BBX24 Interacts with JAZ3 to Promote Growth by Reducing DELLA Activity in Shade Avoidance

Shade avoidance syndrome (SAS) is a strategy of major adaptive significance and typically includes elongation of the stem and petiole, leaf hyponasty, reduced branching and phototropic orientation of the plant shoot toward canopy gaps. Both cryptochrome 1 and phytochrome B (phyB) are the major photoreceptors that sense the reduction in the blue light fluence rate and the low red:far-red ratio, respectively, and both light signals are associated with plant density and the resource reallocation when SAS responses are triggered. The B-box (BBX)-containing zinc finger transcription factor BBX24 has been implicated in the SAS as a regulator of DELLA activity, but this interaction does not explain all the observed BBX24-dependent regulation in shade light. Here, through a combination of transcriptional meta-analysis and large-scale identification of BBX24-interacting transcription factors, we found that JAZ3, a jasmonic acid signaling component, is a direct target of BBX24. Furthermore, we demonstrated that joint loss of BBX24 and JAZ3 function causes insensitivity to DELLA accumulation, and the defective shade-induced elongation in this mutant is rescued by loss of DELLA or phyB function. Therefore, we propose that JAZ3 is part of the regulatory network that controls the plant growth in response to shade, through a mechanism in which BBX24 and JAZ3 jointly regulate DELLA activity. Our results provide new insights into the participation of BBX24 and JA signaling in the hypocotyl shade avoidance response in Arabidopsis.

Auxins of microbial origin and their use in agriculture

To maintain the world population demand, a sustainable agriculture is needed. Since current global vision is more friendly with the environment, eco-friendly alternatives are desirable. In this sense, plant growth-promoting rhizobacteria could be the choice for the management of soil-borne diseases of crop plants. These rhizobacteria secrete chemical compounds which act as phytohormones. Indole-3-acetic acid (IAA) is the most common plant hormone of the auxin class which regulates various processes of plant growth. IAA compound, in which structure can be found a carboxylic acid attached through a methylene group to the C-3 position of an indole ring, is produced both by plants and microorganisms. Plant growth-promoting rhizobacteria and fungi secrete IAA to promote the plant growth. In this review, IAA production and mechanisms of action by bacteria and fungi along with the metabolic pathways evolved in the IAA secretion and commercial prospects are revised.Key points• Many microorganisms produce auxins which help the plant growth promotion.• These auxins improve the plant growth by several mechanisms.• The auxins are produced through different mechanisms.

Bioactivity of essential oils in phytopathogenic and post-harvest fungi control

Commercial thyme and lavender essential oils were analysed by GC/MS. Sixty-six compounds accounting for 98.6-99.6% of total essential oil were identified. Thymol (52.14 ± 0.21%), followed by p-cymene (32.24 ± 0.16%), carvacrol (3.71 ± 0.01%) and γ-terpinene (3.34 ± 0.02%), were the main compounds in thyme essential oil, while large amounts of oxygenated monoterpenes linalool acetate (37.07 ± 0.24%) and linalool (30.16 ± 0.06%) were found in lavender one. In vitro antifungal activity of the essential oils was evaluated at 200 and 300 μg/mL against 10 phytopathogenic and post-harvest fungi, which significantly affect agriculture. Micelial growth inhibition was calculated for each tested fungus and dose. Thyme essential oil showed satisfactory results with 90-100% growth inhibition in almost all the assayed fungi at 300 μg/mL, while lavender essential oil showed no noteworthy inhibition data at either dose, and its growth was even enhanced. Thyme essential oil represents a natural alternative to control harvest and post-harvest fungi, and to extend the shelf-life of agriculture products.

