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The mechanism underlying seed germination promotion by plant growth-promoting rhizobacteria (PGPR) remains unclear. This study investigated the effects of Bacillus subtilis QM3 (a PGPR) and gibberellic acid (GA3) on germination indexes, seedling growth, and amylase activity in wheat seeds (Triticum aestivum L.) (caryopses) at different germination times. The results showed that B. subtilis QM3 exhibited a significantly greater increase in most measured indicators compared to GA3 (p < 0.05), and the coordinated effect of bacteria QM3 and GA3 was superior. GA3 showed no promotion of radicle length (LR) from day 3 to day 7. Conversely, the addition of uniconazole (U), a gibberellin synthesis inhibitor, significantly reduced all indexes except for fresh weight (FW) and root-shoot ratio (RSR). However, both B. subtilis QM3 and GA3 significantly alleviated the inhibition (p < 0.05), especially in the germination rate and amylase activity. The gibberellin (GA) content and expression of two key biosynthetic enzyme genes were also characterized. Further investigations revealed that the GA content in the B. subtilis QM3 group was significantly higher than in the control group at 12 h, 24 h, and 48 h during seed germination (p < 0.05). Moreover, B. subtilis QM3 significantly increased TaGA3ox-B2 expression (p < 0.05), with 1.44 times that of the control group, while there was no significant effect on TaGA20ox-D2 expression. Furthermore, amylase activity was positively correlated with the germination rate (GR) and GA content was positively correlated with amylase activity according to Pearson's correlation analysis, with R2 values of 0.8102 and 0.8365, respectively. Our results demonstrate that one of the mechanisms by which B. subtilis QM3 promotes wheat seed germination may be the induction of GA biosynthesis. [ABSTRACT FROM AUTHOR]

Histone acetyltransferases (HATs) modify the amino-terminal tails of the core histone proteins via acetylation, regulating chromatin structure and transcription. GENERAL CONTROL NON-DEREPRESSIBLE 5 (GCN5) is a HAT that specifically acetylates H3K14 residues. GCN5 has been associated with cell division and differentiation, meristem function, root, stem, foliar, and floral development, and plant environmental response. The flowers of gcn5 plants display a reduced stamen length and exhibit male sterility relative to the wild-type plants. We show that these effects may arise from gibberellin (GA)-signaling defects. The signaling pathway of bioactive GAs depends on the proteolysis of their repressors, DELLA proteins. The repressor GA (RGA) DELLA protein represses plant growth, inflorescence, and flower and seed development. Our molecular data indicate that GCN5 is required for the activation and H3K14 acetylation of genes involved in the late stages of GA biosynthesis and catabolism. We studied the genetic interaction of the RGA and GCN5; the RGA can partially suppress GCN5 action during the whole plant life cycle. The reduced elongation of the stamen filament of gcn5–6 mutants is reversed in the rga–t2;gcn5–6 double mutants. RGAs suppress the GCN5 effect on the gene expression and histone acetylation of GA catabolism and GA signaling. Interestingly, the RGA and RGL2 do not suppress ADA2b function, suggesting that ADA2b acts downstream of GA signaling and is distinct from GCN5 activity. In conclusion, we propose that the action of GCN5 on stamen elongation is partially mediated by RGA and GA signaling. [ABSTRACT FROM AUTHOR]

Abstracts: As the ‘Green Revolution’ gene, SD1 (encoding GA20ox2), has been widely applied to improve yield in rice breeding. However, research on its transcriptional regulation is limited. Here, we identified a transcription factor OsbZIP01, which can suppress the expression of SD1 and regulate gibberellin (GA) biosynthesis in rice. Knockout mutants of OsbZIP01 exhibited increased plant height, while the over- expression lines showed a semi-dwarf phenotype and diminished germination rate. Furthermore, the semi-dwarf phenotype of OE-bZIP01, was caused by the reduced internode length, which was accompanied by a thin stem width. The predominant expression of OsbZIP01 was observed in leaves and sheaths. OsbZIP01 protein was localized in the nucleus and showed transcriptional repression activity. In addition, OsbZIP01 could directly bind to the promoter of the OsSD1 gene, and inhibit its transcription. The semi-dwarf phenotype of OE-bZIP01 could be rescued by exogenous GA3. Meanwhile, the bzip01 sd1 double mutant showed a shorter shoot length compared with the wild type, indicating that OsbZIP01 regulated plant growth mainly through the GA biosynthesis pathway. Collectively, OsbZIP01 negatively regulates GA biosynthesis by restraining SD1 transcription, thereby affecting plant growth and development.

