GA Synthesis Research Articles

Overexpression of the KNOX gene Tkn4 affects pollen development and confers sensitivity to gibberellin and auxin in tomato

The knotted1-like homeobox genes not only regulate the formation and differentiation of meristems and vascular system but are also involved in biosynthesis and signal transduction of diverse plant hormones in tomato. Here, we showed that a knotted1-like homeobox gene Tkn4 is required for pollen and pollen tube growth when this gene is overexpressed in tomato. Pollen grains in the Tkn4 overexpressed plants (Tkn4-OX) germinated quicker than those in the wild-type (WT) plant cultured in vitro in germination media. The percentage of fruit set was higher in Tkn4-OX than in WT plants and the transgenic plants showed an ordered inflorescence. Tkn4-OX seedlings also exhibited sensitivity to gibberellins (GA) and auxins. RNA sequencing results showed that the expression of genes related to sugar, cell wall-modification, microtubule-associated vesicular transport for pollen growth, GA and auxin synthesis were significantly changed. Hence, Tkn4 contributes to a function in the development of pollen and pollen tube and the regulation of phytohormones to participate in plant growth. These results provided a potential application value for agricultural improvement to enhance the rate of fruit set in tomato.

Exogenous brassinosteroids altered cell length, gibberellin content, and cellulose deposition in promoting carrot petiole elongation

Brassinosteroid (BR) is a predominant plant hormone in regulating cell elongation and cell size. BR-deficient mutants display reduced plant growth and dwarfism in Arabidopsis and rice. In carrot, BRs promote petiole elongation, but its underlying mechanism involving exogenous BR remains unknown. Here, weighted gene co-expression network analysis and promoter region analysis were adopted to identify the potential genes that interacted with DcBZR1/BES1. Bioactive gibberellin (GA) level and cellulose deposition were also determined in the control and treated plants. Quantitative real-time PCR was performed to detect the expression profiles of GA biosynthesis-related genes, GA signaling genes, and cellulose synthase genes. Bioactive GA level and cellulose deposition were upregulated after the petioles were treated with 24-epibrassinolide (24-EBL). The most putative DcBZR1/BES1 genes were clustered in yellow module. The expression level of DCAR_009411 (a GA5-like gene) was significantly induced after 3 h of treatment. The expression levels of DCAR_019754 and DCAR_013973 (CESA-like genes) were also significantly induced after 3 h of 24-EBL treatment. Our results suggested that the effect of BR on carrot petiole growth was quick. These results also provided potential insights into the mechanism by which BRs modulate GA and cellulose synthesis to promote cell elongation in carrot petioles.

Comprehensive Analysis of Cucumber Gibberellin Oxidase Family Genes and Functional Characterization of CsGA20ox1 in Root Development in Arabidopsis.

Cucumber (Cucumis sativus L.) is an important vegetable crop worldwide and gibberellins (GAs) play important roles in the regulation of cucumber developmental and growth processes. GA oxidases (GAoxs), which are encoded by different gene subfamilies, are particularly important in regulating bioactive GA levels by catalyzing the later steps in the biosynthetic pathway. Although GAoxs are critical enzymes in GA synthesis pathway, little is known about GAox genes in cucumber, in particular about their evolutionary relationships, expression profiles and biological function. In this study, we identified 17 GAox genes in cucumber genome and classified them into five subfamilies based on a phylogenetic tree, gene structures, and conserved motifs. Synteny analysis indicated that the tandem duplication or segmental duplication events played a minor role in the expansion of cucumber GA2ox, GA3ox and GA7ox gene families. Comparative syntenic analysis combined with phylogenetic analysis provided deep insight into the phylogenetic relationships of CsGAox genes and suggested that protein homology CsGAox are closer to AtGAox than OsGAox. In addition, candidate transcription factors BBR/BPC (BARLEY B RECOMBINANT/BASIC PENTACYSTEINE) and GRAS (GIBBERELLIC ACID-INSENSITIVE, REPRESSOR of GAI, and SCARECROW) which may directly bind promoters of CsGAox genes were predicted. Expression profiles derived from transcriptome data indicated that some CsGAox genes, especially CsGA20ox1, are highly expressed in seedling roots and were down-regulated under GA3 treatment. Ectopic over-expression of CsGA20ox1 in Arabidopsis significantly increased primary root length and lateral root number. Taken together, comprehensive analysis of CsGAoxs would provide a basis for understanding the evolution and function of the CsGAox family.

