Normal Vegetative Growth Research Articles

Multiple Roles of a Heterotrimeric G-Protein γ-Subunit in Governing Growth and Development of Aspergillus nidulans

Vegetative growth signaling in the filamentous fungus Aspergillus nidulans is primarily mediated by the heterotrimeric G-protein composed of FadA (G alpha), SfaD (G beta), and a presumed G gamma. Analysis of the A. nidulans genome identified a single gene named gpgA encoding a putative G gamma-subunit. The predicted GpgA protein consists of 90 amino acids showing 72% similarity with yeast Ste18p. Deletion (delta) of gpgA resulted in restricted vegetative growth and lowered asexual sporulation. Moreover, similar to the delta sfaD mutant, the delta gpgA mutant was unable to produce sexual fruiting bodies (cleistothecia) in self-fertilization and was severely impaired with cleistothecial development in outcross, indicating that both SfaD and GpgA are required for fruiting body formation. Developmental and morphological defects caused by deletion of flbA encoding an RGS protein negatively controlling FadA-mediated vegetative growth signaling were suppressed by delta gpgA, indicating that GpgA functions in FadA-SfaD-mediated vegetative growth signaling. However, deletion of gpgA could not bypass the need for the early developmental activator FluG in asexual sporulation, suggesting that GpgA functions in a separate signaling pathway. We propose that GpgA is the only A. nidulans G gamma-subunit and is required for normal vegetative growth as well as proper asexual and sexual developmental progression.

Genetic mapping of Eef1, a major effect QTL for early flowering in Eucalyptus grandis

An early flowering mutant plant of Eucalyptus grandis with normal vegetative growth was found in a nursery in northern Brazil. This mutant plant flowers at approximately 90 days from germination. A cross between a wild-type (normal flowering) tree and the mutant was carried out, generating a progeny of 88 individuals where early flowering segregated in an approximate 1:1 ratio. A genome scan with 100 microsatellite markers distributed across the genome was carried out using bulk segregant analysis (BSA) on two contrasting bulks of 15 plants each. Linkages (LOD>3.0) with a major effect early flowering quantitative trait locus (QTL) were detected and confirmed by a full scale cosegregation analysis for markers EMBRA27, EMBRA60, EMBRA164, EMBRA158, EMBRA91, and EMBRA65. A localized linkage map involving the six loci and the early flowering QTL named Eucalyptus early flowering 1 (Eef1) was constructed belonging to linkage group #2 in the existing microsatellite reference map. The Eef1 locus was mapped between markers EMBRA27 and EMBRA164, with distances of 21.8 and 6.4 cM, respectively. In introgression experiments, these two markers could be successfully used with an expected precision of 98% to select plants carrying the Eef1 mutant allele, assuming no recombination interference in the genomic segment. Early flowering could be a very useful trait both in breeding as well as experimental genetics of Eucalyptus.

Characterization of a Small Heat Shock Protein, Mx Hsp16.6, of Myxococcus xanthus

A number of heat shock proteins in Myxococcus xanthus were previously identified by two-dimensional (2D) gel electrophoresis. One of these protein was termed Mx Hsp16.6, and the gene encoding Mx Hsp16.6 was isolated. Mx Hsp16.6 consists of 147 amino acid residues and has an estimated molecular weight of 16,642, in accordance with the apparent molecular mass in the 2D gel. An alpha-crystallin domain, typically conserved in small heat shock proteins, was found in Mx Hsp16.6. Mx Hsp16.6 was not detected during normal vegetative growth but was immediately induced after heat shock. Expression of the hsp16.6 gene was not induced by other stresses, such as starvation, oxidation, and high osmolarity. Mx Hsp16.6 was mostly localized in particles formed after heat shock and precipitated by low-speed centrifugation. Furthermore, Mx Hsp16.6 was detected in highly electron-dense particles in heat-shocked cells by immunoelectron microscopy, suggesting that it forms large complexes with heat-denatured proteins. An insertion mutation in the hsp16.6 gene resulted in lower viability during heat shock and lower acquired thermotolerance. Therefore, it is likely that Mx Hsp16.6 plays critical roles in the heat shock response in M. xanthus.