As the 'Green Revolution' gene, SD1 (encoding GA20ox2), has been widely applied to improve yield in rice breeding. However, research on its transcriptional regulation is limited. Here, we identified a transcription factor OsbZIP01, which can suppress the expression of SD1 and regulate gibberellin (GA) biosynthesis in rice. Knockout mutants of OsbZIP01 exhibited increased plant height, while the over- expression lines showed a semi-dwarf phenotype and diminished germination rate. Furthermore, the semi-dwarf phenotype of OE - bZIP01 , was caused by the reduced internode length, which was accompanied by a thin stem width. The predominant expression of OsbZIP01 was observed in leaves and sheaths. OsbZIP01 protein was localized in the nucleus and showed transcriptional repression activity. In addition, OsbZIP01 could directly bind to the promoter of the OsSD1 gene, and inhibit its transcription. The semi-dwarf phenotype of OE - bZIP01 could be rescued by exogenous GA 3. Meanwhile, the bzip01 sd1 double mutant showed a shorter shoot length compared with the wild type, indicating that OsbZIP01 regulated plant growth mainly through the GA biosynthesis pathway. Collectively, OsbZIP01 negatively regulates GA biosynthesis by restraining SD1 transcription, thereby affecting plant growth and development. [ABSTRACT FROM AUTHOR]

Background. Gibberellins (GAs) play important roles in regulating peanut growth and development. GA20ox and GA3ox are key enzymes involved in GA biosynthesis. These enzymes encoded by a multigene family belong to the 2OG-Fe (II) oxygenase superfamily. To date, no genome-wide comparative analysis of peanut AhGA20ox and AhGA3ox-encoding genes has been performed, and the roles of these genes in peanut pod development are not clear. Methods.Awhole-genome analysis of AhGA20ox and AhGA3ox gene families in peanut was carried out using bioinformatic tools. The expression of these genes at different stage of pod development was analyzed using qRT-PCR. Results. In this study, a total of 15 AhGA20ox and five AhGA3ox genes were identified in peanut genome, which were distributed on 14 chromosomes. Phylogenetic analysis divided the GA20oxs and GA3oxs into three groups, but AhGA20oxs and AhGA3oxs in two groups. The conserved pattern of gene structure, cis-elements, and protein motifs further confirmed their evolutionary relationship in peanut. AhGA20ox and AhGA3ox genes were differential expressed at different stages of pod development. The strong expression of AhGA20ox1/AhGA20ox4, AhGA20ox12/AhGA20ox15, AhGA3ox1 and AhGA3ox4/AhGA3ox5 in S1-stage indicated that these genes could have a key role in controlling peg elongation. Furthermore, AhGA20ox and AhGA3ox also showed diverse expression patterns in different peanut tissues including leaves, main stems, flowers and inflorescences. Noticeably, AhGA20ox9/AhGA20ox11 and AhGA3o4/AhGA3ox5 were highly expressed in the main stem, whereas the AhGA3ox1 and AhGA20ox10 were strongly expressed in the inflorescence. The expression levels of AhGA20ox2/AhGA20ox3, AhGA20ox5/AhGA20ox6, AhGA20ox7/AhGA20ox8, AhGA20ox13/AhGA20ox14 and AhGA3ox2/AhGA3ox3 were high in the flowers, suggesting their involvement in flower development. These results provide a basis for deciphering the roles of AhGA20ox and AhGA3ox in peanut growth and development, especially in pod development. [ABSTRACT FROM AUTHOR]