One-pot two-strain system based on glucaric acid biosensor for rapid screening of myo-inositol oxygenase mutations and glucaric acid production in recombinant cells

The development of D-glucaric acid (GA) production in recombinant cells has leapt forward in recent years, and higher throughput screening and selection of better-performing recombinant cells or biocatalysts is in current demand. A biosensor system which converts GA concentration into fluorescence signal in Escherichia coli was developed in 2016, but its application has rarely been reported. Herein, an effective high-throughput screening approach independent of special-purpose devices such as microfluidic platforms was established and tentatively applied. In this one-pot two-strain system, GA producers—bacterial or yeast cells containing the GA biosynthetic pathway—were sorted with the help of another E. coli strain acting as a GA biosensor. The identification of highly active mutants of myo-inositol oxygenase through this system validates its effectiveness in sorting E. coli cells. Subsequently, accurate ranking of the GA synthesis capacity of a small library of Saccharomyces cerevisiae strains containing distinct GA synthesis pathways demonstrated that this optimized one-pot two-strain system may also be used for eukaryotic producer strains. These results will assist in research into metabolic engineering for GA production and development of biosensor applications.

Identification and physiological function analysis of a new dwarf spikelet <italic>Dwarf18</italic>-allele mutant in rice

Plant height and panicle architecture are closely related agronomic traits that determine rice yield. In this study, a genetically stable dwarf spikelet mutant was isolated from the japonica cultivar “Taipei 309” through ethyl methanesulfonate mutagenesis. The mutant is mainly characterized by dwarfing, long grains, small width, and small panicle architecture. Genetic analysis revealed that the mutant phenotype was controlled by a single recessive nuclear gene, which was mapped to a 20-kb region between indel markers P4 and P5 on chromosome 1. Only one dwarf gene, Dwarf18 ( D18 ), has been cloned in this region, which encodes gibberellin 3β-hydroxylase (GA3ox2), suggesting that the mutant gene and D18 may be allelic. Sequence analysis of the mutant gene revealed the deletion of one base (G) in the second exon, causing a nonsense mutation. Quantitative real-time PCR results indicated that OsGA3ox2 expression in the mutant was significantly decreased. Therefore, we tentatively named the mutant gene “ d18-1 .” Tissue section observation revealed the mutant showed a markedly decreased length of longitudinal cells but an increased number of cells in the stem compared with the wild-type. A physiological function analysis revealed that the mutant was more sensitive to GA treatment but less sensitive to BR treatment than the wild-type. Expression analysis of genes related to GA and BR biosyntheses and signal transduction pathways revealed that GA-inactivating gene OsGA2ox3 and GA biosynthesis-related genes OsGA20ox2 and OsGA3ox2 were downregulated in the mutant; however, there were no significant differences in the expression of the key genes involved in the GA signaling pathway. In addition, downregulation was observed in most of the genes involved in the biosynthesis and signal transduction of BR in the mutant. These results indicate that the dwarf phenotype observed in the mutant was caused by abnormal GA synthesis and further impairment of the response pathway to exogenously active BR, resulting in a low-sensitivity response to BR. In addition, the microarray analysis of the wild-type and mutant panicles at the booting stage detected 1497 differentially expressed genes involved in phenylpropanoid biosynthesis and carbohydrate and carbon metabolisms. Therefore, the nonsense mutation of the OsGA3ox2 gene in the mutant was considered to affect the regulation of GA and BR biosyntheses and signal transduction pathways as well as panicle architecture development. This study provides new information for further research into the regulation of rice dwarfing and the genetic network of panicle architecture.

