptor with DELLA. Genistein is a known tyrosine (Tyr) kinase inhibitor and inhibits DELLA degradation. However, the biological role of Tyr phosphorylation on the GA response remains unclear. Here, we demonstrate that GARU (GA receptor RING E3 ubiquitin ligase) mediates ubiquitin-dependent degradation of GID1, and that the TAGK2 plant Tyr-kinase is a target of genistein and inhibits GARU–GID1A interactions by phosphorylation of GARU at Tyr321. Genistein induces degradation of GID1 and accumulation of DELLA. Conversely, Arabidopsis garu mutant and TAGK2-overexpressing plants accelerate GID1 stabilization and DELLA degradation. Under salt stress, GARU suppresses seed germination. We propose that GA response is negatively regulated by GARU-dependent GID1 ubiquitination and positively by Tyr phosphorylation of GARU by TAGK2, and genistein inhibits GA signaling by TAGK2 inhibition.

Influence of TaGW2-6A on seed development in wheat by negatively regulating gibberellin synthesis

Gibberellins (GA) are involved in seed development and E3 ubiquitin-ligases actively participate in GA perception and signal transduction. TaGW2-6A encodes a RING E3 ubiquitin-ligase that negatively regulates grain size. Therefore, Chinese Spring (CS) and its TaGW2-6A allelic variants (NIL31) were investigated to elucidate the relative contribution of GA to the regulation of seed development in wheat. The expression levels of GA biosynthesis and response genes were higher in NIL31 than CS, especially those of GA 3-oxidase and GASA4. The expression of TaGW2-6A exhibited the opposite pattern compared with those of the GA biosynthesis and response genes in CS and NIL31. The results showed that the GA content of NIL31 was significantly higher than that of CS. Thus, TaGW2-6A had a negative relationship on GA synthesis and response genes. Moreover, after GA treatment, CS and NIL31 exhibited the opposite phenotypes and GA contents. These results demonstrate that allelic variation in TaGW2-6A increases the seed size via the GA hormone pathway. Transcriptional analysis and cytological analysis showed that TaGW2-6A allelic variants regulated GA synthesis via GA 3-oxidases, thereby leading to the higher expression of GASA4 to control endosperm cell elongation and division during grain filling. Finally, germination experiments were performed to elucidate the relationships between TaGW2-6A and GA synthesis and response genes in wheat with full fertility. These results provide new insights into the effects of the ubiquitination system mediated by TaGW2-6A on the GA hormone signaling pathway, thereby improving our understanding of the role of TaGW2-6A in seed development in wheat.

Transcriptome Analysis Reveals Differential Gene Expression and a Possible Role of Gibberellins in a Shade-Tolerant Mutant of Perennial Ryegrass.

The molecular basis behind shade tolerance in plants is not fully understood. Previously, we have shown that a connection may exist between shade tolerance and dwarfism, however, the mechanism connecting these phenotypes is not well understood. In order to clarify this connection, we analyzed the transcriptome of a previously identified shade-tolerant mutant of perennial ryegrass (Lolium perenne L.) called shadow-1. shadow-1 mutant plants are dwarf, and are significantly tolerant to shade in a number of environments compared to wild-type controls. In this study, we treated shadow-1 and wild-type plants with 95% shade for 2 weeks and compared the transcriptomes of these shade-treated individuals with both genotypes exposed to full light. We identified 2,200 differentially expressed genes (DEGs) (1,096 up-regulated and 1,104 down-regulated) in shadow-1 mutants, compared to wild type, following exposure to shade stress. Of these DEGs, 329 were unique to shadow-1 plants kept under shade and were not found in any other comparisons that we made. We found 2,245 DEGs (1,153 up-regulated and 1,092 down-regulated) in shadow-1 plants, compared to wild-type, under light, with 485 DEGs unique to shadow-1 plants under light. We examined the expression of gibberellin (GA) biosynthesis genes and found that they were down-regulated in shadow-1 plants compared to wild type, notably gibberellin 20 oxidase (GA20ox), which was down-regulated to 3.3% (96.7% reduction) of the wild-type expression level under shade conditions. One GA response gene, lipid transfer protein 3 (LTP3), was also down-regulated to 41.5% in shadow-1 plants under shade conditions when compared to the expression level in the wild type. These data provide valuable insight into a role that GA plays in dwarfism and shade tolerance, as exemplified by shadow-1 plants, and could serve as a guide for plant breeders interested in developing new cultivars with either of these traits.