The present study was aimed to assess the efficacy of foliar-applied uniconazole on flower induction, and fruit yield of mango cv. 'Dusehri' at Department of Fruit Science, Punjab Agricultural University, Ludhiana, India. The experiment was conducted simultaneously at two different locations, for two cropping seasons during 2019–20 (ON year) and 2020–21 (OFF year). The pre-flowering treatments of paclobutrazol and uniconazole were sprayed during September and October at different rates. Experimental plants were observed for various biochemical, vegetative, reproductive and yield parameters. According to the results, foliar application of uniconazole (T6) @ 1.0 g a.i/m canopy applied twice significantly enhanced chlorophyll, carbohydrates, and C:N ratio and negatively affected shoot growth, nitrogen content by inhibiting the gibberellin biosynthesis. Ultimately, uniconazole improved flowering, fruit retention, fruit yield, and fruit size in mango cv. 'Dusehri'. Therefore, the foliar application of uniconazole can be considered as a better alternative to paclobutrazol in flower induction of mango. [ABSTRACT FROM AUTHOR]

BACKGROUND: Ratoon rice cropping has been introduced for increased rice production in southern China and, as a result, has been becoming increasingly popular. However, only a few studies have addressed the regulatory mechanism underlying grain quality improvement induced by rice ratooning. RESULTS: In this study, parameters of rice quality, including head rice yield, chalky grain percentage, grain chalkiness degree, hardness and taste value, were shown to be much improved in the ratooning season rice as compared to its counterparts main and late cropping season rice, indicating that such an improvement was irrespective of seasonal effects. In addition, the nutritional components of grains varied greatly between main‐cropping season rice, ratooning season rice and late‐cropping season rice and displayed a significant correlation with rice quality. Finally, the regulatory mechanism underlying rice quality improvement revealed that gibberellin‐dominated regulation and plant hormone signal transduction jointly contributed to a decrease in formation of chalky grains. CONCLUSION: This work improves our knowledge on rice quality improvement under rice ratooning, particularly on the regulatory mechanism of plant hormones. © 2022 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Apple replant disease (ARD) is a worldwide economic risk in apple cultivation for fruit tree nurseries and fruit growers. Several studies on the reaction of apple plants to ARD are documented but less is known about the genetic mechanisms behind this symptomatology. RNA-seq analysis is a powerful tool for revealing candidate genes that are involved in the molecular responses to biotic stresses in plants. The aim of our work was to find differentially expressed genes in response to ARD in Malus. For this, we compared transcriptome data of the rootstock 'M9' (susceptible) and the wild apple genotype M. × robusta 5 (Mr5, tolerant) after cultivation in ARD soil and disinfected ARD soil, respectively. When comparing apple plantlets grown in ARD soil to those grown in disinfected ARD soil, 1,206 differentially expressed genes (DEGs) were identified based on a log2 fold change, (LFC) ≥ 1 for up– and ≤ −1 for downregulation (p < 0.05). Subsequent validation revealed a highly significant positive correlation (r = 0.91; p < 0.0001) between RNA-seq and RT-qPCR results indicating a high reliability of the RNA-seq data. PageMan analysis showed that transcripts of genes involved in gibberellic acid (GA) biosynthesis were significantly enriched in the DEG dataset. Most of these GA biosynthesis genes were associated with functions in cell wall stabilization. Further genes were related to detoxification processes. Genes of both groups were expressed significantly higher in Mr5, suggesting that the lower susceptibility to ARD in Mr5 is not due to a single mechanism. These findings contribute to a better insight into ARD response in susceptible and tolerant apple genotypes. However, future research is needed to identify the defense mechanisms, which are most effective for the plant to overcome ARD. [ABSTRACT FROM AUTHOR]

Apple replant disease (ARD) is a worldwide economic risk in apple cultivation for fruit tree nurseries and fruit growers. Several studies on the reaction of apple plants to ARD are documented but less is known about the genetic mechanisms behind this symptomatology. RNA-seq analysis is a powerful tool for revealing candidate genes that are involved in the molecular responses to biotic stresses in plants. The aim of our work was to find differentially expressed genes in response to ARD in Malus. For this, we compared transcriptome data of the rootstock ‘M9’ (susceptible) and the wild apple genotype M. ×robusta 5 (Mr5, tolerant) after cultivation in ARD soil and disinfected ARD soil, respectively. When comparing apple plantlets grown in ARD soil to those grown in disinfected ARD soil, 1,206 differentially expressed genes (DEGs) were identified based on a log2 fold change, (LFC) ≥ 1 for up– and ≤ −1 for downregulation (p