Molecular and Functional Analyses of poi-2 , a Novel Gene Highly Expressed in Sexual and Perithecial Tissues of Neurospora crassa

The poi-2 gene is highly and specifically expressed in starved and sexual tissues of the filamentous fungus Neurospora crassa. It encodes a 27-kDa protein, as shown by in vitro transcription and translation. The POI2 protein contains a hydrophobic signal sequence at the amino terminus followed by novel 16 tandem repeats of 13 to 14 amino acid residues; all repeats are separated by Kex2 processing sites. Repeat-induced point mutation (RIP)-mediated gene disruption was used to generate poi-2 mutants, and the mutated sequences showed either one of two distinct patterns: typical RIPs (GC-to-AT transitions) or insertion-deletion (indel) mutations. Although the poi-2 strains contained numerous mutations, all retained intact open reading frames (ORFs) of various lengths. They showed greatly reduced vegetative growth and protoperithecial formation and low viability of their sexual progeny. All poi-2 mutants had similar defects in male fertility and the mating response, but the nature of female fertility defects varied and corresponded to the length of the residual poi-2 ORF. Mutants with ORFs of approximately normal length occasionally completed sexual development and produced viable ascospores, while a mutant with a severely truncated ORF was female sterile due to its inability to form protoperithecia. Thus, poi-2 is essential for differentiation of female reproductive structures and perithecial development as well as for normal vegetative growth. The POI2 protein is involved in the mating response, probably as a component in the pathway rather than as a pheromone.

Molecular and functional characterization of a fructose specific transporter from the gray mold fungus Botrytis cinerea

In the gray mold fungus Botrytis cinerea, spore germination and plant infection are stimulated in the presence of nutrients, in particular sugars. Applied at micromolar concentrations, fructose is a more potent inducer of germination than glucose. To test whether preferred fructose uptake is responsible for this effect, and to study the mechanism of fructose transport in B. cinerea, a gene ( frt1) encoding a fructose transporter was cloned. FRT1 is highly similar to recently identified fructose transporters of yeasts, but much less to other fungal hexose transporters characterized so far. By using a hexose uptake deficient yeast strain for expression, FRT1 was found to be a high affinity proton coupled symporter specific for fructose but not for glucose. B. cinerea frt1 disruption mutants were created and showed normal vegetative growth and plant infection, but a delay in fructose-induced germination when compared to wild-type. Sugar uptake experiments with both wild-type and mutant conidia showed a higher affinity for glucose than for fructose. Thus, we propose that the specific effect of fructose on germination is not due to transport but rather to an as yet unknown intracellular sensing.

Arabidopsis trehalose-6-phosphate synthase 1 is essential for normal vegetative growth and transition to flowering.

In resurrection plants and yeast, trehalose has a function in stress protection, but the absence of measurable amounts of trehalose in other plants precludes such a function. The identification of a trehalose biosynthetic pathway in angiosperms raises questions on the function of trehalose metabolism in nonresurrection plants. We previously identified a mutant in the Arabidopsis trehalose biosynthesis gene AtTPS1. Plants homozygous for the tps1 mutation do not develop mature seeds (Eastmond et al., 2002). AtTPS1 expression analysis and the spatial and temporal activity of its promoter suggest that this gene is active outside the seed-filling stage of development as well. A generally low expression is observed in all organs analyzed, peaking in metabolic sinks such as flower buds, ripening siliques, and young rosette leaves. The arrested tps1/tps1 embryonic state could be rescued using a dexamethasone-inducible AtTPS1 expression system enabling generation of homozygous mutant plants. When depleted in AtTPS1 expression, such mutant plants show reduced root growth, which is correlated with a reduced root meristematic region. Moreover, tps1/tps1 plants are retarded in growth and remain generative during their lifetime. Absence of Trehalose-6-Phosphate Synthase 1 in Arabidopsis plants precludes transition to flowering.

REN1 is required for development of microconidia and macroconidia, but not of chlamydospores, in the plant pathogenic fungus Fusarium oxysporum.