Rice Root-knot Nematode Down Regulates GA-Gene to Establish Infection

Experiments were conducted to observe the role of gibberellin (GA) in the response of rice to infection by rice root-knot nematode, Meloidogyne graminicola. Gibberellin might have a negative effect on defence in Nipponbare against M. graminicola. On the other hand, an inhibitory effect to M. graminicola in Taichung 65 (wild type) was found when GA was applied exogenously. Galling was significantly and reproducibly lower in mutants, whether it was GA insensitive or GA deficient, than in Taichung 65. There were even significantly lower galls in these GA deficient mutants after GA treatment than in non-treated mutant plants. The expression of GA signaling gene Osgid1-7 was significantly higher only in whole root at 2 dpi (days post inoculation) but not in leaves or root tips. Even this gene was not differentially expressed in root and leaf tissues at later stage (6 dpi days post inoculation) of infection. The nematode inhibited biosynthesis of OsGA20ox in leaves at 2 dpi and, in both of leaves and roots at 6 dpi. The GA response gene AK073385 was also less expressed in root tip at 6 dpi (days post inoculation). These might help M. graminicola to continue their infection in Taichung 65.

Contrasting migratory responses of two closely related seabirds to long-term climate change

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 559:231-242 (2016) - DOI: https://doi.org/10.3354/meps11875 Contrasting migratory responses of two closely related seabirds to long-term climate change W. James Grecian1,*, Graeme A. Taylor2, Graeme Loh3, Rona A. R. McGill4, Colin M. Miskelly5, Richard A. Phillips6, David R. Thompson7, Robert W. Furness1 1Institute of Biodiversity, Animal Health & Comparative Medicine, College of Medical, Veterinary & Life Sciences, University of Glasgow, Glasgow G12 8QQ, UK 2Department of Conservation, PO Box 10420, Wellington 6143, New Zealand 3Department of Conservation, PO Box 5244, Dunedin 9058, New Zealand 4NERC Life Sciences Mass Spectrometry Facility, Scottish Universities Environmental Research Centre, Rankine Avenue, East Kilbride G75 0QF, UK 5Museum of New Zealand Te Papa Tongarewa, PO Box 467, Wellington 6140, New Zealand 6British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, Cambridge CB3 0ET, UK 7National Institute of Water and Atmospheric Research Ltd, Kilbirnie, Wellington 6021, New Zealand *Corresponding author: james.grecian@glasgow.ac.uk ABSTRACT: Many marine predators migrate between breeding and non-breeding areas to target resources that are seasonal but spatio-temporally predictable, and so are vulnerable to climate-induced changes in prey phenology and abundance. In the Southern Ocean, small petrels are major consumers, but perturbations in the ecosystem through ocean warming are altering food-web structure and have been linked to poleward shifts in the distribution of their cold-water zooplankton prey. In this study, we focused on 2 small congeneric petrels: the broad-billed prion Pachyptila vittata and the Antarctic prion P. desolata. Both are planktivorous, but the broad-billed prion specialises in feeding on large copepods. We investigated historical trends in non-breeding distribution by analysing feather stable isotope ratios from a time-series dating back to 1926, and examined contemporary non-breeding distributions of broad-billed prions tracked using miniaturised geolocation-immersion loggers. After controlling temporally for the Suess effect, we found that the δ13C signatures of Antarctic prions, but not broad-billed prions, declined during the study period. This suggests a southward shift in Antarctic prion non-breeding distribution over the last century. Both species exhibited significant declines in δ15N during the same period, indicative of long-term decreases in marine productivity in their moulting areas, or changes in the trophic structure of prey communities. Tracked broad-billed prions migrated ca. 1000 km to an area east of the breeding colony where the Louisville seamount chain bisects the subtropical front. Topographically driven upwellings are stable and predictable features and may be crucial in aggregating plankton. Targeting seamounts could therefore mitigate the impact of climate-induced prey shifts by providing refugia for the broad-billed prion. KEY WORDS: Biologging · Conservation · Migration · Moult · Movement · Non-breeding behaviour · Seamounts · Stable isotopes · Upwelling zones Full text in pdf format PreviousNextCite this article as: Grecian WJ, Taylor GA, Loh G, McGill RAR and others (2016) Contrasting migratory responses of two closely related seabirds to long-term climate change. Mar Ecol Prog Ser 559:231-242. https://doi.org/10.3354/meps11875 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 559. Online publication date: November 09, 2016 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2016 Inter-Research.