Perturbation of spermine synthase gene expression and transcript profiling provide new insights on the role of the tetraamine spermine in Arabidopsis defense against Pseudomonas viridiflava

The role of the tetraamine spermine in plant defense against pathogens was investigated by using the Arabidopsis (Arabidopsis thaliana)-Pseudomonas viridiflava pathosystem. The effects of perturbations of plant spermine levels on susceptibility to bacterial infection were evaluated in transgenic plants (35S::spermine synthase [SPMS]) that overexpressed the SPMS gene and accumulated spermine, as well as in spms mutants with low spermine levels. The former exhibited higher resistance to P. viridiflava than wild-type plants, while the latter were more susceptible. Exogenous supply of spermine to wild-type plants also increased disease resistance. Increased resistance provided by spermine was partly counteracted by the polyamine oxidase inhibitor SL-11061, demonstrating that the protective effect of spermine partly depends on its oxidation. In addition, global changes in gene expression resulting from perturbations of spermine levels were analyzed by transcript profiling 35S::SPMS-9 and spms-2 plants. Overexpression of 602 genes was detected in 35S::SPMS-9 plants, while 312 genes were down-regulated, as compared to the wild type. In the spms-2 line, 211 and 158 genes were up- and down-regulated, respectively. Analysis of gene ontology term enrichment demonstrated that many genes overexpressed only in 35S::SPMS-9 participate in pathogen perception and defense responses. Notably, several families of disease resistance genes, transcription factors, kinases, and nucleotide- and DNA/RNA-binding proteins were overexpressed in this line. Thus, a number of spermine-responsive genes potentially involved in resistance to P. viridiflava were identified. The obtained results support the idea that spermine contributes to plant resistance to P. viridiflava.

Tetrandrine and Isotetrandrine, Two Bisbenzyltetrahydroisoquinoline Alkaloids from Menispermaceae, with Rat Uterine Smooth Muscle Relaxant Activity

The effects of two bisbenzyltetrahydroisoquinoline alkaloids, 1S, 1′S tetrandrine and its isomer 1R, 1′S isotetrandrine, were investigated in rat isolated uterus in order to identify the mechanism of relaxant action and to study the influence of the absolute configuration on the activity of these alkaloids. Both inhibited the uterine contraction induced by high K+, acetylcholine and oxytocin. In Ca2+-free medium, isotetrandrine relaxed the sustained contraction induced by oxytocin but tetrandrine did not. The relaxant effects of the alkaloids may be due to blockade of calcium influx through specific channels. Tetrandrine and isotetrandrine modify the calcium channel in a nonreversible manner whilst only isotetrandrine acts intracellularly. Tetrandrine shows a more specific relaxant activity as a calcium entry blocker.

A molecular framework for light and gibberellin control of cell elongation

Cell elongation during seedling development is antagonistically regulated by light and gibberellins (GAs). Light induces photomorphogenesis, leading to inhibition of hypocotyl growth, whereas GAs promote etiolated growth, characterized by increased hypocotyl elongation. The mechanism underlying this antagonistic interaction remains unclear. Here we report on the central role of the Arabidopsis thaliana nuclear transcription factor PIF4 (encoded by PHYTOCHROME INTERACTING FACTOR 4) in the positive control of genes mediating cell elongation and show that this factor is negatively regulated by the light photoreceptor phyB (ref. 4) and by DELLA proteins that have a key repressor function in GA signalling. Our results demonstrate that PIF4 is destabilized by phyB in the light and that DELLAs block PIF4 transcriptional activity by binding the DNA-recognition domain of this factor. We show that GAs abrogate such repression by promoting DELLA destabilization, and therefore cause a concomitant accumulation of free PIF4 in the nucleus. Consistent with this model, intermediate hypocotyl lengths were observed in transgenic plants over-accumulating both DELLAs and PIF4. Destabilization of this factor by phyB, together with its inactivation by DELLAs, constitutes a protein interaction framework that explains how plants integrate both light and GA signals to optimize growth and development in response to changing environments.

Chemical variations in the essential oil of Sideritis tragoriganum

The essential oil composition from Sideritis tragoriganum has been investigated by capillary gas chromatography and gas chromatography-mass spectrometry. Among the 47 identified mono- and sesquiterpenes, alpha-bisabolol is the most prominent component. Correlation analysis of essential oil components from this population of S. tragoriganum with two other geographically distinct populations revealed the existence of unrelated chemical types.

