GA Biosynthesis Genes Research Articles

Cytokinins and the CRE1 receptor influence endogenous gibberellin levels in Medicago truncatula

ABSTRACTGibberellins (GAs) and cytokinins (CKs) are hormones that play antagonistic roles in several developmental processes in plants. However, there has been little exploration of their reciprocal interactions. Recent work in Medicago truncatula has revealed that GA signalling can regulate CK levels and response in roots. Here, we examine the reciprocal interaction, by assessing how CKs and the CRE1 (Cytokinin Response 1) CK receptor may influence endogenous GA levels. Real-Time RT-PCR analyses revealed that the expression of key GA biosynthesis genes is regulated in response to a short-term CK treatment and requires the CRE1 receptor. Similarly, GA quantifications indicated that a short-term CK treatment decreases the GA1 pool in wild-type plants and that GA levels are increased in the cre1 mutant compared to the wild-type. These data suggest that the M. truncatula CRE1-dependent CK signaling pathway negatively regulates bioactive GA levels.

Chromatin-remodeling factor OsINO80 is involved in regulation of gibberellin biosynthesis and is crucial for rice plant growth and development.

The phytohormone gibberellin (GA) plays essential roles in plant growth and development. Here, we report that OsINO80, a conserved ATP-dependent chromatin-remodeling factor in rice (Oryza sativa), functions in both GA biosynthesis and diverse biological processes. OsINO80-knockdown mutants, derived from either T-DNA insertion or RNA interference, display typical GA-deficient phenotypes, including dwarfism, reduced cell length, late flowering, retarded seed germination and impaired reproductive development. Consistently, transcriptome analyses reveal that OsINO80 knockdown results in downregulation by more than two-fold of over 1,000 genes, including the GA biosynthesis genes CPS1 and GA3ox2, and the dwarf phenotype of OsINO80-knockdown mutants can be rescued by the application of exogenous GA3. Chromatin immunoprecipitation (ChIP) experiments show that OsINO80 directly binds to the chromatin of CPS1 and GA3ox2 loci. Biochemical assays establish that OsINO80 specially interacts with histone variant H2A.Z and the H2A.Z enrichments at CPS1 and GA3ox2 are decreased in OsINO80-knockdown mutants. Thus, our study identified a rice chromatin-remodeling factor, OsINO80, and demonstrated that OsINO80 is involved in regulation of the GA biosynthesis pathway and plays critical functions for many aspects of rice plant growth and development.

The early inflorescence of Arabidopsis thaliana demonstrates positional effects in floral organ growth and meristem patterning

Key messageLinear modelling approaches detected significant gradients in organ growth and patterning across early flowers of the Arabidopsis inflorescence and uncovered evidence of new roles for gibberellin in floral development.Most flowering plants, including the genetic model Arabidopsis thaliana, produce multiple flowers in sequence from a reproductive shoot apex to form a flower spike (inflorescence). The development of individual flowers on an Arabidopsis inflorescence has typically been considered as highly stereotypical and uniform, but this assumption is contradicted by the existence of mutants with phenotypes visible in early flowers only. This phenomenon is demonstrated by mutants partially impaired in the biosynthesis of the phytohormone gibberellin (GA), in which floral organ growth is retarded in the first flowers to be produced but has recovered spontaneously by the 10th flower. We presently lack systematic data from multiple flowers across the Arabidopsis inflorescence to explain such changes. Using mutants of the GA 20-OXIDASE (GA20ox) GA biosynthesis gene family to manipulate endogenous GA levels, we investigated the dynamics of changing floral organ growth across the early Arabidopsis inflorescence (flowers 1–10). Modelling of floral organ lengths identified a significant, GA-independent gradient of increasing stamen length relative to the pistil in the wild-type inflorescence that was separable from other, GA-dependent effects. It was also found that the first flowers exhibited unstable organ patterning in contrast to later flowers and that this instability was prolonged by exogenous GA treatment. These findings indicate that the development of individual flowers is influenced by hitherto unknown factors acting across the inflorescence and also suggest novel functions for GA in floral patterning.

APETALA 2-domain-containing transcription factors: focusing on abscisic acid and gibberellins antagonism.

