Molecular Interactions Between Flowering Time and Abiotic Stress Pathways.

Plants have adapted to environmental changes and stresses over generations. The decision of transition from the vegetative to reproductive stage is critical, particularly under unfavorable conditions. Thus, plants appear to have developed mechanisms by which environmental factors or inputs are transmitted to stress response signaling pathways to confer tolerance and are simultaneously integrated into flowering regulation pathways (photoperiod, vernalization, autonomous, and gibberellic acid signaling) to propagate the next generation. In this review, we summarize how abiotic stresses influence, induce, or delay flowering time, particularly in the long-day plant Arabidopsis. Four major modes including FLOWERING LOCUS C (FLC), CONSTANS (CO), DELLA, and GIGANTEA (GI), which serve as hubs that integrate stress signals for regulating flowering time, are introduced. GI, a mediator of the photoperiod floral pathway and circadian clock, is involved in various biological processes and thus controls stress response directly through interaction with stress-responsive components and indirectly through association with circadian clock components.

Salt-Sensitive Mutants of Chlamydomonas reinhardtii Isolated after Insertional Tagging.

We describe the isolation of salt-sensitive Chlamydomonas reinhardtii mutants by insertional mutagenesis using the nitrate reductase (Nit1) gene. The plasmid pMN24, containing Nit1, was used for transformation of 305CW15 (nit1 cw15 mt+), and transformants were selected for complementation of the nit- phenotype. From 6875 nit+ colonies, four transformants (S4, S18, S46, and S66) were isolated that exhibited both Na+ and Li+ sensitivity (sod-), and another transformant (S33) was selected that exhibited sensitivity to Li+ but not Na+ (lit-) based on relative growth comparisons with the wild-type strain. S33, S46, and S66 were no more growth inhibited by sorbitol than was 305CW15. In comparison, S4 and S18 exhibited substantial growth inhibition in medium supplemented with sorbitol. Genetic analyses indicated that the salt-sensitive mutants were each defective in a single recessive gene. The mutant genes in S4 (sod1), S33 (lit1), and S66 (sod3) are linked to a functional copy of Nit1 and are presumably tagged with a pMN24 insertion.

Functional conservation between yeast and plant endosomal Na(+)/H(+) antiporters.

Vacuolar compartmentation of Na(+) is an essential mechanism for salinity tolerance since it lowers cytosolic Na(+) levels while contributing to osmotic adjustment for cell turgor and expansion. The AtNHX1 protein of Arabidopsis thaliana substituted functionally for ScNHX1, the endosomal Na(+)/H(+) antiporter of yeast. Ion tolerance conferred by AtNHX1 and ScNHX1 correlated with ion uptake into an intracellular pool that was energetically dependent on the vacuolar (H(+))ATPase. AtNHX1 localized to vacuolar membrane fractions of yeast. Hence, both transporters share an evolutionarily conserved function in Na(+) compartmentation. AtNHX1 mRNA levels were upregulated by ABA and NaCl treatment in leaf but not in root tissue.

Similar short elements in the 5' regions of the STA2 and SGA genes from Saccharomyces cerevisiae.

The 5' region of the SGA and STA2 genes, encoding the intra- and extracellular glucoamylases, respectively, from Saccharomyces cerevisiae have been sequenced. In addition, the transcription initiation sites have been determined. Four distinct short elements (named I to IV) were found in both genes. Element III has the consensus sequence PuCATTTAPiG with a bilateral symmetry around the central T, and is present in both genes as a direct repeat. This motive seems responsible for the coregulation of STA2 and SGA by the repressor STA10 gene of S. cerevisiae.

Impact of the human immunodeficiency virus on the epidemiology of tuberculosis in area 15 of the Valencian community in Spain.

SETTING: Area 15 in Valencia. OBJECTIVES: To describe the epidemiology (1987-2001) of tuberculosis (TB) in human immunodeficiency virus (HIV) patients. METHODS: Study of annual incidence, age distribution, excess cases attributed to HIV, etiological risk fraction (ERF), population attributable fraction (PAF) and f factor. RESULTS: Of 476 cases diagnosed, 459 were TB, 16 environmental and one mixed; 76% of environmental cases were HIV-positive (P < 0.001). There was a mean annual TB incidence of 24.6/100000, with an annual reduction of 4%. Seventy-three patients were HIV coinfected (16%) (mean incidence 3834/100 000 seropositives). The principal risk factor was drug use (59%) for HIV+ and contact with TB for HIV-. We found no difference in pulmonary or extra-pulmonary location between groups, contrary to mixed cases (P < 0.001). In HIV+ there was a lower frequency of infiltrates (P < 0.001) and cavitation (P < 0.01), and a higher frequency of adenitis (P < 0.001), miliary or nodular pattern and normal X-ray (P < 0.001). Seropositives had a 174 times higher probability of developing TB. The mean ERF attributed to HIV was 99%, the PAF was 16% and the f factor was 1.19. Highly active antiretroviral therapy (HAART) reduced the risk of TB in HIV+ by 80%. CONCLUSIONS: TB has continued its decline, although HIV generated an excess of cases in the 1990s. HAART has reduced the TB risk in HIV+ and possibly the overall rate of TB.