Chemotaxonomic value of the essential oil compounds in species of Teucrium pumilum aggregate

Volatile compounds from the aerial parts of Teucrium lepicephalum Pau and Teucrium carolipaui C. Vicioso ex Pau, both belonging to the Teucrium pumilum aggregate, were analysed by capillary GC and GC-MS. From the common and specific compounds (mono- and sesquiterpenes) of the two taxa, chemical characterization was carried out and taxonomic relationships were assessed. Application of the cluster and k-means discriminant analysis shows a differential chemical relationship between T. lepicephalum and Teucrium carolipaui.

Integration of floral inductive signals in Arabidopsis

Flowering of Arabidopsis is regulated by a daylength-dependent pathway that accelerates flowering in long days and a daylength-independent pathway that ensures flowering in the absence of inductive conditions. These pathways are genetically separable, as there are mutations that delay flowering in long but not short days. Conversely, mutations that block synthesis of the hormone gibberellin abolish flowering in short days, but have on their own only a minor effect in long days. A third pathway, the autonomous pathway, probably acts by modulating the other two pathways. Understanding where and how these pathways are integrated is a prerequisite for understanding why similar environmental or endogenous cues can elicit opposite flowering responses in different plants. In Arabidopsis, floral induction leads ultimately to the upregulation of floral meristem-identity genes such as LEAFY, indicating that floral inductive signals are integrated upstream of LEAFY Here we show that gibberellins activate the LEAFY promoter through cis elements that are different from those that are sufficient for the daylength response, demonstrating that the LEAFY promoter integrates environmental and endogenous signals controlling flowering time.

Activation tagging in Arabidopsis

Activation tagging using T-DNA vectors that contain multimerized transcriptional enhancers from the cauliflower mosaic virus (CaMV) 35S gene has been applied to Arabidopsis plants. New activation-tagging vectors that confer resistance to the antibiotic kanamycin or the herbicide glufosinate have been used to generate several tens of thousands of transformed plants. From these, over 30 dominant mutants with various phenotypes have been isolated. Analysis of a subset of mutants has shown that overexpressed genes are almost always found immediately adjacent to the inserted CaMV 35S enhancers, at distances ranging from 380 bp to 3.6 kb. In at least one case, the CaMV 35S enhancers led primarily to an enhancement of the endogenous expression pattern rather than to constitutive ectopic expression, suggesting that the CaMV 35S enhancers used here act differently than the complete CaMV 35S promoter. This has important implications for the spectrum of genes that will be discovered by this method.

Chiral discrimination of the analgesic cizolirtine by using cyclodextrins: A (1)H NMR study on the solution structures of their host-guest complexes

The use of four cyclodextrins (three native and one beta-CD derivative) as NMR chiral solvating agents to resolve the enantiomers of (+/-)-cizolirtine, 1, and its chemical precursor (the carbinol, (+/-)-2), was investigated. The best enantiodiscrimination occurred when beta-cyclodextrin was used. ROESY experiments were performed to qualitatively ascertain the most probable host-guest structures in D(2)O solution, and the binding features found were explained in terms of spatial fitting of the guest molecules into the macrocyclic cavities. No geometrical differences were noted between the two diastereomeric complexes formed by a cyclodextrin and a racemic substrate, so the magnetic nonequivalence induced on guest protons by the enantioselective binding had to be explained as a result of subtle disparities in the orientation and/or the conformational state of the complexed enantiomers.

Independent regulation of flowering by phytochrome B and gibberellins in Arabidopsis