The phytohormones abscisic acid (ABA) and gibberellin (GA) antagonistically mediate diverse plant developmental processes including seed dormancy and germination, root development, and flowering time control, and thus the optimal balance between ABA and GA is essential for plant growth and development. Although more than a half and one century have passed since the initial discoveries of ABA and GA, respectively, the precise mechanisms underlying ABA-GA antagonism still need further investigation. Emerging evidence indicates that two APETALA 2 (AP2)-domain-containing transcription factors (ATFs), ABI4 in Arabidopsis and OsAP2-39 in rice, play key roles in ABA and GA antagonism. These two transcription factors precisely regulate the transcription pattern of ABA and GA biosynthesis or inactivation genes, mediating ABA and GA levels. In this Viewpoint article, we try to shed light on the effects of ATFs on ABA-GA antagonism, and summarize the overlapping but distinct biological functions of these ATFs in the antagonism between ABA and GA. Finally, we strongly propose that further research is needed into the detailed roles of additional numerous ATFs in ABA and GA crosstalk, which will improve our understanding of the antagonism between these two phytohormones.

Further insight into the role of KAN1, a member of KANADI transcription factor family in rice

The rice EMS-derived mutant leaf adaxialized 1 (lad1) was isolated based on its upward rolling leaf phenotype. Besides the adaxially rolled leaf, many other agronomic traits were also compromised in lad1. The rolling trait was characterized by a noticeable alteration of bulliform cells in the adaxial side of the leaves. Map-based cloning showed a single nucleotide substitution in the promoter region of the KAN1 gene in lad1 mutant. Further, over-expressing and CRISPR/cas9-edited knockdown transgenic plants confirmed that KAN1 was responsible for the mutant phenotype of lad1. Yeast two-hybrid and bimolecular fluorescence complementation assay demonstrated that KAN1 can interact with the auxin response factors ARF3, ARF7 and ARF15. Physiologically, the contents of auxin (IAA), abscisic acid (ABA), jasmonic acid (JA) and gibberellin (GA) were all significantly increased in the lad1 mutant. Moreover, the GA3 content dramatically decrease in wild-type, but increased in lad1 under IAA induction. Additionally, the expression levels of several IAA and GA biosynthesis and responsive-related genes and genes involved in leaf polarity determination were altered in lad1. Therefore, we hypothesized that KAN1/ARFs protein complexes act as auxin-dependent regulatory units that play a conserved role in leaf development.

Comparative transcriptome analysis of axillary buds in response to the shoot branching regulators gibberellin A3 and 6-benzyladenine in Jatropha curcas

Cytokinin (CK) is the primary hormone that positively regulates axillary bud outgrowth. However, in many woody plants, such as Jatropha curcas, gibberellin (GA) also promotes shoot branching. The molecular mechanisms underlying GA and CK interaction in the regulation of bud outgrowth in Jatropha remain unclear. To determine how young axillary buds respond to GA3 and 6-benzyladenine (BA), we performed a comparative transcriptome analysis of the young axillary buds of Jatropha seedlings treated with GA3 or BA. Two hundred and fifty genes were identified to be co-regulated in response to GA3 or BA. Seven NAC family members were down-regulated after treatment with both GA3 and BA, whereas these genes were up-regulated after treatment with the shoot branching inhibitor strigolactone. The expressions of the cell cycle genes CDC6, CDC45 and GRF5 were up-regulated after treatment with both GA3 and BA, suggesting they may promote bud outgrowth via regulation of the cell cycle machinery. In the axillary buds, BA significantly increased the expression of GA biosynthesis genes JcGA20oxs and JcGA3ox1, and down-regulated the expression of GA degradation genes JcGA2oxs. Overall, the comprehensive transcriptome data set provides novel insight into the responses of young axillary buds to GA and CK.

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.

Linking hydrogen-enhanced rice aluminum tolerance with the reestablishment of GA/ABA balance and miRNA-modulated gene expression: A case study on germination

Although previous results showed that exogenous hydrogen (H2) alleviated aluminum (Al) toxicity, the detailed mechanism remains unclear. Here, we reported that the exposure of germinating rice seeds to Al triggered H2 production, followed by a decrease of GA/ABA ratio and seed germination inhibition. Compared to inert gas (argon), H2 pretreatment not only strengthened H2 production and alleviated Al-induced germination inhibition, but also partially reestablished the balance between GA and ABA. By contrast, a GA biosynthesis inhibitor paclobutrazol (PAC) could block the H2-alleviated germination inhibition. The expression of GA biosynthesis genes (GA20ox1 and GA20ox2) and ABA catabolism genes (ABA8ox1 and ABA8ox2), was also induced by H2. Above results indicated that GA/ABA might be partially involved in H2 responses. Subsequent results revealed that compared with Al alone, transcripts of miR398a and miR159a were decreased by H2, and expression levels of their target genes OsSOD2 and OsGAMYB were up-regulated. Whereas, miR528 and miR160a transcripts were increased differentially, and contrasting tendencies were observed in the changes of their target genes (OsAO and OsARF10). The transcripts of Al-tolerant gene OsSTAR1/OsSTAR2 and OsFRDL4 were up-regulated. Above results were consistent with the anti-oxidant defense, decreased Al accumulation, and enhanced citrate efflux. Together, our results provided insight into the mechanism underlying H2-triggered Al tolerance in plants.