The filamentous fungus Fusarium oxysporum is a soil-borne facultative parasite that causes economically important losses in a wide variety of crops. F. oxysporum exhibits filamentous growth on agar media and undergoes asexual development producing three kinds of spores: microconidia, macroconidia, and chlamydospores. Ellipsoidal microconidia and falcate macroconidia are formed from phialides by basipetal division; globose chlamydospores with thick walls are formed acrogenously from hyphae or by the modification of hyphal cells. Here we describe rensa, a conidiation mutant of F. oxysporum, obtained by restriction-enzyme-mediated integration mutagenesis. Molecular analysis of rensa identified the affected gene, REN1, which encodes a protein with similarity to MedA of Aspergillus nidulans and Acr1 of Magnaporthe grisea. MedA and Acr1 are presumed transcription regulators involved in conidiogenesis in these fungi. The rensa mutant and REN1-targeted strains lack normal conidiophores and phialides and form rod-shaped, conidium-like cells directly from hyphae by acropetal division. These mutants, however, exhibit normal vegetative growth and chlamydospore formation. Nuclear localization of Ren1 was verified using strains expressing the Ren1-green fluorescent protein fusions. These data strongly suggest that REN1 encodes a transcription regulator required for the correct differentiation of conidiogenesis cells for development of microconidia and macroconidia in F. oxysporum.

AtCPSF73-II gene encoding an Arabidopsis homolog of CPSF 73 kDa subunit is critical for early embryo development

We have identified and genetically characterized an Arabidopsis thaliana gene encoding a homolog of the Cleavage and Polyadenylation Specificity Factor (CPSF). This gene, named AtCPSF73-II, has been found to have a critical role in development by loss-of-function analysis using a Dissociation (Ds) insertion line SGT1922. The homozygous SGT1922 plants were lethal, but the heterozygous plants, while retaining their normal vegetative growth, displayed empty seed spaces as well as aborted seeds with embryos arrested at the globular stage. Genetic analysis indicated that the disruption of the AtCPSF73-II gene in SGT1922 plants caused severe reduction in genetic transmission of female gametes due to a loss of fertility, while the transmission of male gametes was normal. Two independent heterozygous lines with T-DNA insertion on the AtCPSF73-II gene also showed the similar phenotype. Gene expression analysis demonstrated that AtCPSF73-II was preferentially expressed in flowers. Protein sequence analysis revealed a group of AtCPSF73-II homologs with unknown function in animals, but not in yeast, which suggested a potential important function of this group of genes in the development of multicellular organisms.

Members of the Arabidopsis-SKP1-like gene family exhibit a variety of expression patterns and may play diverse roles in Arabidopsis.

Ubiquitin-mediated proteolysis by the proteasome is a critical regulatory mechanism controlling many biological processes. In particular, SKP1, cullin/CDC53, F-box protein (SCF) complexes play important roles in selecting substrates for proteolysis by facilitating the ligation of ubiquitin to specific proteins. In plants, SCF complexes have been found to regulate auxin responses and jasmonate signaling and may be involved in several other processes, such as flower development, circadian clock, and gibberellin signaling. Although 21 Skp1-related genes, called Arabidopsis-SKP1-like (ASK), have been uncovered in the Arabidopsis genome, ASK1 is the only gene that has been analyzed genetically. As a first step toward understanding their functions, we tested for expression of 20 ASK genes using reverse transcription-polymerase chain reaction experiments. Also, we examined the expression patterns of 11 ASK genes by in situ hybridizations. The ASK genes exhibit a spectrum of expression levels and patterns, with a large subset showing expression in the flower and/or fruit. In addition, the ASK genes that have similar sequences tend to have similar expression patterns. On the basis of the expression results, we selectively suppressed the expression of a few ASK genes using RNA interference. Compared with the ask1 mutant, the strong ASK1 RNA interference (RNAi) line exhibited similar or enhanced phenotypes in both vegetative and floral development, whereas ASK11 RNAi plants had normal vegetative growth but mild defects in flower development. The diverse expression patterns and distinct defects observed in RNAi plants suggest that the ASK gene family may collectively perform a range of functions and may regulate different developmental and physiological processes.