Virilization of a female infant due to an adrenal tumor.

We report here the case of a 22-month-old girl with virilization due to a potentially malignant adrenal tumor. She presented with clitoromegaly and growth of pubic hair, first noticed at birth. The clinical picture, hormonal profile, and pathologic findings are described. The practical aspects of the differential diagnosis and treatment are illustrated.

[A case of rheumatoid factor associated with pancreatic carcinoma]. / Un caso de factor reumatoide asociado a carcinoma de páncreas.

A case of adenocarcinoma of pancreas's tail, whose first manifestation was a prolonged fever syndrome, is presented. The only laboratory feature was the presence of a rheumatoid factor which appeared weeks before the diagnosis was made. There was no other pathology to justify its presence. The levels of RF decreased after the extirpation of the tumor and, coincidentally, with the clinical improvement. The level of RF was normal 4 months after the operation. The presence of RF in neoplasia and its possible relation to tumoral evolution is discussed.

Structure of a plasma membrane H+-ATPase gene from the plant Arabidopsis thaliana.

Physiological and biochemical studies have suggested that the plant plasma membrane H+-ATPase controls many important aspects of plant physiology, including growth, development, nutrient transport, and stomata movements. We have started the genetic analysis of this enzyme by isolating both genomic and cDNA clones of an H+-ATPase gene from Arabidopsis thaliana. The cloned gene is interrupted by 15 introns, and there is partial conservation of exon boundaries with respect to animal (Na+/K+)- and Ca2+-ATPases. In general, the relationship between exons and the predicted secondary and transmembrane structure of different ATPases with phosphorylated intermediate support a somewhat degenerate correspondence between exons and structural modules. The predicted amino acid sequence of the plant H+-ATPase is more closely related to fungal and protozoan H+-ATPases than to bacterial K+-ATPases or to animal (Na+/K+)-, (H+/K+)-, and Ca2+-ATPases. There is evidence for the existence of at least three isoforms of the plant H+-ATPase gene. These results open the way for a molecular approach to the structure and function of the plant proton pump.

Cloning of the STA2 and SGA genes encoding glucoamylases in yeasts and regulation of their expression by the STA10 gene of Saccharomyces cerevisiae.

The Saccharomyces STA2 and SGA genes, encoding the extracellular and intracellular sporulation-specific glucoamylase respectively, have been cloned and their transcription and regulation studied. The STA2 gene differs from the SGA gene in that it contains an extra piece of DNA, which encodes the domain for exportation of the extracellular glucoamylase. The STA2 gene produces a single 2.85 kb transcript. Transcription of the SGA gene is initiated from two different sites, yielding two transcripts of 1.95 and 2.40 kb. Transcription of both STA2 and SGA genes is repressed by the STA10 gene of Saccharomyces cerevisiae.

Immunocytolocalization of Plasma Membrane H-ATPase.

The localization of plasma membrane H(+)-ATPase has been studied at the optical microscope level utilizing frozen and paraffin sections of Avena sativa and Pisum sativum, specific anti-ATPase polyclonal antibody, and second antibody coupled to alkaline phosphatase. In leaves and stems the ATPase is concentrated at the phloem, supporting the notion that it generates the driving force for phloem loading. In roots the ATPase is concentrated at both the periphery (rootcap and epidermis) and at the central cylinder, including endodermis and vascular cells. This supports a ;two-pump' mechanism for ion absorption, involving active uptake at the epidermis, symplast transport across the cortex, and active efflux at the xylem. The low ATPase content of root meristem and elongation zone may explain the observed transorgan H(+) currents, which leave nongrowing parts and enter growing tips.

Differential accumulation of S-adenosylmethionine synthetase transcripts in response to salt stress.

NaCl stress causes the accumulation of several mRNAs in tomato seedlings. An upregulated cDNA clone, SAM1, was found to encode a S-adenosyl-L-methionine synthetase enzyme (AdoMet synthetase). Expression of the cDNA SAM1 in a yeast mutant lacking functional SAM genes resulted in high AdoMet synthetase activity and AdoMet accumulation. We show that tomato plants contain at least four SAM isogenes. Clones corresponding to isogenes SAM2 and SAM3 have also been isolated and sequenced. They encode predicted polypeptides 95% and 92% identical, respectively, to the SAM1-encoded AdoMet Synthetase. RNA hybridization analysis showed a differential response of SAM genes to salt and other stress treatments. SAM1 and SAM3 mRNAs accumulated in the root in response to NaCl, mannitol or ABA treatments. SAM1 mRNA accumulated also in leaf tissue. These increases of mRNA level were apparent as soon as 8 h after the initiation of the salt treatment and were maintained for at least 3 days. A possible role for AdoMet synthetases in the adaptation to salt stress is discussed.