Optimal Selective Arbitrary-Spaced Filters Optimization Using GA Synthesis in One-Dimensional Silicon Photonic Crystal

The optimization process is a necessary step in the design of optimal optical devices with high performances. In this paper, optimization of unidirectional photonic crystal selective arbitrary-spaced filters based on silicon Material Si with large refractive index (n = 3.5) are achieved based on the genetic algorithm technique. The photonic crystal transmission synthesis is obtained by acting on the layer widths. Genetic algorithm is employed in order to reduce the quadratic error between the desired Gaussian function defined in advance and the synthesized power transmission spectra to obtain a desired curve and get the optimal filter layer thickness. As a result, eight filters have been synthesized around respectively the wavelengths: 1.1, 1.2, 1.3, 1.4, 1.55, 1.65, 1.75 and 1.95 μm with excellent selectivity and rejection less than 18% with a transmitted bandwidth of about 0.05 μm where a transmission of about 95% is recorded at the desired wavelengths.

Interplay between cytochrome c and gibberellins during Arabidopsis vegetative development.

We studied the effect of reducing the levels of the mitochondrial electron carrier cytochrome c (CYTc) in Arabidopsis thaliana. Plants with CYTc deficiency have delayed growth and development, and reach flowering several days later than the wild-type but with the same number of leaves. CYTc-deficient plants accumulate starch and glucose during the day, and contain lower levels of active gibberellins (GA) and higher levels of DELLA proteins, involved in GA signaling. GA treatment abolishes the developmental delay and reduces glucose accumulation in CYTc-deficient plants, which also show a lower raise in ATP levels in response to glucose. Treatment of wild-type plants with inhibitors of mitochondrial energy production limits plant growth and increases the levels of DELLA proteins, thus mimicking the effects of CYTc deficiency. In addition, an increase in the amount of CYTc decreases DELLA protein levels and expedites growth, and this depends on active GA synthesis. We conclude that CYTc levels impinge on the activity of the GA pathway, most likely through changes in mitochondrial energy production. In this way, hormone-dependent growth would be coupled to the activity of components of the mitochondrial respiratory chain.

Genetic Regulation of GA Metabolism during Vernalization, Floral Bud Initiation and Development in Pak Choi (Brassica rapa ssp. chinensis Makino).

Pak choi (Brassica rapa ssp. chinensis Makino) is a representative seed vernalization vegetable and premature bolting in spring can cause significant economic loss. Thus, it is critical to elucidate the mechanism of molecular regulation of vernalization and floral bud initiation to prevent premature bolting. Gibberellin (GA) is the key plant hormone involved in regulating plant development. To gain a better understanding of GA metabolism in pak choi, the content of GA in pak choi was measured at different stages of plant development using enzyme-linked immunosorbent assay. The results showed that the GA content increased significantly after low-temperature treatment (4°C) and then decreased rapidly with vegetative growth. During floral bud initiation, the GA content increased rapidly until it peaked upon floral bud differentiation. To elucidate these changes in GA content, the expression of homologous genes encoding enzymes directly involved in GA metabolism were analyzed. The results showed that the changes in the expression of four genes involved in GA synthesis (Bra035120 encoding ent-kaurene synthase, Bra009868 encoding ent-kaurene oxidase, Bra015394 encoding ent-kaurenoic acid oxidase, and Bra013890 encoding GA20-oxidase) were correlated with the changes in GA content. In addition, by comparing the expression of genes involved in GA metabolism at different growth stages, seven differentially expressed genes (Bra005596, Bra009285, Bra022565, Bra008362, Bra033324, Bra010802, and Bra030500) were identified. The differential expression of these genes were directly correlated with changes in GA content, suggesting that these genes were directly related to vernalization, floral bud initiation and development. These results contribute to the understanding of the molecular mechanism of changes in GA content during different developmental phases in pak choi.

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.

Temperature signals in seed germination.

