Biomedical subjects

Polydefkis Hatzopoulos

Publications and source records attributed to Polydefkis Hatzopoulos.

8 recordsLinked to original sources

PubMed2006

Oleosin gene expression in olive.

To study the spatial and temporal regulation of oleosin gene expression during olive drupe development, a cDNA (OeOLE) was isolated from embryos. The deduced amino acid sequence of 165 amino acid residues exhibits a long central hydrophobic stretch, including the conserved "proline knot" motif. Phylogenetic analysis grouped OeOLE into the class of high (H) molecular weight oleosins. Southern blotting indicated that the gene is represented by 1-2 copies in the olive genome. Transcript analysis revealed that OeOLE is expressed solely in seeds. A similar bell-shaped pattern of expression was observed in both embryos and endosperms. Transcript accumulation starts at late heart embryo stage, reaches maximum levels at mid-torpedo stage and thereafter declines, coinciding the stages of most oil accumulation in those tissues.

Amino Acid Motifs↗

PubMed2005

Temporal and transient expression of olive enoyl-ACP reductase gene during flower and fruit development.

Enoyl-ACP reductase is a catalytic component of the fatty acid synthetase (FAS) type II system in plants that is involved in the de novo fatty acid biosynthesis in plastids. A cDNA encoding an enoyl-ACP reductase responsible for the removal of the trans-unsaturated double bonds to form saturated acyl-ACP has been isolated from a library made from ripening fruits of Olea europaea L. The predicted protein contains 393 amino acid residues including a consensus chloroplast specific transit peptide. A strong homology was observed when olive enoyl-ACP reductase aligned with other plant sequences. Southern hybridization analysis revealed that enoyl-ACP reductase is encoded by a single gene in olives. Northern hybridization showed a transient expression of the enoyl-ACP reductase (ENR) gene at early stages of drupe (5-7 weeks after flowering, WAF), embryo and endosperm (13-16 WAF) while in mesocarp (13-19 WAF) the expression remained at high levels. In situ hybridization showed particularly prominent expression in the palisade and vascular tissue of young leaves, the tapetum, developing pollen grains and vascular tissue of anthers and to less extent in the embryo sac and transmitting tissue of the carpel. The distinctive spatial and temporal regulation of the ENR gene is consistent with major roles, not only in thylakoid membrane formation and fatty acid deposition, but also in the provision of precursor molecules for the biosynthesis of oxilipins that are important in plant tissues involved in transportation and reproduction.

Amino Acid Sequence↗

PubMed2004

AFLP reveals structural details of genetic diversity within cultivated olive germplasm from the Eastern Mediterranean.

Amplified fragment length polymorphism (AFLP) analysis was used to assess genetic inter-relationships among olive varieties cultivated in the Eastern Mediterranean Basin. The genotypes sampled included most of the important cultivars from Turkey, Greece and the Middle East and selected genotypes from the Western Mediterranean area. A total of 119 polymorphic markers were generated from five selective primer-pair combinations. The combined data sets generated by just two primer-pairs were adequate to discriminate between all 65 genotypes, while each primer-pair could individually identify up to 64 genotypes. A factorial correspondence analysis (FCA) plot indicated that the cultivars clustered into two relatively modestly defined groups. The first broad group was dominated by cultivars from Turkey but also included genotypes originating from the Middle East (Syria and Lebanon) that collectively formed a tight subcluster. The second group comprised Greek cultivars and those originating from the Western Mediterranean. A significant genetic distance value between Greek and Turkish cultivars was provided by an analysis of molecular variance (AMOVA). There was also evidence of substructure here, with an apparent separation of most Spanish and Italian clones. These findings are in general accordance to previous suggestions of an East-West divergence of olive cultivars, although the dichotomy is less extensive than reported previously and complicated by regional variation within each group.

Analysis of Variance↗

PubMed2004

Tight regulation of expression of two Arabidopsis cytosolic Hsp90 genes during embryo development.

The spatial and temporal distribution of expression of two cytosolic members of the AtHsp90 gene family was assessed during early development. In stressed transgenic plants bearing the AtHsp90-3 promoter, beta-glucuronidase (GUS) activity was strong in meristematic tissues. Expression was also detected in vascular tissues, leaf veins, siliques, and in pollen sacs. The promoter induced gene expression after heat shock in a time-course dependent manner. AtHsp90-1 promoter activity was low throughout the early stages of embryo development but high just before embryo maturation, with expression most prominent in cotyledons. AtHsp90-3 promoter activity was almost constant and restricted to the root and the cotyledon tips of the embryo. This highly specific spatial distribution of GUS activity changed when the tissues were heat-stressed. Both promoters were also active in unstressed mature pollen grains and during pollen germination. The results shown here indicate that different regulatory and developmental mechanisms control and differentiate the expression of the two cytosolic members of the Arabidopsis AtHsp90 gene family under normal conditions. The developmental and restricted pattern of expression of the AtHsp90-1 and -3 gene promoters in unstressed transgenic plants suggest prominent and distinctive roles of these two genes during different developmental processes.