Myxococcus xanthus socD500에 의한 포자 형성 및 CsgA신호에 특이적 유전자의 발현에 관한 연구

군집을 이루어 생활을 하는 세균류의 하나인 M. xanthus의 csgA 유전자는 세포 표면 단백질을 암호화하는데 이 단백질은 M. xanthus의 자실체 및 포자 형성을 수반하는 발생 (development)에 필수적이다. csgA 돌연변이들은 정상적인 성장을 보이지만, 발생 과정에서 자실체 및 포자 형성이 불가능하다. 또한, CsgA 세포간 기인한 신호 전달체계에 의해서 유발되는 CsgA 특이적 유전자들의 발현이 없거나 감소한다. socD500돌연변이는, csgA 돌연변이체로부터 자실체 혹은 포자 형성을 회복하게 해주는 2차 돌연변이 중의 하나로서, csgA 돌연변이체의 포자 형성을 회복하도록 한다. socD500에 의한 포자 형성은 영양원의 고갈 및 자실체의 형성이 없이도, 단순히 성장 온도를 <TEX>$32^{\circ}C$</TEX>에서 <TEX>$15^{\circ}C$</TEX>로 낮추는 것이 의해서 이루어진다. 이런 과정을 거쳐 형성된 포자의 구조를 전자현미경으로 관찰한 결과 정상 포자와는 다르게 단지 얇은 여러 겹의 막들이 존재하였다. 또한 socD500 돌연변이체에서 10개의 CsgA 특이적 유전자들의 발현율을 측정한 결과, 자실체 형성을 수반하는 정상적인 발생시에만 발현하는 ΩDK4506 및 ΩDK4406 유전자들이 <TEX>$15^{\circ}C$</TEX>에서 높게 발현되는 것으로 나타났다. 이 결과는 socD500은 CsgA에 특이적인 신호 전달체계에 관련된 일부 유전자들의 발현을 조절하는 역할에 관련되었다는 것을 알 수가 있었다. Myxococcus xanthus is a Gram negative, rod-shaped, soil bacterium that displays a social behaviors, and multicellular development upon nutrient deprivation. The csgA gene encoding a cell surface protein is essential for developmental behaviors including rippling, aggregation, fruiting body formation and sporulation. csgA mutants show normal vegetative growth, but lack all these developmental phenotypes. Expression of the CsgA (C-signal) specific genes are eliminated or dramatically reduced in csgA mutants. In order to identify components of C-signal transduction pathway, second site mutations were introduced into csgA mutants and were identified which can fully or partially restore development of csgA mutants (Rhie, H. G. et. al. 1989. J. Bacteriol. 171, 3268-3276). One of such csgA suppressor mutations, socD500 restores only sporulation to csgA mutants at 15<TEX>$^{\circ}C$</TEX>. The socD500 mutaion however eliminates the three basic developmental requirements, starvation, high cell density and a solid surface. Only sporulation, not accompanied with fruiting body formation is induced simply by shifting the temperature of vegetatively growing cells from <TEX>$32^{\circ}C$</TEX> to <TEX>$15^{\circ}C$</TEX>. Spores induced by socD500 mutation is not as thick as that of wild-type fruiting body. In socD500 genetic background, two of ten C-signal dependent genes, <TEX>$\Omega$</TEX>DK4506 and <TEX>$\Omega$</TEX>DK4406 are more highly expressed in growing cells at <TEX>$15^{\circ}C$</TEX>. These results indicate that the socD500 mutation may be partly involved in the regulation of expression of two C-signal dependent genes and genes for sporulation in this transduction pathway.

Clap1, a gene encoding a copper-transporting ATPase involved in the process of infection by the phytopathogenic fungus Colletotrichum lindemuthianum