SUMMARY: Grain size is one of the essential components determining rice yield and is a target for both domestication and artificial breeding. Gibberellins (GAs) are diterpenoid phytohormones that influence diverse aspects of plant growth and development. Several quantitative trait loci (QTLs) have been identified that control grain size through phytohormone regulation. However, little is known about the role of GAs in the control of grain size. Here we report the cloning and characterization of a QTL, GW6 (GRAIN WIDTH 6), which encodes a GA‐regulated GAST family protein and positively regulates grain width and weight. GW6 is highly expressed in the young panicle and increases grain width by promoting cell expansion in the spikelet hull. Knockout of GW6 exhibits reduced grain size and weight, whereas overexpression of GW6 results in increased grain size and weight. GW6 is induced by GA and its knockout downregulates the expression of GA biosynthesis genes and decreases GA content in the young panicle. We found that a natural variation in the cis element CAAT‐box in the promoter of GW6 is associated with its expression level and grain width and weight. Furthermore, introduction of GW6 to Oryza indica variety HJX74 can lead to a 10.44% increase in rice grain yield, indicating that GW6 has great potential to improve grain yield in rice. Significance Statement: GW6 participates in the regulation of gibberellin biosynthesis in the rice panicle, by which it can positively regulate grain size and weight by promoting cell expansion in the spikelet hull and accelerating the grain filling rate, leading to a significant increase in grain yield. Therefore, GW6 has great potential to improve grain yield in rice breeding. [ABSTRACT FROM AUTHOR]

Highlights • Gibberellin deficiency increases the partition of reserves to the root compared to the shoot. • Impaired GAs biosynthesis lead to pronounced alterations in the primary metabolism, mainly following water limitation. • Water deficit elevates the amino acid content, especially proline, in leaves and roots of gibberellin biosynthesis mutant. • The lack of gibberellin promotes maintenance of the water content and thereby enhancing tolerance to the water deficit. Abstract Gibberellins (GAs) have been shown to be involved in the tolerance of plants to a range of environmental stresses. However, the physiological and metabolic implications of altered levels of GAs in plants under drought stress remain largely unknown. To understand the contribution of GAs for the responses to water deficit conditions, physiological and metabolic parameters were evaluated in tomato deficient mutants in GAs biosynthesis, gib1 , gib2 , and gib3. Interestingly, the mutants maintained leaf water content over a longer time period and recovered photosynthesis faster than wild-type (WT) plants. Furthermore, gib1 and gib2 plants showed no apparent wilt even after reaching low leaf water potential (-1.3 MPa). Additionally, mutants plants partitioned more biomass to the roots than shoots compared to WT. The maintenance of leaf water content and consequent increased water use efficiency observed in the mutants can be explained by the osmotic adjustment of leaf and root cells, mainly due to amino acid accumulation. Collectively, our results suggest that plants with reduced GAs content are able to cope with water deprivation by increasing proline and other amino acid levels. This response, alongside partitioning of carbon to roots allows GAs-deficient plants to maintain the leaf turgor for a longer time and thereby promotes water deficit tolerance. [ABSTRACT FROM AUTHOR]

In the current study, we aimed to elucidate the plant growth-promoting characteristics of Pseudomonas psychrotolerans CS51 under heavy metal stress conditions (Zn, Cu, and Cd) and determine the genetic makeup of the CS51 genome using the single-molecule real-time (SMRT) sequencing technology of Pacific Biosciences. The results revealed that inoculation with CS51 induced endogenous indole-3-acetic acid (IAA) and gibberellins (GAs), which significantly enhanced cucumber growth (root shoot length) and increased the heavy metal tolerance of cucumber plants. Moreover, genomic analysis revealed that the CS51 genome consisted of a circular chromosome of 5,364,174 base pairs with an average G+C content of 64.71%. There were around 4774 predicted protein-coding sequences (CDSs) in 4859 genes, 15 rRNA genes, and 67 tRNA genes. Around 3950 protein-coding genes with function prediction and 733 genes without function prediction were identified. Furthermore, functional analyses predicted that the CS51 genome could encode genes required for auxin biosynthesis, nitrate and nitrite ammonification, the phosphate-specific transport system, and the sulfate transport system, which are beneficial for plant growth promotion. The heavy metal resistance of CS51 was confirmed by the presence of genes responsible for cobalt-zinc-cadmium resistance, nickel transport, and copper homeostasis in the CS51 genome. The extrapolation of the curve showed that the core genome contained a minimum of 2122 genes (95% confidence interval = 2034.24 to 2080.215). Our findings indicated that the genome sequence of CS51 may be used as an eco-friendly bioresource to promote plant growth in heavy metal-contaminated areas.