Regulation of ethylene-related gene expression by indole-3-acetic acid and 4-chloroindole-3-acetic acid in relation to pea fruit and seed development.

In pea, the auxins 4-chloroindole-3-acetic acid (4-Cl-IAA) and indole-3-acetic acid (IAA) occur naturally; however, only 4-Cl-IAA stimulates pericarp growth and gibberellin (GA) biosynthesis, and inhibits the ethylene response in deseeded ovaries (pericarps), mimicking the presence of seeds. Expression of ovary ethylene biosynthesis genes was regulated similarly in most cases by the presence of 4-Cl-IAA or seeds. PsACS1 [which encodes an enzyme that synthesizes 1-aminocyclopropane-1-carboxylic acid (ACC)] transcript abundance was high in pericarp tissue adjacent to developing seeds following pollination. ACC accumulation in 4-Cl-IAA-treated deseeded pericarps was driven by high PsASC1 expression (1800-fold). 4-Cl-IAA, but not IAA, also suppressed the pericarp transcript levels of PsACS4. 4-Cl-IAA increased PsACO1 and decreased PsACO2 and PsACO3 expression (enzymes that convert ACC to ethylene) but did not change ACO enzyme activity. Increased ethylene was countered by a 4-Cl-IAA-specific decrease in ethylene responsiveness potentially via modulation of pericarp ethylene receptor and signaling gene expression. This pattern did not occur in IAA-treated pericarps. Overall, the effect of 4-Cl-IAA and IAA on ethylene biosynthesis gene expression generally explains the ethylene evolution patterns, and their effects on GA biosynthesis and ethylene signaling gene expression explain the tissue response patterns in young pea ovaries.

Reactive oxygen species induced by heat stress during grain filling of rice (Oryza sativa L.) are involved in occurrence of grain chalkiness

Heat stress during grain filling increases rice grain chalkiness due to increased activity of α-amylase, which hydrolyzes starch. In rice and barley seeds, reactive oxygen species (ROS) produced after imbibition induce α-amylase activity via regulation of gibberellin (GA) and abscisic acid (ABA) levels during seed germination. Here, we examined whether ROS is involved in induction of grain chalkiness by α-amylase in developing rice grains under heat stress. To elucidate the role of ROS in grain chalkiness, we grew post-anthesis rice plants (Oryza sativa L. cv. Koshihikari) under control (25°C) or heat stress (30°C) conditions with or without antioxidant (dithiothreitol) treatment. The developing grains were analyzed for expression of NADPH oxidases, GA biosynthesis genes (OsGA3ox1, OsGA20ox1), ABA catabolism genes (OsABA8′OH1, OsABA8′OH2) and an α-amylase gene (OsAmy3E), endogenous H2O2 content and the grain quality. In grains exposed to heat stress, the expression of NADPH oxidase genes (especially, OsRbohB, OsRbohD, OsRbohF and OsRbohI) and the ROS content increased. Heat stress also increased the expression of OsGA3ox1, OsGA20ox1, OsABA8′OH1, OsABA8′OH2 and OsAmy3E. On the other hand, dithiothreitol treatment reduced the effects of heat stress on the expression of these genes and significantly reduced grain chalkiness induced by heat stress. These results suggest that, similar to cereal seed germination mechanism, ROS produced under heat stress is involved in α-amylase induction in maturating rice grains through GA/ABA metabolism, and consequently caused grain chalkiness.