Arabidopsis↗

PubMed2004

Potassium carrier TRH1 is required for auxin transport in Arabidopsis roots.

Disruption of the TRH1 potassium transporter impairs root hair development in Arabidopsis, and also affects root gravitropic behaviour. Rescue of these morphological defects by exogenous auxin indicates a link between TRH1 activity and auxin transport. In agreement with this hypothesis, the rate of auxin translocation from shoots to roots and efflux of [3H]IAA in isolated root segments were reduced in the trh1 mutant, but efflux of radiolabelled auxin was accelerated in yeast cells transformed with the TRH1 gene. In roots, Pro(TRH1):GUS expression was localized to the root cap cells which are known to be the sites of gravity perception and are central for the redistribution of auxin fluxes. Consistent with these findings, auxin-dependent DR5:GUS promoter-reporter construct was misexpressed in the trh1 mutant indicating that partial block of auxin transport through the root cap is associated with upstream accumulation of the phytohormone in protoxylem cells. When [K+] in the medium was reduced from 20 to 0.1 mm, wild type roots showed mild agravitropic phenotype and DR5:GUS misexpression in stelar cells. This pattern of response to low external [K+] was also affected by trh1 mutation. We conclude that the TRH1 carrier is an important part of auxin transport system in Arabidopsis roots.

Arabidopsis↗

PubMed2003

AKT1 and TRH1 are required during root hair elongation in Arabidopsis.

TRH1 is a member of the AtKT/AtKUP/AtHAK family of potassium carriers that is required for root hair elongation and AKT1 is an inward rectifying potassium channel expressed in the root epidermis, endodermis and cortex of Arabidopsis thaliana. Plants homozygous for the trh1-1 mutation form short root hairs. The Trh1(-) phenotype cannot be suppressed by growing plants homozygous for the trh1-1 mutation in the presence of high external KCl concentration. This indicates an absolute requirement for TRH1 in root hair tip growth. Plants homozygous for the akt1-1 mutation develop longer root hairs than the wild type when grown in 0 mM external potassium, but develop shorter hairs than the wild type when grown in higher concentrations [>10 mM] of potassium. These data indicate that both TRH1 and AKT1 are active in the root hair over a wide range of external potassium concentrations, but suggest they have different functions in the growing hair cell.

Arabidopsis↗

PubMed2003

Genetic diversity among accessions of an ancient olive variety of Cyprus.

To evaluate germplasm variability and to discriminate between accessions of 'Ladolia', an ancient olive variety of Cyprus, different accessions from a germplasm collection were screened with 11 selected oligonucleotide primers in RAPD-PCRs. A total of 49 polymorphic markers were scored, the combination of which resulted in 70 distinct electrophoretic patterns. Based on either unique or combined patterns, all accessions were identified. Seven genotype-specific markers were detected. One RAPD marker could distinguish accessions according to fruit size. Genetic similarities between accessions, estimated using the Dice similarity coefficient, indicated a high degree of genetic diversity among 'Ladolia' accessions. Genetic relationships were estimated by the unweighted pair-group method with arithmetic averaging (UPGMA) and principal components analysis (PCA). Three main groups of accessions were detected. The first group was generally composed of accessions with small-sized fruits and could be further divided into two subgroups. According to PCA, most accessions with medium- or large-sized fruits were clustered together. Our results support previous observations suggesting that 'Ladolia' is actually a highly variable mixture of genetically distinct landraces.

Cluster Analysis↗

PubMed2002

Combinatorial interaction of cis elements specifies the expression of the Arabidopsis AtHsp90-1 gene.

The promoter region of the Arabidopsis AtHsp90-1 gene is congested with heat shock elements and stress response elements, as well as with other potential transcriptional binding sites (activating protein 1, CCAAT/enhancer-binding protein element, and metal regulatory element). To determine how the expression of this bona fide AtHsp90-1 gene is regulated, a comprehensive quantitative and qualitative promoter deletion analysis was conducted under various environmental conditions and during development. The promoter induces gene expression at high levels after heat shock and arsenite treatment. However, our results show that the two stress responses may involve common but not necessarily the same regulatory elements. Whereas for heat induction, heat shock elements and stress response elements act cooperatively to promote high levels of gene expression, arsenite induction seems to require the involvement of activating protein 1 regulatory sequences. In stressed transgenic plants harboring the full-length promoter, beta-glucuronidase activity was prominent in all tissues. Nevertheless, progressive deletion of the promoter decreases the level of expression under heat shock and restricts it predominantly in the two meristems of the plant. In contrast, under arsenite induction, proximal sequences induce AtHsp90-1 gene expression only in the shoot meristem. Distally located elements negatively regulate AtHsp90-1 gene expression under unstressed conditions, whereas flower-specific regulated expression in mature pollen grains suggests the prominent role of the AtHsp90-1 in pollen development. The results show that the regulation of developmental expression, suppression, or stress induction is mainly due to combinatorial contribution of the cis elements in the promoter region of the AtHsp90-1 gene.

Acclimatization↗