Background: Gibberellins (GAs) play important roles in regulating peanut growth and development. GA20ox and GA3ox are key enzymes involved in GA biosynthesis. These enzymes encoded by a multigene family belong to the 2OG-Fe (II) oxygenase superfamily. To date, no genome-wide comparative analysis of peanut AhGA20ox and AhGA3ox -encoding genes has been performed, and the roles of these genes in peanut pod development are not clear., Methods: A whole-genome analysis of AhGA20ox and AhGA3ox gene families in peanut was carried out using bioinformatic tools. The expression of these genes at different stage of pod development was analyzed using qRT-PCR., Results: In this study, a total of 15 AhGA20ox and five AhGA3ox genes were identified in peanut genome, which were distributed on 14 chromosomes. Phylogenetic analysis divided the GA20oxs and GA3oxs into three groups, but AhGA20oxs and AhGA3oxs in two groups. The conserved pattern of gene structure, cis-elements, and protein motifs further confirmed their evolutionary relationship in peanut. AhGA20ox and AhGA3ox genes were differential expressed at different stages of pod development. The strong expression of AhGA20ox1/AhGA20ox4 , AhGA20ox12/AhGA20ox15 , AhGA3ox1 and AhGA3ox4/AhGA3ox5 in S1-stage indicated that these genes could have a key role in controlling peg elongation. Furthermore, AhGA20ox and AhGA3ox also showed diverse expression patterns in different peanut tissues including leaves, main stems, flowers and inflorescences. Noticeably, AhGA20ox9/AhGA20ox11 and AhGA3o4/AhGA3ox5 were highly expressed in the main stem, whereas the AhGA3ox1 and AhGA20ox10 were strongly expressed in the inflorescence. The expression levels of AhGA20ox2/AhGA20ox3 , AhGA20ox5/AhGA20ox6 , AhGA20ox7/AhGA20ox8 , AhGA20ox13/AhGA20ox14 and AhGA3ox2/AhGA3ox3 were high in the flowers, suggesting their involvement in flower development. These results provide a basis for deciphering the roles of AhGA20ox and AhGA3ox in peanut growth and development, especially in pod development., Competing Interests: The authors declare there are no competing interests., (©2023 Sun et al.)

1,2,6-Trideoxy-6-amido-d-allose derivative was synthesized and found to exhibit higher growth-inhibitory activity against plants than the corresponding deoxy-d-allose ester, which indicates that an amide group at C-6 of the deoxy-d-allose amide enhances inhibitory activity. In addition, the mode of action of the deoxy-d-allose amide was significantly different from that of d-allose which inhibits gibberellin signaling. Co-addition of gibberellin GA3 restored the growth of rice seedlings inhibited by the deoxy-d-allose amide, suggesting that it might inhibit biosynthesis of gibberellins in plants to induce growth inhibition. [ABSTRACT FROM AUTHOR]

Phytopathogens have developed elaborate mechanisms to attenuate the defense response of their host plants, including convergent evolution of complex pathways for production of the GA phytohormones, which were actually first isolated from the rice fungal pathogen Gibberella fujikuroi. The rice bacterial pathogen Xanthomonas oryzae pv. oryzicola (Xoc) has been demonstrated to contain a biosynthetic operon with cyclases capable of producing the universal GA precursor ent-kaurene. Genetic (knock-out) studies indicate that the derived diterpenoid serves as a virulence factor for this rice leaf streak pathogen, serving to reduce the jasmonic acid-mediated defense response., Here the functions of the remaining genes in the Xoc operon are elucidated and the distribution of the operon in X. oryzae is investigated in over 100 isolates., The Xoc operon leads to production of the bioactive GA4, an additional step beyond production of the penultimate precursor GA9 mediated by the homologous operons recently characterized from rhizobia. Moreover, this GA biosynthetic operon was found to be widespread in Xoc (> 90%), but absent in the other major X. oryzae pathovar., These results indicate selective pressure for production of GA4 in the distinct lifestyle of Xoc, and the importance of GA to both fungal and bacterial pathogens of rice. [ABSTRACT FROM AUTHOR]

