Variations in plant metallothioneins: the heavy metal hyperaccumulator <Emphasis Type="Italic">Thlaspi caerulescens</Emphasis> as a study case

Plant metallothioneins (MTs) are extremely diverse and are thought to be involved in metal homeostasis or detoxification. Thlaspi caerulescens is a model Zn/Cd hyperaccumulator and thus constitutes an ideal system to study the variability of these MTs. Two T. caerulescens cDNAs (accession: 665511; accession: 665515), that are highly homologous to type 1 and type 2 Arabidopsis thaliana MTs, have been isolated using a functional screen for plant cDNAs that confer Cd tolerance to yeast. However, TcMT1 has a much shorter N-terminal domain than that of A. thaliana and so lacks Cys motifs conserved through all the plant MTs classified as type 1. A systematic search in plant databases allowed the detection of MT-related sequences. Sixty-four percent fulfil the criteria for MT classification described in Cobbett and Goldsbrough (2002) and further extend our knowledge about other conserved residues that might play an important role in plant MT structure. In addition, 34% of the total MT-related sequences cannot be classified strictly as they display modifications in the conserved residues according to the current plant MTs’ classification. The significance of this variability in plant MT sequences is discussed. Functional complementation in yeast was used to assess whether these variations may alter the MTs’ function in T. caerulescens. Regulation of the expression of MTs in T. caerulescens was also investigated. TcMT1 and TcMT2 display higher expression in T. caerulescens than in A. thaliana. Moreover, their differential expression patterns in organs and in response to metal exposure, suggest that the two types of MTs may have diverse roles and functions in T. caerulescens.     

Comparative genomics in hemiascomycete yeasts: evolution of sex, silencing, and subtelomeres

The recent release of sequences of several unexplored yeast species that cover an evolutionary range comparable to the entire phylum of chordates offers us a unique opportunity to investigate how genes involved in adaptation have been shaped by evolution. We have examined how three different sets of genes, all related to adaptative processes at the genomic level, have evolved in hemiascomycetes: (1) the mating-type genes that govern sexuality, (2) the silencing genes that are connected to regulation of mating-type cassettes and to telomere position effect, and (3) the gene families found repeated in subtelomeric regions.We report new combinations of mating-type genes and cassettes in hemiascomycetous species; we show that silencing proteins diverge rapidly. We have also found that in all species studied, subtelomeric gene families exist and are specific to each species.     

Comparative genomics of hemiascomycete yeasts: genes involved in DNA replication, repair, and recombination

Among genes conserved from bacteria to mammals are those involved in replicating and repairing DNA. Following the complete sequencing of four hemiascomycetous yeast species during the course of the Genolevures 2 project, we have studied the conservation of 106 genes involved in replication, repair, and recombination in Candida glabrata, Kluyveromyces lactis, Debaryomyces hansenii, and Yarrowia lipolytica and compared them with their Saccharomyces cerevisiae orthologues. We found that proteins belonging to the replication fork and to the nucleotide excision repair pathway were-on the average-more conserved than proteins involved in the checkpoint response to DNA damage or in meiotic recombination. The meiotic recombination proteins Spo11p and Mre11p-Rad50p, involved in making meiotic double-strand breaks (DSBs), are conserved as is Mus81p, involved in resolving meiotic recombination intermediates. Interestingly, genes found in organisms in which DSB-repair is required for proper synapsis during meiosis are also found in C. glabrata, K. lactis, and D. hansenii but not in Y. lipolytica, suggesting that two modes of meiotic recombination have been selected during evolution of the hemiascomycetous yeasts. In addition, we found that SGS1 and TOP1, respectively, a DEAD/DEAH helicase and a type I topoisomerase, are duplicated in C. glabrata and that SRS2, a helicase involved in homologous recombination, is tandemly duplicated in K. lactis. Phylogenetic analyses show that the duplicated SGS1 gene evolved faster than the original gene, probably leading to a specialization of function of the duplicated copy.     

