The Arabidopsis floral meristem-identity genes APETALA1 (AP1) and LEAFY (LFY) confer floral identity on developing floral primordia, whereas TERMINAL FLOWER (TFL) is required to repress their expression within shoot and inflorescence meristems. LFY and AP1 are expressed in floral primordia in response to environmental conditions, such as day length, which regulate the onset of flowering, and presumably also in response to the action of genes that influence flowering time. However, the relationship between these flowering-time genes and the floral meristem-identity genes has been difficult to assess because flowering time is determined by several interacting genetic pathways. Here we describe a method to regulate expression of the flowering-time gene CONSTANS (CO) and demonstrate that CO expression is sufficient to trigger flowering, irrespective of day length. In response to CO expression, transcription of LFY and TFL is initiated rapidly, whereas transcription of AP1 occurs much later. We propose that CO acts within a genetic pathway that is sufficient to activate LFY and TFL transcription, but that rapid activation of AP1 requires an additional pathway.

CONSTANS ( CO ) promotes flowering of Arabidopsis in response to long photoperiods. Transgenic plants carrying CO fused with the cauliflower mosaic virus 35S promoter (35S:: CO ) flowered earlier than did the wild type and were almost completely insensitive to length of day. Genes required for CO to promote flowering were identified by screening for mutations that suppress the effect of 35S:: CO . Four mutations were identified that partially suppressed the early-flowering phenotype caused by 35S:: CO . One of these mutations, suppressor of overexpression of CO 1 ( soc1 ), defines a new locus, demonstrating that the mutagenesis approach is effective in identifying novel flowering-time mutations. The other three suppressor mutations are allelic with previously described mutations that cause late flowering. Two of them are alleles of ft , indicating that FT is required for CO to promote early flowering and most likely acts after CO in the hierarchy of flowering-time genes. The fourth suppressor mutation is an allele of fwa , and fwa soc1 35S:: CO plants flowered at approximately the same time as co mutants, suggesting that a combination of fwa and soc1 abolishes the promotion of flowering by CO . Besides delaying flowering, fwa acted synergistically with 35S:: CO to repress floral development after bolting. The latter phenotype was not shown by any of the progenitors and was most probably caused by a reduction in the function of LEAFY . These genetic interactions suggest models for how CO , FWA , FT , and SOC1 interact during the transition to flowering.

Pseudomonas pseudoalcaligenes CECT5344 is a Gram-negative bacterium able to tolerate cyanide and to use it as the sole nitrogen source. We report here the first draft of the whole genome sequence of a P. pseudoalcaligenes strain that assimilates cyanide. Three aspects are specially emphasized in this manuscript. First, some generalities of the genome are shown and discussed in the context of other Pseudomonadaceae genomes, including genome size, G + C content, core genome and singletons among other features. Second, the genome is analysed in the context of cyanide metabolism, describing genes probably involved in cyanide assimilation, like those encoding nitrilases, and genes related to cyanide resistance, like the cio genes encoding the cyanide insensitive oxidases. Finally, the presence of genes probably involved in other processes with a great biotechnological potential like production of bioplastics and biodegradation of pollutants also is discussed.

The effect of pH on bacterial cell-growth and the evolution of extracellular pH triggered by bacterial growth has been monitored for three bacterial strains, Escherichia coli ATCC 25922 and Pseudomonas putida KT2440 as reference strains, and Pseudomonas pseudoalcaligenes CECT 5344 because of its capacity to assimilate cyanide as the sole nitrogen source under alkaline conditions. In a first instance, the influence of the initial pH in the growth curve has been texted in LB-medium adjusted to pH 6, 7 and 8, for E. coli and P. putida, and 7.5, 8.25 and 9 for P. pseudoalcaligenes. Although the initial pH were different, the pH of the extracellular medium at the end of the stationary phase converged to a certain pH that is specific for each bacterium. Similar experiments were carried out in minimal medium with glucose as the carbon source. In this case, the pHs of the culture of both Pseudomonadaceae strains were almost constant, whereas it suddenly dropped during the exponential growth phase of E. coli. When the initial pH was 6 the extracellular pH fell sharply to 4.5, which irreversibly prevented further cellular growth. Nevertheless, at higher initial pH values subsequent cellular growth of E. coli restored the medium to the initial pHs values. Finally, in all cases the evolution of the pH has been shown to depend on the carbon source used. Among the sources used, cellular growth with glucose or glycerol did not affect the extracellular pH, whereas citrate caused the alkalinization of the media. This phenotype is in concordance with computational predictions, at least in the case of the genome-scale metabolic model of Pseudomonas putida KT2440.

SummaryNitrate signalling on the nitrate reductase (Nia1) gene promoter from Chlamydomonas reinhardtii has been studied by using a construct of the Nia1 promoter transcriptionally fused to the Chlamydomonas arylsulphatase gene as a reporter in strains bearing different sets of nitrate/nitrite transport genes. The high-af®nity nitrate transport (HANT) system I is required for ef®cient signalling by nitrate, even at submicromolar concentrations of the anion. In addition, the autogenous regulation of nitrate reductase has been found to depend on the presence of system I. The low-af®nity nitrate transport system III promoted signalling optimally on the promoter at millimolar nitrate concentrations. The HANT system IV, which is insensitive to ammonium and active at low CO 2 , allowed nitrate signalling at micromolar concentrations even in the presence of ammonium, suggesting that the balance of these two effectors controls Nia1 transcription. Our data indicate that nitrate signalling on the Nia1 gene promoter occurs intracellularly and depends on the activity of nitrate transporters.