The life cycle of the amoeboid alga Synchroma grande (Synchromophyceae, Heterokontophyta)--highly adapted yet equally equipped for rapid diversification in benthic habitats.

Synchroma grande (Synchromophyceae, Heterokontophyta) is a marine amoeboid alga, which was isolated from a benthic habitat. This species has sessile cell stages (amoeboid cells with lorica and cysts) and non-sessile cell stages (migrating and floating amoebae) during its life cycle. The different cell types and their transitions within the life cycle are described, as are their putative functions. Cell proliferation was observed only in cells attached to the substrate but not in free-floating or migrating cells. We also characterised the phagotrophy of the meroplasmodium in comparison to other amoeboid algae and the formation of the lorica. The functional adaptations of S. grande during its life cycle were compared to the cell stages of other amoeboid algae of the red and green chloroplast lineages. S. grande was found to be highly adapted to the benthic habitat. One sexual and two asexual reproductive strategies (haplo-diploid life cycle) support the ability of this species to achieve rapid diversification and high adaptivity in its natural habitat.

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Promoter and leader sequences of the spinach PsaD and PsaF genes direct an opposite light response in tobacco cotyledons: PsaD sequences downstream of the ATG codon are required for a positive light response.

Subunits II and III of the photosystem I reaction centre are encoded by the nuclear genes PsaD and PsaF, respectively. In spinach, the expression of both genes is highly synchronized with regard to time, space and in response to stimulators such as light. Nevertheless, promoter sequences as well as the design and location of regulatory elements are strikingly different. Promoter and leader of PsaF, when fused to the GUS reporter gene, direct a positive light response in the cotyledons of transgenic tobacco seedlings. In contrast, the equivalent PsaD regions confer a negative-light regulation to the GUS gene. If a 6-kb fragment that contains 1802 bp of the promoter, the transcription unit as well as additional 2.5 kb downstream of the PsaD gene is introduced into tobacco, the transcript level from the PsaD transgene is positively light-regulated in tobacco cotyledons. Thus, regulatory elements of the spinach PsaD and PsaF promoters are arranged in a very different way and essential cis-determinants for the positive light response of the PsaD gene can be located within the coding region and/or even further downstream.

Promoters from genes for plastid proteins possess regions with different sensitivities toward red and blue light.

The light-regulated expression of eight nuclear-encoded genes for plastid proteins from spinach (Spinacia oleracea) (RBCS-1 and CAB-1; ATPC and ATPD, encoding the subunits gamma and delta of the ATP synthase; PC and FNR; PSAD and PSAF, encoding the subunits II and III of photosystem I reaction center) was analyzed with promoter/beta-glucuronidase (GUS) gene fusions in transgenic tobacco (Nicotiana tabacum and Nicotiana plumbaginifolia) seedlings and mature plants under standardized light and growth conditions. Unique response patterns were found for each of these promoters. GUS activities differed more than 30-fold. Strong promoters were found for the PC and PSAD genes. On the other hand, the ATPC promoter was relatively weak. Expression of the CAB/GUS gene fusion in etiolated material was at the detection limit; all other chimeric genes were expressed in the dark as well. Light stimulation of GUS activities ranged from 3- (FNR promoter) to more than 100-fold (CAB-1 promoter). The FNR promoter responded only to red light (RL) and not significantly to blue light (BL), whereas the PC promoter contained regions with different sensitivities toward RL and BL. Furthermore, different RNA accumulation kinetics were observed for the PSAF, CAB, FNR, and PC promoter/GUS gene fusions during de-etiolation, which, at least in the case of the PSAF gene, differed from the regulation of the corresponding endogenous genes in spinach and tobacco. The results suggest either that not all cis elements determining light-regulated and quantitative expression are present on the spinach promoter fragments used or that the spinach cis-regulatory elements respond differently to the host (tobacco) regulatory pathway(s). Furthermore, as in tobacco, but not in spinach, the trans-gene hardly responds to single light pulses that operate through phytochrome. Taken together, the results suggest that the genes have been independently translocated from the organelle to the nucleus during phylogeny. Furthermore, each gene seems to have acquired a unique set of regulatory elements.

A 42 bp promoter fragment of the gene for subunit III of photosystem I (psaF) is crucial for its activity.

The promoter of the gene for the subunit III of photosystem I reaction center (psaF) from spinach has been dissected and studied via promoter/GUS gene fusions in transgenic tobacco. It possesses an architecture that differs from any other spinach promoter of genes encoding proteins involved in photosynthesis studied to date. A 42 bp region located between -220 and -179 bp upstream of the transcription start site has been identified that is indispensable for expression and binds a trans-acting factor. Maximal light-response is obtained with a -220/+ 163 bp segment, whereas longer promoter sequences are significantly less effective, indicating the existence of upstream elements with silencer characteristics. F1 seedlings show different spatial expression patterns in darkness or light. Etiolated seedlings display high GUS activity in the upper hypocotyl, the hook region and the vascular tissue of the cotyledons, whereas in light-grown seedlings no activity was detected in the hypocotyl and almost all cells of the cotyledons express the GUS gene.

Isolation and characterization of cDNA clones encoding a 18.8 kDa polypeptide, the product of the gene psaL, associated with photosystem I reaction center from spinach.

Several cDNA clones encoding subunit XI of photosystem I reaction center (PSI-L) have been isolated from two lambda gt11 expression libraries based on polyadenylated RNA of spinach seedlings illuminated for 4 and 16 h, respectively. The precursor polypeptide made from these recombinant DNAs in vitro can be efficiently imported into isolated spinach chloroplasts. It is correctly processed to the size of the authentic polypeptide and integrates into the photosystem I assembly. The 834 nucleotide sequence of the longest cDNA insert encodes a precursor polypeptide of 24 kDa (216 residues) and a mature protein of probably 18.8 kDa (169 residues). Hydropathy analysis suggests that the polypeptide contains two transmembrane segments. The protein appears to originate in a single-copy gene in spinach and to be decoded from RNA species of ca. 900 bases.

A plant mitochondrial gene encodes a protein involved in cytochrome c biogenesis.

Analysis of a transcribed region in the mitochondrial genome of Oenothera revealed an open reading frame (ORF) of 577 codons (orf577) that is also conserved in carrot, here encoding a protein of 579 amino acids (orf579). RNA editing alters the mRNA sequence of orf577 in Oenothera with 46 C to U transitions, many of which improve sequence similarity with the homologous Marchantia gene orf509. The deduced polypeptides show significant similarity with the ccl1-encoded protein involved in cytochrome c biogenesis in the photosynthetic bacterium Rhodobacter capsulatus. A highly conserved domain is also found in plastid ORFs, suggesting that these bacterial, chloroplast and mitochondrial genes encode polypeptides with analogous functions in assembly and maturation of cytochromes c.