The effect of prolonged cold storage of eland (Taurotragus oryx) cauda epididymides on the spermatozoa: possible implications for the conservation of biodiversity

The objectives of this study were to investigate the effects of prolonged storage of cauda epididymides at 4 degrees C on spermatozoa, and to determine the practicality of utilising epididymal sperm, harvested from testes collected during routine culling of game animals, in assisted reproductive technologies. Testes from eland (Taurotragus oryx) were collected and epididymides removed and maintained at 4 degrees C. Sperm motility, viability, morphology and membrane integrity were examined at 12 h intervals for 108 h. Sperm motility and viability were significantly lower at the end of the experiment than at the start (P < 0.05) and there was individual variation in the rate at which motility and viability declined. The total number of normal sperm decreased significantly with prolonged storage at 4 degrees C. Midpiece defects were the most common and head and tail abnormalities were rare. A significant decrease in acrosomal and nuclear membrane integrity was observed with prolonged cold storage but there was no significant change in cell membrane integrity. However, about 30% of epididymal sperm survived for 3 days at 4 degrees C and more than 10% survived for 4 days, and it should be possible to use sperm from culled animals in some assisted reproductive technologies.     

Genetic diversity of Cylindrospermopsis strains (cyanobacteria) isolated from four continents

The genetic diversity of Cylindrospermopsis strains (cyanobacteria) was examined using mainly the 16S-23S internally transcribed spacer (ITS1) sequences. Strains were grouped in three clusters: (i) America, (ii) Europe, and (iii) Africa and Australia. These results suggested a recent spread of Cylindrospermopsis across the American and European continents from restricted warm refuge areas instead of exchanges between continents. On the other hand, they also suggested a recent colonization of Australia by African strains.     

Phylogenetic and morphological re-evaluation of the Botryosphaeria species causing diseases of Mangifera indica

Species of Botryosphaeria are among the most serious pathogens that affect mango trees and fruit. Several species occur on mangoes, and these are identified mainly on the morphology of the anamorphs. Common taxa include Dothiorella dominicana, D. mangiferae (= Natrassia mangiferae), D. aromatica and an unidentified species, Dothiorella 'long'. The genus name Dothiorella, however, is acknowledged as a synonym of Diplodia. This study aimed to characterize and name the Botryosphaeria spp. associated with disease symptoms on mangoes. To achieve this isolates representing all four Dothiorella spp. mentioned above were compared with the anamorphs of known Botryosphaeria spp., based on conidial morphology and DNA sequence data. Two genomic regions were analyzed, namely the ITS rDNA and beta-tubulin regions. The morphological and molecular results confirmed that the fungi previously identified from mango as species of Dothiorella belong to Fusicoccum. Dothiorella dominicana isolates were identical to isolates of F. parvum (teleomorph = B. parva). A new epithet, namely F. mangiferum, is proposed for isolates previously treated as D. mangiferae or N. mangiferae. Isolates of D. aromatica were identified as F. aesculi (teleomorph = B. dothidea). A fourth Fusicoccum sp. also was identified as those isolates previously known as Dothiorella 'long'. A key is provided to distinguish these species based on anamorph morphology in culture. This study provides a basis for the identification of Botryosphaeria species from mango, which is important for disease control and to uphold quarantine regulations.     

Two cyclopeptides from the seeds of Annona cherimola

Bioassay-guided fractionation of cytotoxic of methanol extract of the seeds of Annona cherimola provided two novel cyclic peptides, cherimolacyclopeptide E (1) and cherimolacyclopeptide F (2), which exhibited significant cytotoxic activity against the KB (human nasopharyngeal carcinoma) cell culture system. The peptide 1 and 2 were elucidated by MS/MS fragmentation experiments using a Q-TOF mass spectrometer equipped with an ESI source, extensive 2D NMR analyses and chemical degradation.     

Polar acyclic diterpenoids from Bifurcaria bifurcata (Fucales, Phaeophyta)

From the lipophilic extract of the brown alga Bifurcaria bifurcata collected off the Atlantic coast of Southern Brittany (Quiberon, France), five polar linear diterpenoids have been isolated. These metabolites have been identified as hydroxylated derivatives of 13-oxo- and 13-hydroxygeranylgeraniol. Their structures were characterized on the basis of chemical and spectral evidence including two-dimensional NMR experiments and mass spectrometric techniques. The absolute configuration of the 13-position has been determined, for the 13-hydroxygeranylgeraniol derivatives, to be R by means of a modified Mosher's method and therefore that of 13-hydroxygeranylgeraniol (eleganediol) has been revised. Along with these compounds, three related known geranylgeraniol derivatives were also identified, and these data were used for chemotaxonomical purposes.     

Cherimolacyclopeptide D, a novel cycloheptapeptide from the seeds of Annona cherimola

In a chemical investigation of the seeds of Annona cherimola, a natural cyclic heptapeptide, cherimolacyclopeptide D, were isolated and purified by HPLC with three known cyclic peptides, cherimolacyclopeptides A, B and C. The structure was established by various analyses including MS/MS fragmentation, spectroscopic and chemical evidences.