Phytochromes and gibberellins (GAs) coordinately regulate multiple aspects of Arabidopsis development. Phytochrome B (PHYB) promotes seed germination by increasing GA biosynthesis, but inhibits hypocotyl elongation by decreasing the responsiveness to GAs. Later in the life cycle of the plant, PHYB and GAs have opposite effects on flowering. PHYB delays flowering, while GAs promote flowering, particularly under noninductive photoperiods. To learn how PHYB and GAs interact in the control of flowering, we have analyzed the effect of a phyB mutation on flowering time and on the expression of the floral meristem-identity gene LFY (LEAFY). We show that the early flowering caused by phyB correlated with an increase in LFY expression, which complements our previous finding that GAs are required for activation of LFY under noninductive photoperiods (M.A. Blázquez, R. Green, O. Nilsson, M.R. Sussman, D. Weigel [1998] Plant Cell 10: 791-800). Since phyB did not change the GA responsiveness of the LFY promoter and suppressed the lack of flowering of severe GA-deficient mutants under short days, we propose that PHYB modulates flowering time at least partially through a GA-independent pathway. Interestingly, the effects of PHYB on flowering do not seem to be mediated by transcriptional up-regulation of genes such as CO (CONSTANS) and FT (Flowering locus T), which are known to mediate the effects of the photoperiod-dependent floral-induction pathway.

Flowering-time genes modulate the response to LEAFY activity

Among the genes that control the transition to flowering in Arabidopsis is a large group whose inactivation causes a delay in flowering. It has been difficult to establish different pathways in which the flowering-time genes might act, because mutants with lesions in these genes have very similar phenotypes. Among the putative targets of the flowering-time genes is another group of genes, which control the identity of individual meristems. Overexpression of one of the meristem-identity genes, LEAFY, can cause the precocious generation of flowers and thus early flowering. We have exploited the opposite phenotypes seen in late-flowering mutants and LEAFY overexpressers to clarify the genetic interactions between flowering-time genes and LEAFY. According to epistatic relationships, we can define one class of flowering-time genes that affects primarily the response to LEAFY activity, and another class of genes that affects primarily the transcriptional induction of LEAFY. These observations allow us to expand previously proposed models for the genetic control of flowering time.

Styryl-pyrones from Goniothalamus arvensis

Two novel styrl-pyrones, (+)-garvensintriol and (+)-etharvendiol, together with a known cytotoxic furano-furone, (+)-goniofufurone, have been isolated from the stem bark of Goniothalamus arvensis. A different relative configuration, cis-erythro-erythro for garvensintriol and cis-threo-erythro for etharvendiol, is established, and their absolute stereochemistry is discussed.

Isolation and molecular characterization of the Arabidopsis TPS1 gene, encoding trehalose-6-phosphate synthase

An Arabidopsis thaliana cDNA clone, AtTPS1, that encodes a trehalose-6-phosphate synthase was isolated. The identity of this protein is supported by both structural and functional evidence. On one hand, the predicted sequence of the protein encoded by AtTPS1 showed a high degree of similarity with trehalose-6-phosphate synthases of different organisms. On the other hand, expression of the AtTPS1 cDNA in the yeast tps1 mutant restored its ability to synthesize trehalose and suppressed its growth defect related to the lack of trehalose-6-phosphate. Genomic organization and expression analyses suggest that AtTPS1 is a single-copy gene and is expressed constitutively at very low levels.

LEAFY expression and flower initiation in Arabidopsis

During the initial vegetative phase, the Arabidopsis shoot meristem produces leaves with associated lateral shoots at its flanks, while the later reproductive phase is characterized by the formation of flowers. The LEAFY gene is an important element of the transition from the vegetative to the reproductive phase, as LEAFY is both necessary and sufficient for the initiation of individual flowers. We have analyzed in detail the expression of LEAFY during the plant life cycle, and found that LEAFY is extensively expressed during the vegetative phase. In long days, Arabidopsis plants flower soon after germination, and this is paralleled by rapid upregulation of LEAFY. In short days, Arabidopsis plants flower several weeks later than in long days, but LEAFY expression increases gradually before flowering commences. Application of the plant hormone gibberellin, which hastens flowering in short days, enhances the gradual change in LEAFY expression observed in short days. Changes in LEAFY expression before the transition to flowering suggest that the time point of this transition is at least partly controlled by the levels of LEAFY activity that are prevalent at a given time of the life cycle. This assumption is borne out by the finding that increasing the copy number of endogenous LEAFY reduces the number of leaves produced before the first flower is formed. Thus, LEAFY combines properties of flowering-time and flower-meristem-identity genes, indicating that LEAFY is a direct link between the global process of floral induction and the regional events associated with the initiation of individual flowers.