Gibberellins Regulate Ovule Integument Development by Interfering with the Transcription Factor ATS.

Gibberellins (GAs) are plant hormones that regulate most plant life cycle aspects, including flowering and fruit development. Here, we demonstrate the implication of GAs in ovule development. DELLA proteins, negative GA response regulators, act as positive factors for ovule integument development in a mechanism that involves transcription factor ABERRANT TESTA SHAPE (ATS). The seeds of the della global mutant, a complete loss-of-function of DELLA, and the ats-1 mutant are remarkably similar, with a round shape, a disorganized testa, and viviparism. These defects are the result of an alteration in integuments that fail to fully develop and are shorter than in wild-type plants. ats-1 also shows some GA-related phenotypes, for example, higher germination rates and early flowering. In fact, ats-1 has elevated GA levels due to the activation of GA biosynthesis genes, which indicates that ATS inhibits GA biosynthesis. Moreover, DELLAs and ATS proteins interact, which suggests the formation of a transcriptional complex that regulates the expression of genes involved in integument growth. Therefore, the repression of GA biosynthesis by ATS would result in the stabilization of DELLAs to ensure correct ATS-DELLA complex formation. The requirement of both activities to coordinate proper ovule development strongly argues that the ATS-DELLA complex acts as a key molecular factor. This work provides the first evidence for a role of GAs in ovule and seed development.

AtSWEET13 and AtSWEET14 regulate gibberellin-mediated physiological processes.

Transmembrane transport of plant hormones is required for plant growth and development. Despite reports of a number of proteins that can transport the plant hormone gibberellin (GA), the mechanistic basis for GA transport and the identities of the transporters involved remain incomplete. Here, we provide evidence that Arabidopsis SWEET proteins, AtSWEET13 and AtSWEET14, which are members of a family that had previously been linked to sugar transport, are able to mediate cellular GA uptake when expressed in yeast and oocytes. A double sweet13 sweet14 mutant has a defect in anther dehiscence and this phenotype can be reversed by exogenous GA treatment. In addition, sweet13 sweet14 exhibits altered long distant transport of exogenously applied GA and altered responses to GA during germination and seedling stages. These results suggest that AtSWEET13 and AtSWEET14 may be involved in modulating GA response in Arabidopsis.