Plant Biology The switch between seed dormancy and germination in Arabidopsis thaliana is regulated by the balance between the hormones abscisic acid (ABA) and gibberellin (GA). Low temperatures are known to cause an increase in GA synthesis and receptor abundance, thereby increasing the probability of germination. Topham et al. studied the integration of temperature signals and determined that the embryo radicle is enriched for factors involved in hormone signaling, synthesis, and degradation. A clear spatial pattern emerged whereby ABA and GA pathway components were broadly separated into different cell types. This spatial separation and control over transport of hormones between cells facilitates processing of fluctuating temperature inputs and increases their propensity to break seed dormancy, compared with signals from continuous cold exposure. This is hypothesized to ensure accurate timing of seedling establishment through recognition of environmental temperature oscillations. Proc. Natl. Acad. Sci. U.S.A. 10.1073/pnas.1704745114 (2017).

Spatiotemporal modulation of abscisic acid and gibberellin metabolism and signalling mediates the effects of suboptimal and supraoptimal temperatures on seed germination in wheat (Triticum aestivum L.).

Seed germination is a complex process regulated by intrinsic hormonal cues such as abscisic acid (ABA) and gibberellin (GA), and environmental signals including temperature. Using pharmacological, molecular and metabolomics approaches, we show that supraoptimal temperature delays wheat seed germination through maintaining elevated embryonic ABA level via increased expression of ABA biosynthetic genes (TaNCED1 and TaNCED2), increasing embryo ABA sensitivity through upregulation of genes regulating ABA signalling positively (TaPYL5, TaSnRK2, ABI3 and ABI5) and decreasing embryo GA sensitivity via induction of TaRHT1 that regulates GA signalling negatively. Endospermic ABA and GA appeared to have minimal roles in regulating germination at supraoptimal temperature. Germination inhibition by suboptimal temperature is associated with elevated ABA level in the embryo and endosperm tissues, mediated by induction of TaNCEDs and decreased expression of endospermic ABA catabolic genes (TaCYP707As), and increased ABA sensitivity in both tissues via upregulation of TaPYL5, TaSnRK2, ABI3 and ABI5 in the embryo and TaSnRK2 and ABI5 in the endosperm. Furthermore, suboptimal temperature suppresses GA synthesis in both tissues and GA sensitivity in the embryo via repressing GA biosynthetic genes (TaGA20ox and TaGA3ox2) and inducing TaRHT1, respectively. These results highlight that spatiotemporal modulation of ABA and GA metabolism and signalling in wheat seeds underlies germination response to temperature.

Gibberellin stimulates regrowth after defoliation of sheepgrass (Leymus chinensis) by regulating expression of fructan-related genes.

Gibberellins (GAs) affect forage growth and development; however, it is largely unknown how GAs regulate the metabolism of fructan (an important polysaccharide reserve in many cereals) and the regrowth of forage plants after defoliation. To explore the mechanism of the responses of defoliated sheepgrass [Leymus chinensis (Trin.) Tzvel] to GA, we sprayed defoliated sheepgrass with GA3 and/or paclobutrazol (PAC; an inhibitor of GA biosynthesis) and analyzed the growth characteristics, carbohydrate contents, and transcript levels of genes related to GA metabolism, GA signal transduction, and fructan metabolism. The results showed that spraying exogenous GA3 onto defoliated sheepgrass promoted leaf and internode elongation, while spraying with PAC inhibited leaf and internode elongation, compared with the control. Spraying GA3 onto defoliated sheepgrass also altered the fructan content by extending the period of fructan utilization. At the transcriptional level, exogenous GA3 increased the transcript levels of genes related to GA metabolism in the sheath. Taken together, our results suggest that exogenous GA3 stimulates the regrowth of defoliated sheepgrass regrowth by regulating GA and fructan-related genes, and by promoting endogenous GA synthesis, fructan metabolism, and signaling.

Re-induction of the cell cycle in the Arabidopsis post-embryonic root meristem is ABA-insensitive, GA-dependent and repressed by KRP6.