A screen for insertional mutants of Colletrichum lindemuthianum, the causative agent of common bean anthracnose, led to the identification of a non-pathogenic, lightly colored transformant. This mutant is unable to induce disease symptoms on intact or wounded primary leaves of seedlings and plantlets of Phaseolus vulgaris. In vitro, it exhibits normal vegetative growth, sporulation and conidial germination, but the cultures remain beige instead of becoming black. Microscopic examination revealed that this mutant forms fewer appressoria than the wild-type strain, and these are misshapen and poorly melanized. Molecular analyses indicated that the mutagenic plasmid had targeted clap1, a gene encoding a putative copper-transporting ATPase sharing 35% identity with the human Menkes and Wilson proteins and the product of the CCC2 gene of Saccharomyces cerevisiae. Complementation of the non-pathogenic beige mutant with a wild-type allele of clap1 restored both pathogenicity and pigmentation. Conversely, replacement of the wild-type allele with a disrupted clap1 gene gave rise to non-pathogenic beige transformants. Compared with the wild-type strain, extracts from clap1 mutants were found to have very low levels of phenol oxidase activity. These observations suggest that the clap1 gene product may be involved in the pathogenicity of C. lindemuthianum strains because of its role in delivering copper to secreted cuproenzymes, such as the phenol oxidases that mediate the polymerization of 1,8-dihydroxynaphthalene to melanin.

SPO14 separation-of-function mutations define unique roles for phospholipase D in secretion and cellular differentiation in Saccharomyces cerevisiae.

In Saccharomyces cerevisiae, phospholipase D (PLD), encoded by the SPO14 gene, catalyzes the hydrolysis of phosphatidylcholine, producing choline and phosphatidic acid. SPO14 is essential for cellular differentiation during meiosis and is required for Golgi function when the normal secretory apparatus is perturbed (Sec14-independent secretion). We isolated specific alleles of SPO14 that support Sec14-independent secretion but not sporulation. Identification of these separation-of-function alleles indicates that the role of PLD in these two physiological processes is distinct. Analyses of the mutants reveal that the corresponding proteins are stable, phosphorylated, catalytically active in vitro, and can localize properly within the cell during meiosis. Surprisingly, the separation-of-function mutations map to the conserved catalytic region of the PLD protein. Choline and phosphatidic acid molecular species profiles during Sec14-independent secretion and meiosis reveal that while strains harboring one of these alleles, spo14S-11, hydrolyze phosphatidylcholine in Sec14-independent secretion, they fail to do so during sporulation or normal vegetative growth. These results demonstrate that Spo14 PLD catalytic activity and cellular function can be differentially regulated at the level of phosphatidylcholine hydrolysis.

The arabidopsis cell plate-associated dynamin-like protein, ADL1Ap, is required for multiple stages of plant growth and development.

Dynamin and dynamin-like proteins are GTP-binding proteins involved in vesicle trafficking. In soybean, a 68-kD dynamin-like protein called phragmoplastin has been shown to be associated with the cell plate in dividing cells (Gu and Verma, 1996). Five ADL1 genes encoding dynamin-like proteins related to phragmoplastin have been identified in the completed Arabidopsis genome. Here we report that ADL1Ap is associated with punctate subcellular structures and with the cell plate in dividing cells. To assess the function of ADL1Ap we utilized a reverse genetic approach to isolate three separate Arabidopsis mutant lines containing T-DNA insertions in ADL1A. Homozygous adl1A seeds were shriveled and mutant seedlings arrested soon after germination, producing only two leaf primordia and severely stunted roots. Immunoblotting revealed that ADL1Ap expression was not detectable in the mutants. Despite the loss of ADL1Ap, the mutants did not display any defects in cytokinesis, and growth of the mutant seedlings could be rescued in tissue culture by the addition of sucrose. Although these sucrose-rescued plants displayed normal vegetative growth and flowered, they set very few seeds. Thus, ADL1Ap is critical for several stages of plant development, including embryogenesis, seedling development, and reproduction. We discuss the putative role of ADL1Ap in vesicular trafficking, cytokinesis, and other aspects of plant growth.