Illuminating flowers: CONSTANS induces LEAFY expression

Higher plants must undergo a major developmental switch, the transition to flowering, if they are to successfully complete their life cycle. In many plants, the crucial decision of when to begin to produce flowers is primarily controlled by environmental signals. The process of floral induction involves the integration of the activities of two types of genes: those that control flowering time as a response to the environment as well as an endogenous clock, and those that determine the floral identity of the cells. The first direct link between these two classes of genes has now been demonstrated. Forced expression of CONSTANS, a flowering-time gene, promotes flowering through the transcriptional activation of LEAFY, a flower-meristem-identity gene.

Schizosaccharomyces pombe possesses an unusual and a conventional hexokinase: biochemical and molecular characterization of both hexokinases

Two hexokinases were characterized in Schizosaccharomyces pombe: hexokinase 1, with a low phosphorylation coefficient on glucose (Km 8.5 mM) and hexokinase 2, a kinetically conventional hexokinase. Genes hxk1+ and hxk2+ encoding these enzymes were cloned and sequenced. Disruption of hxk1+ had no effect on growth but disruption of hxk2+ doubled the generation time in glucose. Spores carrying the double disruption hxk1+ hxk2+ did not grow on glucose or fructose after one week. Expression of hxk1+ increased strongly during growth in fructose or glycerol. Expression of hxk2+ was highest during growth in glycerol. A NADP-dependent glucose dehydrogenase was detected, but not a glucokinase.

Mode of action of the qcr9 and cat3 mutations in restoring the ability of Saccharomyces cerevisiae tps1 mutants to grow on glucose

Mutations in the TPS1 gene, which encodes trehalose-6-P synthase, cause a glucose-negative phenotype in Saccharomyces cerevisiae. Antimycin A or disruption of the QCR9 gene, which encodes one subunit of the cytochrome bc1 complex, restore the ability to grow in glucose-containing media. Under these conditions the cell excreted a large amount of glycerol, corresponding to about 20% of the glucose taken up. Suppression appears to be achieved by diversion of accumulated glycolytic intermediates to the production of glycerol, thereby providing NAD+ and phosphate for the glyceraldehyde-3-P dehydrogenase reaction. Analysis of the mutation sci1-1, which also suppresses the glucose-negative phenotype of tps1 mutants, showed that glucose transport was decreased in sci1-1 mutants. The gene SCI1 was cloned and its nucleotide sequence revealed it to be identical to CAT3/SNF4. The suppression mediated by sci1-1 is attributable to a decrease in glycolytic flux.

A mutation affecting carbon catabolite repression suppresses growth defects in pyruvate carboxylase mutants from Saccharomyces cerevisiae

Yeasts with disruptions in the genes PYC1 and PYC2 encoding the isoenzymes of pyruvate carboxylase cannot grow in a glucose-ammonium medium (Stucka et al. (1991) Mol. Gen. Genet. 229, 307-315). We have isolated a dominant mutation, BPC1-1, that allows growth in this medium of yeasts with interrupted PYC1 and PYC2 genes. The BPC1-1 mutation abolishes catabolite repression of a series of genes and allows expression of the enzymes of the glyoxylate cycle during growth in glucose. A functional glyoxylate cycle is necessary for suppression as a disruption of gene ICL1 encoding isocitrate lyase abolished the phenotypic effect of BPC1-1 on growth in glucose-ammonium. Concurrent expression from constitutive promoters of genes ICL1 and MLS1 (encoding malate synthase) also suppressed the growth phenotype of pyc1 pyc2 mutants. The mutation BPC1-1 is either allelic or closely linked to the mutation DGT1-1.