Seeding establishment following seed germination requires activation of the root meristem for primary root growth. We investigated the hormonal and genetic regulation of root meristem activation during Arabidopsis seed germination. In optimal conditions, radicle cell divisions occur only after the completion of germination and require de novo GA synthesis. When the completion of germination is blocked by ABA, radicle elongation and cell divisions occurred in these non-germinating seeds. Conversely under GA-limiting conditions, ABA-insensitive mutants complete germination in the absence of radicle meristem activation and growth. Radicle meristem activation and extension can therefore occur independently of completion of the developmental transition of germination. The cell cycle regulator KRP6 partially represses GA-dependent activation of the cell cycle. Germination of krp6 mutant seeds occurs more rapidly, is slightly insensitive to ABA in dose-response assays, but also hypersensitive to the GA synthesis inhibitor PAC. These conflicting phenotypes suggest the cell cycle uncouples GA and ABA responses in germinating Arabidopsis seeds, and that KRP6 acts downstream of GA to inhibit mitotic cell cycle activation during germination.

Gibberellin reactivates and maintains ovary-wall cell division causing fruit set in parthenocarpic Citrus species

Citrus is a wide genus in which most of the cultivated species and cultivars are natural parthenocarpic mutants or hybrids (i.e. orange, mandarin, tangerine, grapefruit). The autonomous increase in GA1 ovary concentration during anthesis was suggested as being the stimulus responsible for parthenocarpy in Citrus regardless of the species. To determine the exact GA-role in parthenocarpic fruit set, the following hypothesis was tested: GA triggers and maintains cell division in ovary walls causing fruit set. Obligate and facultative parthenocarpic Citrus species were used as a model system because obligate parthenocarpic Citrus sp (i.e. Citrus unshiu) have higher GA levels and better natural parthenocarpic fruit set compared to other facultative parthenocarpic Citrus (i.e. Citrus clementina).The autonomous activation of GA synthesis in C. unshiu ovary preceded cell division and CYCA1.1 up-regulation (a G2-stage cell cycle regulator) at anthesis setting a high proportion of fruits, whereas C. clementina lacked this GA-biosynthesis and CYCA1.1 up-regulation failing in fruit set. In situ hybridization experiments revealed a tissue-specific expression of GA20ox2 only in the dividing tissues of the pericarp. Furthermore, CYCA1.1 expression correlated endogenous GA1 content with GA3 treatment, which stimulated cell division and ovary growth, mostly in C. clementina. Instead, paclobutrazol (GA biosynthesis inhibitor) negated cell division and reduced fruit set.Results suggest that in parthenocarpic citrus the specific GA synthesis in the ovary walls at anthesis triggers cell division and, thus, the necessary ovary growth rate to set fruit.

An Endosperm-Associated Cuticle Is Required for Arabidopsis Seed Viability, Dormancy and Early Control of Germination.

Cuticular layers and seeds are prominent plant adaptations to terrestrial life that appeared early and late during plant evolution, respectively. The cuticle is a waterproof film covering plant aerial organs preventing excessive water loss and protecting against biotic and abiotic stresses. Cutin, consisting of crosslinked fatty acid monomers, is the most abundant and studied cuticular component. Seeds are dry, metabolically inert structures promoting plant dispersal by keeping the plant embryo in an arrested protected state. In Arabidopsis thaliana seeds, the embryo is surrounded by a single cell endosperm layer itself surrounded by a seed coat layer, the testa. Whole genome analyses lead us to identify cutin biosynthesis genes as regulatory targets of the phytohormones gibberellins (GA) and abscisic acid (ABA) signaling pathways that control seed germination. Cutin-containing layers are present in seed coats of numerous species, including Arabidopsis, where they regulate permeability to outer compounds. However, the role of cutin in mature seed physiology and germination remains poorly understood. Here we identify in mature seeds a thick cuticular film covering the entire outer surface of the endosperm. This seed cuticle is defective in cutin-deficient bodyguard1 seeds, which is associated with alterations in endospermic permeability. Furthermore, mutants affected in cutin biosynthesis display low seed dormancy and viability levels, which correlates with higher levels of seed lipid oxidative stress. Upon seed imbibition cutin biosynthesis genes are essential to prevent endosperm cellular expansion and testa rupture in response to low GA synthesis. Taken together, our findings suggest that in the course of land plant evolution cuticular structures were co-opted to achieve key physiological seed properties.