GA as a regulatory link between the showy floral traits color and scent

Emission of volatiles at advanced stages of flower development is a strategy used by plants to lure pollinators to the flower. We reveal that GA negatively regulates floral scent production in petunia. We used Agrobacterium-mediated transient expression of GA-20ox in petunia flowers and a virus-induced gene silencing approach to knock down DELLA expression, measured volatile emission, internal pool sizes and GA levels by GC-MS or LC-MS/MS, and analyzed transcript levels of scent-related phenylpropanoid-pathway genes. We show that GA has a negative effect on the concentrations of accumulated and emitted phenylpropanoid volatiles in petunia flowers; this effect is exerted through transcriptional/post-transcriptional downregulation of regulatory and biosynthetic scent-related genes. Both overexpression of GA20-ox, a GA-biosynthesis gene, and suppression of DELLA, a repressor of GA-signal transduction, corroborated GA's negative regulation of floral scent. We present a model in which GA-dependent timing of the sequential activation of different branches of the phenylpropanoid pathway during flower development may represent a link between the showy traits controlling pollinator attraction, namely color and scent.

Altered gibberellin content affects growth and development in transgenic tobacco lines overexpressing a wheat gene encoding F-box protein

In a previous study, we have identified and characterized gene from wheat (Triticum aestivum L.) encoding F-box protein and named it TaFBA. In this paper, transgenic tobacco (Nicotiana tabacum L.) plants overexpressing TaFBA1 displayed accelerated growth early, but the rate slowed gradually at later stages of growth, and the mature transgenic plants were even shorter in stature and flowered later than did the wild type (WT). Treatment with gibberellin (GA) conferred an accelerated growth rate to the transgenic tobacco plants at later stages, similar to that of WT, whereas growth was inhibited more seriously in WT than in transgenic tobacco when plants were treated with a GA biosynthesis inhibitor. The content of GA in transgenic tobacco plants was higher at early developmental stages, but it was lower at later growth stages than in WT. Some GA biosynthesis genes were down regulated, which was accompanied with elevated expression of a GA catabolism gene. Thus, our results suggest that TaFBA1 is possibly involved in the regulation of plant growth and development, and that it may be related to the production, metabolism, and proper function of GA.

Soaking in H2O2 regulates ABA biosynthesis and GA catabolism in germinating cotton seeds under salt stress

Exogenous H2O2 improves seed germination with the involvement of ABA and GA in a number of plant species but how it affects cotton seed germination under salinity stress is not well documented. In this study, we found that the marked inhibition of cotton seed germination under salinity stress was considerably alleviated by pretreatment with H2O2. Salt stress increased the ABA content by upregulating ABA biosynthesis genes, NCED2, NCED5 and NCED9 and downregulating the ABA catabolism gene, CYP707A2. It also decreased the GA content by increasing the expression of GA catabolism gene, GA2ox1 and decreasing that of the GA biosynthesis gene, GA20ox1 during germination. Pretreatment with H2O2 downregulated the ABA biosynthesis genes, NCED5 and NCED9, thereby decreasing the ABA content in germinating seeds. Concurrently, it increased the GA content by downregulating the GA catabolism gene, GA2ox1. These results suggest that pretreatment with H2O2 improved cotton seed germination by mediating the downregulation of ABA catabolism and GA biosynthesis under salt stress.

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.

The QTL GNP1 Encodes GA20ox1, Which Increases Grain Number and Yield by Increasing Cytokinin Activity in Rice Panicle Meristems.

Cytokinins and gibberellins (GAs) play antagonistic roles in regulating reproductive meristem activity. Cytokinins have positive effects on meristem activity and maintenance. During inflorescence meristem development, cytokinin biosynthesis is activated via a KNOX-mediated pathway. Increased cytokinin activity leads to higher grain number, whereas GAs negatively affect meristem activity. The GA biosynthesis genes GA20oxs are negatively regulated by KNOX proteins. KNOX proteins function as modulators, balancing cytokinin and GA activity in the meristem. However, little is known about the crosstalk among cytokinin and GA regulators together with KNOX proteins and how KNOX-mediated dynamic balancing of hormonal activity functions. Through map-based cloning of QTLs, we cloned a GA biosynthesis gene, Grain Number per Panicle1 (GNP1), which encodes rice GA20ox1. The grain number and yield of NIL-GNP1TQ were significantly higher than those of isogenic control (Lemont). Sequence variations in its promoter region increased the levels of GNP1 transcripts, which were enriched in the apical regions of inflorescence meristems in NIL-GNP1TQ. We propose that cytokinin activity increased due to a KNOX-mediated transcriptional feedback loop resulting from the higher GNP1 transcript levels, in turn leading to increased expression of the GA catabolism genes GA2oxs and reduced GA1 and GA3 accumulation. This rebalancing process increased cytokinin activity, thereby increasing grain number and grain yield in rice. These findings uncover important, novel roles of GAs in rice florescence meristem development and provide new insights into the crosstalk between cytokinin and GA underlying development process.