Purification and characterization of a hygromycin B phosphotransferase from Streptomyces hygroscopicus.

A hygromycin B phosphotransferase activity from Streptomyces hygroscopicus has been highly purified by ammonium sulphate fractionation followed by affinity column chromatography through Sepharose-6B-hygromycin-B. The combined active fractions showed a single protein band (41 kDa) when subjected to polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulphate. When gel electrophoresis was performed under non-denaturing conditions, the single protein band promoted in situ phosphorylation of hygromycin B, indicating that this protein corresponded to the purified hygromycin B phosphotransferase. The enzyme has been purified 236-fold and approximate Km values of 0.56 microM for hygromycin B and ATP, respectively, were deduced.

Molecular characterization of glyoxalase-I from a higher plant; upregulation by stress.

A cDNA, GLX1, encoding glyoxalase-I was isolated by differential screening of salt-induced genes in tomato. Glyoxalases-I and -II are ubiquitous enzymes whose functions are not clearly understood. They may serve to detoxify methylglyoxal produced from triosephosphates in all cells. The protein encoded by GLX1 shared 49.4% and 58.5% identity with glyoxalase-I isolated from bacteria and human, respectively. Furthermore, yeast cells expressing GLX1 showed a glyoxalase-I specific activity 20-fold higher than non-transformed cells. Both GLX1 mRNA and glyoxalase-I polypeptide levels increased 2- to 3-fold in roots, stems and leaves of plants treated with either NaCl, mannitol, or abscisic acid. Immunohistochemical localization indicated that glyoxalase-I was expressed in all cell types, with preferential accumulation in phloem sieve elements. This expression pattern was not appreciably altered by salt-stress. We suggest that the increased expression of glyoxalase-I may be linked to a higher demand for ATP generation and to enhanced glycolysis in salt-stressed plants.

Phosphate transporters from the higher plant Arabidopsis thaliana.

Two cDNAs (AtPT1 and AtPT2) encoding plant phosphate transporters have been isolated from a library prepared with mRNA extracted from phosphate-starved Arabidopsis thaliana roots, The encoded polypeptides are 78% identical to each other and show high degree of amino acid sequence similarity with high-affinity phosphate transporters of Saccharomyces cerevisiae, Neurospora crassa, and the mycorrhizal fungus Glomus versiforme. The AtPT1 and AtPT2 polypeptides are integral membrane proteins predicted to contain 12 membrane-spanning domains separated into two groups of six by a large charged hydrophilic region. Upon expression, both AtPT1 and AtPT2 were able to complement the pho84 mutant phenotype of yeast strain NS219 lacking the high-affinity phosphate transport activity. AtPT1 and AtPT2 are representatives of two distinct, small gene families in A. thaliana. The transcripts of both genes are expressed in roots and are not detectable in leaves. The steady-state level of their mRNAs increases in response to phosphate starvation.

Biochemical basis of resistance to hygromycin B in Streptomyces hygroscopicus--the producing organism.

Hygromycin B, an aminocyclitol antibiotic that strongly inhibits both 70S and 80S ribosomes, is synthesized by Streptomyces hygroscopicus. Ribosomes from this Gram-positive mycelial bacterium are inhibited in vitro by the antibiotic. In contrast, the streptomycete is highly resistant to the drug in vivo since it possesses hygromycin B phosphotransferase activity. This enzyme has been shown by gel filtration to have a molecular weight of 42000, and to modify its antibiotic substrate to produce 7"-O-phosphoryl-hygromycin B which totally lacks biological activity both in vivo and in vitro.

A tomato cDNA inducible by salt stress and abscisic acid: nucleotide sequence and expression pattern.

We have characterized a new tomato cDNA, TAS14, inducible by salt stress and abscisic acid (ABA). Its nucleotide sequence predicts an open reading frame coding for a highly hydrophilic and glycine-rich (23.8%) protein of 130 amino acids. Southern blot analysis of tomato DNA suggests that there is one TAS14 structural gene per haploid genome. TAS14 mRNA accumulates in tomato seedlings upon treatment with NaCl, ABA or mannitol. It is also induced in roots, stems and leaves of hydroponically grown tomato plants treated with NaCl or ABA. TAS14 mRNA is not induced by other stress conditions such as cold and wounding. The sequence of the predicted TAS14 protein shows four structural domains similar to the rice RAB21, cotton LEA D11 and barley and maize dehydrin genes.