Lack of lactate-proton symport activity in pck1 mutants of Saccharomyces cerevisiae

Mutants of Saccharomyces cerevisiae without phosphoenolpyruvate carboxykinase activity showed no measurable lactate proton symport, while mutants without fructose-1,6-bisphosphatase had normal transport activity. Incubation of a pck1 mutant, under derepression conditions in the presence of glycerol, restored the activity of the lactate-proton symport, with identical kinetic characteristics to that in the wild-type. For efficient lactate-proton symport activity, not only is an external inducer such as lactic acid needed, but also a molecule derived from the acid metabolism may be necessary.

Effects on rat uterine and aorta strip smooth muscle of Thymus leptophyllus extract

The diethylether extract from Thymus leptophyllus was found to be more active on uterine smooth muscle than on aorta strips. Rat uterus experiments with and without extracellular calcium, yielded similar IC50 values. A nonspecific mechanism for the relaxant activity can therefore be postulated. In rat aorta and in the presence of extracellular calcium the extract inhibited the contractile response induced by K+ depolarizing solution and had a less inhibitory effect on noradrenaline (NA) contraction. In a Ca(2+)-free solution the extract strongly reduced the Ca(2+)-release induced by NA, but it did not affect the transient contraction caused by caffeine (CAF).

Use of Yarrowia lipolytica hexokinase for the quantitative determination of trehalose 6-phosphate

This paper describes a procedure for the quantitative determination of trehalose 6-phosphate (T6P) based on its ability to inhibit hexokinase from Yarrowia lipolytica. The assay is linear between 1 nmol and at least 8 nmol. The concentration of T6P in wild-type Saccharomyces cerevisiae (0.15 mM) and in ras2 mutants (0.25 mM) remained unchanged in the exponential or stationary phase of growth or after heat shock. A tps1 mutant affected in T6P synthase did not show detectable T6P. Heat shock increased the concentration of T6P in Schizosaccharomyces pombe from 0.43 to 0.75 mM.

Trehalose-6-P synthase is dispensable for growth on glucose but not for spore germination in Schizosaccharomyces pombe

Trehalose-6-P inhibits hexokinases in Saccharomyces cerevisiae (M. A. Blázquez, R. Lagunas, C. Gancedo, and J. M. Gancedo, FEBS Lett. 329:51-54, 1993), and disruption of the TPS1 gene (formerly named CIF1 or FDP1) encoding trehalose-6-P synthase prevents growth in glucose. We have found that the hexokinase from Schizosaccharomyces pombe is not inhibited by trehalose-6-P even at a concentration of 3 mM. The highest internal concentration of trehalose-6-P that we measured in S. pombe was 0.75 mM after heat shock. We have isolated from S. pombe the tps1+ gene, which is homologous to the Saccharomyces cerevisiae TPS1 gene. The DNA sequence from tps1+ predicts a protein of 479 amino acids with 65% identity with the protein of S. cerevisiae. The tps1+ gene expressed from its own promoter could complement the lack of trehalose-6-P synthase in S. cerevisiae tps1 mutants. The TPS1 gene from S. cerevisiae could also restore trehalose synthesis in S. pombe tps1 mutants. A chromosomal disruption of the tps1+ gene in S. pombe did not have a noticeable effect on growth in glucose, in contrast with the disruption of TPS1 in S. cerevisiae. However, the disruption prevented germination of spores carrying it. The level of an RNA hybridizing with an internal probe of the tps1+ gene reached a maximum after 20 min of heat shock treatment. The results presented support the idea that trehalose-6-P plays a role in the control of glycolysis in S. cerevisiae but not in S. pombe and show that the trehalose pathway has different roles in the two yeast species.

Influence of the absolute configuration on the vascular effects of tetrandrine and isotetrandrine in rat aorta

The relaxant action of (1S, 1'S) tetrandrine and its isomer (1R, 1'S) isotetrandrine were examined in rat aortic strips, in presence or absence of extracellular calcium. Both alkaloids relax, concentration dependently, the contractile response elicited by depolarizing solution (KCl 80 mM) or noradrenaline (1 microM). Tetrandrine, however, showed a selectivity of action towards the KCl-induced contraction while isotetrandrine did not. In Ca(2+)-free solution, both alkaloids inhibited the contraction induced by noradrenaline, but they did not affect the transient contraction due to caffeine then this effect is not attributable to direct inhibition of the smooth muscle contractile elements. The refilling of intracellular calcium stores sensitive to noradrenaline or caffeine was significantly inhibited by both alkaloids.