The genus Fusarium, including multiple strains in the Gibberella fujikuroi species complex (GFC), is well known for its production of diverse secondary metabolites. F. fujikuroi, associated with the 'bakanae' disease of rice, is an active producer of gibberellins (GAs), a wide class of plant hormones. In addition to some members of the GFC, the GA biosynthetic gene cluster, or parts of it, occurs also in some isolates of the closely related species of F. oxysporum, which does not belong to the GFC. However, production of GAs has never been observed in any F. oxysporum strain. In this study, we report on the GA biosynthetic activity in an orchid-associated F. oxysporum strain by transforming a cosmid with the entire F. fujikuroi GA gene cluster. Southern and Northern blot analyses confirmed not only the integration of the entire gene cluster into the genome but also the active expression of the seven GA biosynthetic genes under nitrogen-limiting conditions. The transformants produced GAs at levels similar to those of F. fujikuroi. These data show that the regulatory network for expression of GA genes is fully active in the F. oxysporum background. [ABSTRACT FROM AUTHOR]

Gibberellin research has its origins in Japan in the 19th century, when a disease of rice was shown to be due to a fungal infection. The symptoms of the disease including overgrowth of the seedling and sterility were later shown to be due to secretions of the fungus Gibberella fujikuroi (now reclassified as Fusarium fujikuroi), from which the name gibberellin was derived for the active component. The profound effect of gibberellins on plant growth and development, particularly growth recovery in dwarf mutants and induction of bolting and flowering in some rosette species, prompted speculation that these fungal metabolites were endogenous plant growth regulators and this was confirmed by chemical characterisation in the late 1950s. Gibberellins are now known to be present in vascular plants, and some fungal and bacterial species. The biosynthesis of gibberellins in plants and the fungus has been largely resolved in terms of the pathways, enzymes, genes and their regulation. The proposal that gibberellins act in plants by removing growth limitation was confirmed by the demonstration that they induce the degradation of the growth-inhibiting DELLA proteins. The mechanism by which this is achieved was clarified by the identification of the gibberellin receptor from rice in 2005. Current research on gibberellin action is focussed particularly on the function of DELLA proteins as regulators of gene expression. This review traces the history of gibberellin research with emphasis on the early discoveries that enabled the more recent advances in this field. [ABSTRACT FROM AUTHOR]

Background: Labdane-related diterpenoids form the largest group among the diterpenes. They fulfill important functions in primary metabolism as essential plant growth hormones and are known to function in secondary metabolism as, for example, phytoalexins. The biosynthesis of labdane-related diterpenes is mediated by the action of class II and class I diterpene synthases. Although terpene synthases have been well investigated in poplar, little is known about diterpene formation in this woody perennial plant species. Results: The recently sequenced genome of Populus trichocarpa possesses two putative copalyl diphosphate synthase genes (CPS, class II) and two putative kaurene synthase genes (KS, class I), which most likely arose through a genome duplication and a recent tandem gene duplication, respectively. We showed that the CPS-like gene PtTPS17 encodes an ent-copalyl diphosphate synthase (ent-CPS), while the protein encoded by the putative CPS gene PtTPS18 showed no enzymatic activity. The putative kaurene synthases PtTPS19 and PtTPS20 both accepted ent-copalyl diphosphate (ent-CPP) as substrate. However, despite their high sequence similarity, they produced different diterpene products. While PtTPS19 formed exclusively ent-kaurene, PtTPS20 generated mainly the diterpene alcohol, 16α-hydroxy-ent-kaurane. Using homology-based structure modeling and site-directed mutagenesis, we demonstrated that one amino acid residue determines the different product specificity of PtTPS19 and PtTPS20. A reciprocal exchange of methionine 607 and threonine 607 in the active sites of PtTPS19 and PtTPS20, respectively, led to a complete interconversion of the enzyme product profiles. Gene expression analysis revealed that the diterpene synthase genes characterized showed organ-specific expression with the highest abundance of PtTPS17 and PtTPS20 transcripts in poplar roots. Conclusions: The poplar diterpene synthases PtTPS17, PtTPS19, and PtTPS20 contribute to the production of ent-kaurene and 16α-hydroxy-ent-kaurane in poplar. While ent-kaurene most likely serves as the universal precursor for gibberellins, the function of 16α-hydroxy-ent-kaurane in poplar is not known yet. However, the high expression levels of PtTPS20 and PtTPS17 in poplar roots may indicate an important function of 16α-hydroxy-ent-kaurane in secondary metabolism in this plant organ. [ABSTRACT FROM AUTHOR]