Hormone and antioxidant responses of Lilium Oriental hybrids ‘Sorbonne’ bulblets to humic acid treatments in vitro

ABSTRACTThe lily cultivar introduction is a very long process and bulblet development a limiting element in the entire cycle. The aim of the present study was to acquire a highly synchronized model system to gain insight into the bulbing process. Subsequently, this system was implemented to quantify the efficacy of humic acid applications to evaluate the hypothesized positive effect on bulblet growth. Based on weight, bulblet production was promoted with low humic acid concentration treatment (0.2 mg/L, LHA), showing 0.47 g weight and 11.68 mm diameter, while inhibitory effects were observed with increased doses. LHA significantly decreased the gibberellic acid content, and a pronounced phytohormone balance (promotive/inhibitive) was observed, which might be beneficial for the translocation of assimilates from the shoot to sink organs (bulblets). Intriguingly, LHA increased superoxide dismutase, peroxidase, ascorbate peroxidase, catalase, and glutathione reductase activities compared with the control during the early development stages, implicating a possible role for elimination of reactive oxygen species, thereby favouring cell expansion. In conclusion, we initially reported the effects of HA on the development of bulbous plants, showing that a relatively low dose markedly increased the bulblets size via positive GA and antioxidant responses. However, the mechanism of action needs further evaluation.

The rice YABBY4 gene regulates plant growth and development through modulating the gibberellin pathway.

YABBY genes encode seed plant-specific transcription factors that play pivotal roles in diverse aspects of leaf, shoot, and flower development. Members of the YABBY gene family are primarily expressed in lateral organs in a polar manner and function to specify abaxial cell fate in dicotyledons, but this polar expression is not conserved in monocotyledons. The function of YABBY genes is therefore not well understood in monocotyledons. Here we show that overexpression of the rice (Oryza sativa L.) YABBY4 gene (OsYABBY4) leads to a semi-dwarf phenotype, abnormal development in the uppermost internode, an increased number of floral organs, and insensitivity to gibberellin (GA) treatment. We report on an important role for OsYABBY4 in negative control of the expression of a GA biosynthetic gene by binding to the promoter region of the gibberellin 20-oxidase 2 gene (GA20ox2), which is a direct target of SLR1 (the sole DELLA protein negatively controlling GA responses in rice). OsYABBY4 also suppresses the expression level of SLR1 and interacts with SLR1 protein. The interaction inhibits GA-dependent degradation of SLR1 and therefore leads to GA insensitivity. These data together suggest that OsYABBY4 serves as a DNA-binding intermediate protein for SLR1 and is associated with the GA signaling pathway regulating gene expression during plant growth and development.

Molecular Characterization of Three GIBBERELLIN-INSENSITIVE DWARF2 Homologous Genes in Common Wheat.

F-box protein is a core component of the ubiquitin E3 ligase SCF complex and is involved in the gibberellin (GA) signaling pathway. To elucidate the molecular mechanism of GA signaling in wheat, three homologous GIBBERELLIN-INSENSITIVE DWARF2 genes, TaGID2s, were isolated from the Chinese Spring wheat variety. A subcellular localization assay in onion epidermal cells and Arabidopsis mesophyll protoplasts showed that TaGID2s are localized in the nuclei. The expression profiles using quantitative real-time polymerase chain reaction showed that TaGID2s were downregulated by GA3. The interaction between TaGID2s and TSK1 (homologous to ASK1) in yeast indicated that TaGID2s might function as a component of an E3 ubiquitin-ligase SCF complex. Yeast two-hybrid assays showed that a GA-independent interaction occurred between three TaGID2s and RHT-A1a, RHT-B1a, and RHT-D1a. Furthermore, TaGID2s interact with most RHT-1s, such as RHT-B1h, RHT-B1i, RHT-D1e, RHT-D1f, etc., but cannot interact with RHT-B1b or RHT-B1e, which have a stop codon in the DELLA motif, resulting in a lack of a GRAS domain. In addition, RHT-B1k has a frame-shift mutation in the VHIID motif leading to loss of the LHRII motif in the GRAS domain and RHT-D1h has a missense mutation in the LHRII motif. These results indicate that TaGID2s, novel positive regulators of the GA response, recognize RHT-1s in the LHRII motif resulting in poly-ubiquitination and degradation of the DELLA protein.