The ERF11 Transcription Factor Promotes Internode Elongation by Activating Gibberellin Biosynthesis and Signaling.

The phytohormone gibberellin (GA) plays a key role in promoting stem elongation in plants. Previous studies show that GA activates its signaling pathway by inducing rapid degradation of DELLA proteins, GA signaling repressors. Using an activation-tagging screen in a reduced-GA mutant ga1-6 background, we identified AtERF11 to be a novel positive regulator of both GA biosynthesis and GA signaling for internode elongation. Overexpression of AtERF11 partially rescued the dwarf phenotype of ga1-6 AtERF11 is a member of the ERF (ETHYLENE RESPONSE FACTOR) subfamily VIII-B-1a of ERF/AP2 transcription factors in Arabidopsis (Arabidopsis thaliana). Overexpression of AtERF11 resulted in elevated bioactive GA levels by up-regulating expression of GA3ox1 and GA20ox genes. Hypocotyl elongation assays further showed that overexpression of AtERF11 conferred elevated GA response, whereas loss-of-function erf11 and erf11 erf4 mutants displayed reduced GA response. In addition, yeast two-hybrid, coimmunoprecipitation, and transient expression assays showed that AtERF11 enhances GA signaling by antagonizing the function of DELLA proteins via direct protein-protein interaction. Interestingly, AtERF11 overexpression also caused a reduction in the levels of another phytohormone ethylene in the growing stem, consistent with recent finding showing that AtERF11 represses transcription of ethylene biosynthesis ACS genes. The effect of AtERF11 on promoting GA biosynthesis gene expression is likely via its repressive function on ethylene biosynthesis. These results suggest that AtERF11 plays a dual role in promoting internode elongation by inhibiting ethylene biosynthesis and activating GA biosynthesis and signaling pathways.

Genome-wide identification and expression profiling reveal tissue-specific expression and differentially-regulated genes involved in gibberellin metabolism between Williams banana and its dwarf mutant.

BackgroundDwarfism is one of the most valuable traits in banana breeding because semi-dwarf cultivars show good resistance to damage by wind and rain. Moreover, these cultivars present advantages of convenient cultivation, management, and so on. We obtained a dwarf mutant ‘8818-1’ through EMS (ethyl methane sulphonate) mutagenesis of Williams banana 8818 (Musa spp. AAA group). Our research have shown that gibberellins (GAs) content in 8818-1 false stems was significantly lower than that in its parent 8818 and the dwarf type of 8818-1 could be restored by application of exogenous GA3. Although GA exerts important impacts on the 8818-1 dwarf type, our understanding of the regulation of GA metabolism during banana dwarf mutant development remains limited.ResultsGenome-wide screening revealed 36 candidate GA metabolism genes were systematically identified for the first time; these genes included 3 MaCPS, 2 MaKS, 1 MaKO, 2 MaKAO, 10 MaGA20ox, 4 MaGA3ox, and 14 MaGA2ox genes. Phylogenetic tree and conserved protein domain analyses showed sequence conservation and divergence. GA metabolism genes exhibited tissue-specific expression patterns. Early GA biosynthesis genes were constitutively expressed but presented differential regulation in different tissues in Williams banana. GA oxidase family genes were mainly transcribed in young fruits, thus suggesting that young fruits were the most active tissue involved in GA metabolism, followed by leaves, bracts, and finally approximately mature fruits. Expression patterns between 8818 and 8818-1 revealed that MaGA20ox4, MaGA20ox5, and MaGA20ox7 of the MaGA20ox gene family and MaGA2ox7, MaGA2ox12, and MaGA2ox14 of the MaGA2ox gene family exhibited significant differential expression and high-expression levels in false stems. These genes are likely to be responsible for the regulation of GAs content in 8818-1 false stems.ConclusionOverall, phylogenetic evolution, tissue specificity and differential expression analyses of GA metabolism genes can provide a better understanding of GA-regulated development in banana. The present results revealed that MaGA20ox4, MaGA20ox5, MaGA20ox7, MaGA2ox7, MaGA2ox12, and MaGA2ox14 were the main genes regulating GA content difference between 8818 and 8818-1. All of these genes may perform important functions in the developmental processes of banana, but each gene may perform different functions in different tissues or during different developmental stages.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-016-0809-1) contains supplementary material, which is available to authorized users.