Divergence and adaptive evolution of the gibberellin oxidase genes in plants.

BackgroundThe important phytohormone gibberellins (GAs) play key roles in various developmental processes. GA oxidases (GAoxs) are critical enzymes in GA synthesis pathway, but their classification, evolutionary history and the forces driving the evolution of plant GAox genes remain poorly understood.ResultsThis study provides the first large-scale evolutionary analysis of GAox genes in plants by using an extensive whole-genome dataset of 41 species, representing green algae, bryophytes, pteridophyte, and seed plants. We defined eight subfamilies under the GAox family, namely C19-GA2ox, C20-GA2ox, GA20ox,GA3ox, GAox-A, GAox-B, GAox-C and GAox-D. Of these, subfamilies GAox-A, GAox-B, GAox-C and GAox-D are described for the first time. On the basis of phylogenetic analyses and characteristic motifs of GAox genes, we demonstrated a rapid expansion and functional divergence of the GAox genes during the diversification of land plants. We also detected the subfamily-specific motifs and potential sites of some GAox genes, which might have evolved under positive selection.ConclusionsGAox genes originated very early—before the divergence of bryophytes and the vascular plants and the diversification of GAox genes is associated with the functional divergence and could be driven by positive selection. Our study not only provides information on the classification of GAox genes, but also facilitates the further functional characterization and analysis of GA oxidases.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-015-0490-2) contains supplementary material, which is available to authorized users.

Antagonistic action of blue and red light on shoot elongation in petunia depends on gibberellin, but the effects on flowering are not generally linked to gibberellin

Plant morphology and flowering are influenced by light quality, but responses vary between species. Here we investigated effects of irradiance (70 or 150μmolm−2s−1) of red (R) and blue (B) compared to white (W) light, provided by light emitting diodes, on growth and flowering in petunia. R light inhibited shoot elongation, but opposite to commonly observed, B light greatly enhanced shoot elongation. Consistent with this, bioactive gibberellins (GA1, GA4) showed higher and lower levels under B and R light, respectively, and GA3 application induced elongation in uniconazole-treated plants, although delayed in R. Inhibited shoot elongation under RB treatment in spite of higher GA level compared to R only, supports that R light inhibits elongation growth, and indicates negative effect of R light on GA signaling. Floral bud formation and flowering occurred earlier under B compared to W light. Whereas no floral buds were observed under low R irradiance, high R irradiance and temporal switching to B light during long-term low R irradiance induced floral development. Except slight trends of promoting effect of the highest GA3 level and delay in uniconazole-response under B light, lack of flowering under low R irradiance was not significantly affected by uniconazole or GA3 application. In conclusion, B and R light are strong signals enhancing and inhibiting shoot elongation, respectively, through modulation of GA content. B light is a strong signal in floral bud formation, whereas effect of R light depends on irradiance, indicating existence of an energy/photosynthesis-related floral pathway in petunia. Although light quality affects flowering and main shoot elongation, these responses do probably not correlate with each other through GA synthesis.

Transcriptome profiling reveals the regulatory mechanism underlying pollination dependent and parthenocarpic fruit set mainly mediated by auxin and gibberellin.