Identification of extragenic suppressors of the cif1 mutation in Saccharomyces cerevisiae

The cif1 mutation of Saccharomyces cerevisiae causes inability to grow on glucose and related fermentable carbon sources. We have isolated two different suppressor mutations that allow growth on glucose of yeasts carrying the cif1 mutation. One of them, sci1-1, is recessive and caused inability to grow on non-fermentable carbon sources and to de-repress fructose-1,6-bisphosphatase. The other suppressor mutation, SCI2-1, is dominant and diminished the capacity to phosphorylate glucose or fructose. The SCI2-1 mutation decreased sporulation efficiency by 70% in heterozygosis and by more than 90% in homozygosis. In a CIF1 background, cells carrying the mutation SCI2-1 accumulated trehalose during the logarithmic phase of growth and hyperaccumulated it during the stationary phase. Genetic tests showed that SCI2 was either allelic, or else closely linked, to HXK2. The concentrations of the glycolytic metabolites measured during growth on glucose in cells carrying the cif1 mutation and any of the suppressor mutations were similar to those of a wild-type. Both types of suppressor mutations restored the transient cAMP response to glucose to cif1 mutants.

Trehalose-6-phosphate, a new regulator of yeast glycolysis that inhibits hexokinases

Trehalose-6-phosphate (P) competitively inhibited the hexokinases from Saccharomyces cerevisiae. The strongest inhibition was observed upon hexokinase II, with a Ki of 40 microM, while in the case of hexokinase I the Ki was 200 microM. Glucokinase was not inhibited by trehalose-6-P up to 5 mM. This inhibition appears to have physiological significance, since the intracellular levels of trehalose-6-P were about 0.2 mM. Hexokinases from other organisms were also inhibited, while glucokinases were unaffected. The hexokinase from the yeast, Yarrowia lipolytica, was particularly sensitive to the inhibition by trehalose-6-P: when assayed with 2 mM fructose an apparent Ki of 5 microM was calculated. Two S. cerevisiae mutants with abnormal levels of trehalose-6-P exhibited defects in glucose metabolism. It is concluded that trehalose-6-P plays an important role in the regulation of the first steps of yeast glycolysis, mainly through the inhibition of hexokinase II.

The fdp1 and cif1 mutations are caused by different single nucleotide changes in the yeast CIF1 gene

The allelism between the mutations cif1 and fdp1 from Saccharomyces cerevisiae has been demonstrated using PCR techniques and complementation of function. The cif1 mutation results in a shortened version of the protein while the fdp1 mutation introduces a charged residue in a highly hydrophobic stretch.

Molecular cloning of CIF1, a yeast gene necessary for growth on glucose

The cif1 mutation of Saccharomyces cerevisiae (Navon et al., Biochemistry 18, 4487-4499, 1979) causes inability to grow on glucose and absence of catabolite inactivation. We have cloned the CIF1 gene by complementation of function and located it in a 2.75 kb SphI-BstEII fragment situated at ca. 18 kb centromere distal of LYS2 and ca. 80 kb centromere proximal of TYR1 on chromosome II. Southern analysis demonstrated that CIF1 is present in a single copy in the yeast genome. Northern analysis revealed that the corresponding mRNA of 1.8 kb is more abundant in cells grown on galactose than in those grown on glucose. A protein of ca. 54 kDa was predicted from the open reading frame in the sequenced fragment. In strains carrying the cif1 mutation the intracellular concentration of ATP decreased immediately after addition of glucose while the intracellular concentration of cAMP did not increase. cAMP concentration increased in response to galactose or 2,4-dinitrophenol. Disruption of BCY1 or overexpression of CDC25 in a cif1 background did not restore growth on glucose, suggesting that the absence of cAMP signal is not the primary cause of lack of growth on glucose. Complementation tests showed that cif1 is not allelic to fdp1 although the two genes seem to be functionally related.