*Background and Aims The occurrence of Arabidopsis thaliana semi-dwarf accessions carrying inactive alleles at the gibberellin (GA) biosynthesis GA5 locus has raised the question whether there are pleiotropic effects on other traits at the root level, such as rooting depth. In addition, it is unknown whether semi-dwarfism in arabidopsis con fers a growth advantage under water-limiting conditions compared with wild-type plants. The aim of this research was therefore to investigate whether semi-dwarfism has a pleiotropic effect in the root system and also whether semi-dwarfs might be more tolerant of water-limiting conditions. *Methods The root systems of different arabidopsis semi-dwarfs and GA biosynthesis mutants were phenotyped in vitro using the GROWSCREEN-ROOT image-based software. Semi-dwarfs were phenotyped together with tall, near-related accessions. In addition, root phenotypes were investigated in soil-filled rhizotrons. Rosette growth tra jectories were analysed with the GROWSCREEN-FLUORO setup based on non-invasive imaging. *Key Results Mutations in the early steps of the GA biosynthesis pathway led to a reduction in shoot as well as root size. Depending on the genetic background, mutations at the GA5 locus yielded phenotypes characterized by decreased root length in comparison with related wild-type ones. The semi-dwarf accession Pak-3 showed the deep est root system both in vitro and in soil cultivation experiments; this comparatively deep root system, however, was independent of the ga5 loss-of-functionallele, as shown by co-segregation analysis. When the accessions were grown under water-limiting conditions, semi-dwarf accessions with high growth rates were identified. *Conclusions The observed diversity in root system growth and architecture occurs independently of semi-dwarf phenotypes, and is probably linked to a genetic background effect. The results show that there are no clear advantages of semi-dwarfism at low water availability in arabidopsis. [ABSTRACT FROM AUTHOR]

Abstract: Background: The diterpene cyclase ent-copalyl diphosphate synthase (CPS) catalyzes the first committed step in the biosynthesis of gibberellins. The previously reported 2.25Å resolution crystal structure of CPS complexed with (S)-15-aza-14,15-dihydrogeranylgeranyl thiolodiphosphate (1) established the αβγ domain architecture, but ambiguities regarding substrate analog binding remained. Method: Use of crystallization additives yielded CPS crystals diffracting to 1.55Å resolution. Additionally, active site residues that hydrogen bond with D379, either directly or through hydrogen bonded water molecules, were probed by mutagenesis. Results: This work clarifies structure–function relationships that were ambiguous in the lower resolution structure. Well-defined positions for the diphosphate group and tertiary ammonium cation of 1, as well as extensive solvent structure, are observed. Conclusions: Two channels involving hydrogen bonded solvent and protein residues lead to the active site, forming hydrogen bonded “proton wires” that link general acid D379 with bulk solvent. These proton wires may facilitate proton transfer with the general acid during catalysis. Activity measurements made with mutant enzymes indicate that N425, which donates a hydrogen bond directly to D379, and T421, which hydrogen bonds with D379 through an intervening solvent molecule, help orient D379 for catalysis. Residues involved in hydrogen bonds with the proton wire, R340 and D503, are also important. Finally, conserved residue E211, which is located near the diphosphate group of 1, is proposed to be a ligand to Mg2+ required for optimal catalytic activity. General significance: This work establishes structure–function relationships for class II terpenoid cyclases. [Copyright &y& Elsevier]