BackgroundFruit set is a key process for crop production in tomato which occurs after successful pollination and fertilization naturally. However, parthenocarpic fruit development can be uncoupled from fertilization triggered by exogenous auxin or gibberellins (GAs). Global transcriptome knowledge during fruit initiation would help to characterize the molecular mechanisms by which these two hormones regulate pollination-dependent and -independent fruit set.Principal FindingsIn this work, digital gene expression tag profiling (DGE) technology was applied to compare the transcriptomes from pollinated and 2, 4-D/GA3-treated ovaries. Activation of carbohydrate metabolism, cell division and expansion as well as the down-regulation of MADS-box is a comprehensive regulatory pathway during pollination-dependent and parthenocarpic fruit set. The signaling cascades of auxin and GA are significantly modulated. The feedback regulations of Aux/IAAs and DELLA genes which functioned to fine-tune auxin and GA response respectively play fundamental roles in triggering fruit initiation. In addition, auxin regulates GA synthesis via up-regulation of GA20ox1 and down-regulation of KNOX. Accordingly, the effect of auxin on fruit set is mediated by GA via ARF2 and IAA9 down-regulation, suggesting that both pollination-dependent and parthenocarpic fruit set depend on the crosstalk between auxin and GA.SignificanceThis study characterizes the transcriptomic features of ovary development and more importantly unravels the integral roles of auxin and GA on pollination-dependent and parthenocarpic fruit set.

Maximizing carbon efficiency of petrochemical production from catalytic co-pyrolysis of biomass and plastics using gallium-containing MFI zeolites

A series of gallium-containing MFI zeolites were prepared via impregnation of conventional aluminosilicate ZSM-5 with Ga (Ga/ZSM-5) or hydrothermal synthesis of galloaluminosilicate (Ga–Al–Si) and gallosilicate (Ga–Si) MFI zeolites. These Ga-containing zeolites were then tested as the catalysts for co-feed catalytic fast pyrolysis (CFP) of pine wood and low-density polyethylene (LDPE) mixtures. Compared with conventional ZSM-5 zeolites, the Ga-containing MFI zeolites considerably increased the yields of valuable petrochemicals (monoaromatic hydrocarbons and olefins) and decreased the yields of undesired polyaromatic hydrocarbons and low-value alkanes from the co-feed CFP. In addition, Ga–Al–Si and Ga–Si zeolites generally produced both higher yields and selectivities for valuable petrochemicals (e.g., p-xylene and olefins) than Ga/ZSM-5 in the co-feed CFP. The results indicate that Ga-containing zeolites may be used to improve petrochemical production in co-feed CFP of biomass and plastics, and direct hydrothermal synthesis of Ga–Al–Si and Ga–Si MFI zeolites may provide a more convenient and better alternative to post modification of ZSM-5 with Ga to prepare Ga-containing zeolites for co-feed CFP.

Gibberellins interfere with symbiosis signaling and gene expression and alter colonization by arbuscular mycorrhizal fungi in Lotus japonicus.

Arbuscular mycorrhiza is a mutualistic plant-fungus interaction that confers great advantages for plant growth. Arbuscular mycorrhizal (AM) fungi enter the host root and form symbiotic structures that facilitate nutrient supplies between the symbionts. The gibberellins (GAs) are phytohormones known to inhibit AM fungal infection. However, our transcriptome analysis and phytohormone quantification revealed GA accumulation in the roots of Lotus japonicus infected with AM fungi, suggesting that de novo GA synthesis plays a role in arbuscular mycorrhiza development. We found pleiotropic effects of GAs on the AM fungal infection. In particular, the morphology of AM fungal colonization was drastically altered by the status of GA signaling in the host root. Exogenous GA treatment inhibited AM hyphal entry into the host root and suppressed the expression of Reduced Arbuscular Mycorrhization1 (RAM1) and RAM2 homologs that function in hyphal entry and arbuscule formation. On the other hand, inhibition of GA biosynthesis or suppression of GA signaling also affected arbuscular mycorrhiza development in the host root. Low-GA conditions suppressed arbuscular mycorrhiza-induced subtilisin-like serine protease1 (SbtM1) expression that is required for AM fungal colonization and reduced hyphal branching in the host root. The reduced hyphal branching and SbtM1 expression caused by the inhibition of GA biosynthesis were recovered by GA treatment, supporting the theory that insufficient GA signaling causes the inhibitory effects on arbuscular mycorrhiza development. Most studies have focused on the negative role of GA signaling, whereas our study demonstrates that GA signaling also positively interacts with symbiotic responses and promotes AM colonization of the host root.