Auxin- and cytokinin-induced berries set in grapevine partly rely on enhanced gibberellin biosynthesis

Gibberellins (GAs) have been widely used for many years to induce seedless grapevine and increase fruit set in production. However, the role of GAs and how they crosstalk with auxin and cytokinin during fruit set in grapevine remains unclarified. To investigate their role, GA3, 4-chlorophenoxyacetic acid (4-CPA), 6-benzylaminopurine (6-BA), and different hormone combinations were applied to unpollinated ovaries of the ‘Fenghou’ grape (Vitis vinifera × Vitis labrusca) at anthesis. The results showed that the application of 4-CPA, 6-BA, GA3, 4-CPA+GA3, 6-BA+GA3, and 4-CPA+6-BA induced parthenocarpy. Among them, 4-CPA-, 6-BA-, and 4-CPA+6-BA-induced fruits were smaller than those induced by GA3, 4-CPA+GA3, and 6-BA+GA3. Application of the GA biosynthesis inhibitor paclobutrazol reduced both the fresh weight and fruit set of 4-CPA- and 6-BA-induced fruits, but the effect of the inhibitor was reversed by the application of GA3. In contrast to unpollinated ovaries, the ovaries induced by 4-CPA and 6-BA showed enhanced accumulation of active GAs, but at a lower level than in pollinated ovaries between 7 and 21 days after anthesis (DAA). Gene analysis showed that the increase in the GA content in 4-CPA- and 6-BA-treated ovaries was the result of the upregulation of GA biosynthesis genes, such as VvGA3ox1, and suppression of GA catabolism genes, such as VvGA2ox3 and VvGA2ox4. In addition, the concentration of active IAA was enhanced in the ovaries induced by 6-BA, which was accompanied by the elevated expression of the IAA biosynthesis genes VvYUC2 and VvYUC6. These results suggested that 4-CPA- and 6-BA-induced fruit set in grapevine requires downstream gibberellin biosynthesis.

Regulatory Networks in Pollen Development under Cold Stress.

Cold stress modifies anthers’ metabolic pathways to induce pollen sterility. Cold-tolerant plants, unlike the susceptible ones, produce high proportion of viable pollen. Anthers in susceptible plants, when exposed to cold stress, increase abscisic acid (ABA) metabolism and reduce ABA catabolism. Increased ABA negatively regulates expression of tapetum cell wall bound invertase and monosaccharide transport genes resulting in distorted carbohydrate pool in anther. Cold-stress also reduces endogenous levels of the bioactive gibberellins (GAs), GA4 and GA7, in susceptible anthers by repression of the GA biosynthesis genes. Here, we discuss recent findings on mechanisms of cold susceptibility in anthers which determine pollen sterility. We also discuss differences in regulatory pathways between cold-stressed anthers of susceptible and tolerant plants that decide pollen sterility or viability.

Ectopic expression of a cytochrome P450 monooxygenase gene PtCYP714A3 from Populus trichocarpa reduces shoot growth and improves tolerance to salt stress in transgenic rice.

SummaryIn Arabidopsis thaliana and Oryza sativa, the cytochrome P450 (CYP) 714 protein family represents a unique group of CYP monooxygenase, which functions as a shoot‐specific regulator in plant development through gibberellin deactivation. Here, we report the functional characterizations of PtCYP714A3, an OsCYP714D1/Eui homologue from Populus trichocarpa. PtCYP714A3 was ubiquitously expressed with the highest transcript level in cambium–phloem tissues, and was greatly induced by salt and osmotic stress in poplar. Subcellular localization analyses indicated that PtCYP714A3‐YFP fusion protein was targeted to endoplasmic reticulum (ER). Expression of PtCYP714A3 in the rice eui mutant could rescue its excessive‐shoot‐growth phenotype. Ectopic expression of PtCYP714A3 in rice led to semi‐dwarfed phenotype with promoted tillering and reduced seed size. Transgenic lines which showed significant expression of PtCYP714A3 also accumulated lower GA level than did the wild‐type (WT) plants. The expression of some GA biosynthesis genes was significantly suppressed in these transgenic plants. Furthermore, transgenic rice plants exhibited enhanced tolerance to salt and maintained more Na+ in both shoot and root tissues under salinity stress. All these results not only suggest a crucial role of PtCYP714A3 in shoot responses to salt toxicity in rice, but also provide a molecular basis for genetic engineering of salt‐tolerant crops.