A MAP kinase of the vascular wilt fungus Fusarium oxysporum is essential for root penetration and pathogenesis

The soil-borne vascular wilt fungus Fusarium oxysporum infects a wide variety of plant species by directly penetrating roots, invading the cortex and colonizing the vascular tissue. We have identified fmk1, encoding a mitogen-activated protein kinase (MAPK) of F. oxysporum that belongs to the yeast and fungal extracellular signal-regulated kinase (YERK1) subfamily. Targeted mutants of F. oxysporum f. sp. lycopersici carrying an inactivated copy of fmk1 have lost pathogenicity on tomato plants but show normal vegetative growth and conidiation in culture. Colonies of the fmk1 mutants are easily wettable, and hyphae are impaired in breaching the liquid-air interface, suggesting defects in surface hydrophobicity. Fmk1 mutants also show reduced invasive growth on tomato fruit tissue and drastically reduced transcript levels of pl1 encoding the cell wall-degrading enzyme pectate lyase. Conidia of the mutants germinating in the tomato rhizosphere fail to differentiate penetration hyphae, resulting in greatly impaired root attachment. The orthologous MAPK gene Pmk1 from the rice leaf pathogen Magnaporthe grisea complements invasive growth and partially restores surface hydrophobicity, root attachment and pathogenicity in an fmk1 mutant. These results demonstrate that FMK1 controls several key steps in the pathogenesis of F. oxysporum and suggest a fundamentally conserved role for the corresponding MAPK pathway in soil-borne and foliar plant pathogens.

Isolation and use of a homologous histone H4 promoter and a ribosomal DNA region in a transformation vector for the oil-producing fungus Mortierella alpina.

Mortierella alpina was transformed successfully to hygromycin B resistance by using a homologous histone H4 promoter to drive gene expression and a homologous ribosomal DNA region to promote chromosomal integration. This is the first description of transformation in this commercially important oleaginous organism. Two pairs of histone H3 and H4 genes were isolated from this fungus. Each pair consisted of one histone H3 gene and one histone H4 gene, transcribed divergently from an intergenic promoter region. The pairs of encoded histone H3 or H4 proteins were identical in amino acid sequence. At the DNA level, each histone H3 or H4 open reading frame showed 97 to 99% identity to its counterpart but the noncoding regions had little sequence identity. Unlike the histone genes from other filamentous fungi, all four M. alpina genes lacked introns. During normal vegetative growth, transcripts from the two histone H4 genes were produced at approximately the same level, indicating that either histone H4 promoter could be used in transformation vectors. The generation of stable, hygromycin B-resistant transformants required the incorporation of a homologous ribosomal DNA region into the transformation vector to promote chromosomal integration.

Yeast homolog of human SAG/ROC2/Rbx2/Hrt2 is essential for cell growth, but not for germination: chip profiling implicates its role in cell cycle regulation.

In an attempt to understand the signaling pathway mediating redox-induced apoptosis, we cloned SAG, an evolutionarily conserved zinc RING finger gene that, when overexpressed, protects cells from apoptosis induced by redox agents. Here we report functional characterization of SAG by the use of yeast genetics approach. Targeted disruption of ySAG, yeast homolog of human SAG, and subsequent tetrad analysis revealed that ySAG is required for yeast viability. Complementation experiment showed that the lethal phenotype induced by the ySAG deletion is fully rescued by wildtype SAG, but not by several hSAG mutants. Complementation experiment has also confirmed that ySAG is essential for normal vegetative growth, rather than being required for sporulation. Furthermore, cell death induced by SAG deletion was accompanied by cell enlargement and abnormal cell cycle profiling with an increased DNA content. Importantly, SAG was found to be the second family member of Rbx (RING box protein) or ROC (Regulator of cullins) or Hrt that is a component of SCF E3 ubiquitin ligase. Indeed, like ROC1/Rbx1/Hrt1, SAG binds to Cul1 and SAG-Cul1 complex has ubiquitin ligase activity to promote poly-ubiquitination of E2/Cdc34. This ligase activity is required for complementation of death phenotype induced by ySAG disruption. Finally, chip profiling of the entire yeast genome revealed induction of several G1/S as well as G2/M checkpoint control genes upon SAG withdrawal. Thus, SAG appears to control cell cycle progression in yeast by promoting ubiquitination and degradation of cell cycle regulatory proteins. Oncogene (2000) 19, 2855 - 2866

Ornithine Decarboxylase of Stagonospora (Septoria) nodorum Is Required for Virulence toward Wheat

A knockout strain of Stagonospora (Septoria) nodorum lacking the single ornithine decarboxylase (ODC) allele has been created by targeted gene replacement. A central region of the S. nodorum ODC gene was isolated by polymerase chain reaction using degenerate oligonucleotides and used to probe a lambda genomic library. The gene was sequenced and the encoded ODC protein sequence was shown to be similar to those from other fungi. The functionality of the S. nodorum ODC was confirmed by complementation of an Aspergillus nidulans mutant (puA) strain devoid of ODC activity, restoring growth in the absence of exogenous polyamines. Sporulation of the transformants was reduced suggesting abberant regulation of the S. nodorum gene in A. nidulans. Transformation-mediated gene replacement was used to create strains which were auxotrophic for putrescine and lack ODC coding sequences. Pathogenicity studies on these mutants showed that they are greatly reduced in virulence compared with non-disrupted transformants. This confirms that the strains carrying an ODC disruption cannot obtain sufficient polyamines from the host plant for normal growth and, thus, that fungal ODC may be a suitable target for chemical intervention.

Function of a principal Na(+)/H(+) antiporter, ShaA, is required for initiation of sporulation in Bacillus subtilis.

ShaA (sodium/hydrogen antiporter, previously termed YufT [or NtrA]), which is responsible for Na(+)/H(+) antiporter activity, is considered to be the major Na(+) excretion system in Bacillus subtilis. We found that a shaA-disrupted mutant of B. subtilis shows impaired sporulation but normal vegetative growth when the external Na(+) concentration was increased in a low range. In the shaA mutant, sigma(H)-dependent expression of spo0A (P(S)) and spoVG at an early stage of sporulation was sensitive to external NaCl. The level of sigma(H) protein was reduced by the addition of NaCl, while the expression of spo0H, which encodes sigma(H), was little affected, indicating that posttranscriptional control of sigma(H) rather than spo0H transcription is affected by the addition of NaCl in the shaA mutant. Since this mutant is considered to have a diminished ability to maintain a low internal Na(+) concentration, an increased level of internal Na(+) may affect posttranscriptional control of sigma(H). Bypassing the phosphorelay by introducing the sof-1 mutation into this mutant did not restore spo0A (P(S)) expression, suggesting that disruption of shaA affects sigma(H) accumulation, but does not interfere with the phosphorylation and phosphotransfer reactions of the phosphorelay. These results suggest that ShaA plays a significant role at an early stage of sporulation and not only during vegetative growth. Our findings raise the possibility that fine control of cytoplasmic ion levels, including control of the internal Na(+) concentration, may be important for the progression of the sporulation process.

Cell growth: A Single Bag of Tricks for Yeast

The already impressive capacity of yeast to use very similar Map kinase (MAPK) signaling pathways to mediate distinct biological processes becomes even more amazing with a report from Lee and Elion. The MAPKKK/Ste11 and other downstream components were thought to be dedicated to mating and invasive growth signaling pathways and to be inactive during normal vegetative growth. The authors show that Ste11 and other components shared by the mating and invasive growth pathway also function to promote vegetative growth. Hence, yeast appear to accommodate a variety of responses by using appropriate members from a single repertoire of signaling components. Lee, B.N., and Elion, E.A. (1999) The MAPKKK Ste11 regulates vegetative growth through a kinase cascade of shared signaling components. Proc. Natl. Acad. Sci. U.S.A. 96 : 12679-12684. [Abstract] [Full Text]

Cell growth: A Single Bag of Tricks for Yeast

The already impressive capacity of yeast to use very similar Map kinase (MAPK) signaling pathways to mediate distinct biological processes becomes even more amazing with a report from Lee and Elion. The MAPKKK/Ste11 and other downstream components were thought to be dedicated to mating and invasive growth signaling pathways and to be inactive during normal vegetative growth. The authors show that Ste11 and other components shared by the mating and invasive growth pathway also function to promote vegetative growth. Hence, yeast appear to accommodate a variety of responses by using appropriate members from a single repertoire of signaling components.Lee, B.N., and Elion, E.A. (1999) The MAPKKK Ste11 regulates vegetative growth through a kinase cascade of shared signaling components. Proc. Natl. Acad. Sci. U.S.A. 96: 12679-12684. [Abstract] [Full Text]