Biomedical subjects

C Doering-Saad

Publications and source records attributed to C Doering-Saad.

4 recordsLinked to original sources

PubMed2006

A phloem-enriched cDNA library from Ricinus: insights into phloem function.

The aim of this study was to identify genes that are expressed in the phloem. Increased knowledge of phloem regulation will contribute to our understanding of its many roles, from transport of solutes to information about interactions with pathogens. A cDNA library constructed from phloem-enriched sap exuding from cut Ricinus communis (L.) hypocotyls was sequenced. To assess contamination from other tissues, two libraries were constructed: one using the first 15 min of exudation and the other from sap collected after 120 min of exudation had elapsed. Of 1012 clones sequenced, 158 unique transcripts were identified. The presence of marker molecules such as profilin, the low occurrence of chloroplast-related mRNAs, and the sieve element localization of constituent mRNA using in situ hybridization were consistent with a phloem origin of the sap. Functional analysis of the cDNAs revealed classifications including ribosomal function, interaction with the environment, transport, DNA/RNA binding, and protein turnover. An analysis of the closest Arabidopsis thaliana (L.) homologue for each clone indicated that genes involved in cell localization, protein synthesis, tissue localization, organ localization, organ differentiation, and cell fate were represented at twice the level occurring in the whole Arabidopsis genome. The transcripts found in this phloem-enriched library are discussed in the context of phloem function and the relationship between the companion cell and sieve element.

Amino Acids↗

PubMed2002

Sensitivity of cell hydraulic conductivity to mercury is coincident with symplasmic isolation and expression of plasmalemma aquaporin genes in growing maize roots.

Root elongation occurs as individual cells along the growing zone increase in volume. This increase is caused by water entering the cell either by moving across the cell membrane from the apoplast via aquaporins, or entering through plasmodesmata that symplastically connect cells to each other or with the sieve element. In this investigation we used mercury, a known inhibitor of aquaporin water channels, to manipulate the water permeability of growing maize root cells. 20 micro M HgCl(2) was found to reduce root elongation by around 75% and this reduction in growth was greatest in the older growing cells, with little effect on the younger cells near the root tip. Cell hydraulic conductivity (Lp) of cells close to the root tip (at 3 mm) remained unaffected by mercury treatment in contrast to older growing and non-growing cells where Lp was greatly reduced. Using reverse transcription-polymerase chain reaction analysis, younger root regions were shown to express higher levels of two plasmalemma intrinsic protein genes than older root regions further away from the root tip. However, a gene encoding a tonoplast aquaporin was expressed at similar levels in both regions of the growing zone. The fluorescent tracer, carboxyfluorescein, demonstrated symplastic connection between the phloem and root cortical cells at 3 mm but not at 5 or 20 mm. The data are consistent with a decrease in symplastic continuity along the growing zone and highlight a change in the principal pathway of water uptake during the development of the growing root cell.

Algorithms↗

PubMed1998

Expression cloning of a fungal proline-rich glycoprotein specific to the biotrophic interface formed in the Colletotrichum-bean interaction.

The monoclonal antibody, UB25, recognises a glycoprotein specifically located at the biotrophic interface formed in the Colletotrichum lindemuthianum-bean interaction. The antibody labels the walls of intracellular hyphae and the interfacial matrix which separates them from the invaginated host plasma membrane. In Western blots, UB25 recognises a ladder of bands which are multiples of M(r) 40.5 kDa. A full length cDNA encoding the glycoprotein recognised by UB25 has been isolated by expression cloning and designated CIH1 (Colletotrichum Intracellular Hypha 1). In vitro transcription/translation of CIH1, and transfection of mammalian COS cells, showed that UB25 recognized the expressed product in both procedures confirming that the clones isolated were true positives. Southern analysis of bean and C. lindemuthianum genomic DNA indicated that the CIH1 glycoprotein is fungally encoded and Northern analysis showed that it is only expressed in planta. Analysis of the deduced amino acid sequence of CIH1 indicates the presence of an N-terminal signal sequence and two possible sites for N-glycosylation. The N-terminal domain of the mature protein is rich in proline and contains several short repetitive motifs. CIH1 is thus a fungal proline-rich glycoprotein which appears to form a cross-linked structure in planta and, as such, resembles plant cell wall proline- and hydroxyproline-rich proteins. Possible functions for the CIH1 protein in the establishment and maintenance of biotrophy are discussed.

Amino Acid Sequence↗

PubMed1992

Diversity among Streptomyces Strains Causing Potato Scab.

Eighty Streptomyces isolates, including 35 potato scab-inducing strains and 12 reference strains of Streptomyces scabies, were physiologically characterized by a total of 329 miniaturized tests. Overall similarities of all strains were determined by numerical taxonomy, with the unweighted average linkage (UPGMA) algorithm and simple matching (S(sm)) and Jaccard (S(j)) coefficients used as measures for similarity. Three cluster groups (A to C) were defined at a similarity level of 80.1% (S(sm)); these groups contained 14 clusters and 24 unclustered strains defined at a similarity level of 86.5% (S(sm)). Cluster group A contained strains phenotypically related to S. griseus or S. exfoliatus, whereas cluster group B contained strains which were phenotypically related to S. violaceus or S. rochei. The majority of the pathogenic isolates and reference strains were assigned to S. violaceus (57%) and S. griseus (22%). A DNA probe derived from the rRNA operon of S. coelicolor IMET 40271 was used to detect restriction fragment length polymorphisms (RELPs) among 40 pathogenic and nonpathogenic Streptomyces isolates. Southern blots revealed a high degree of diversity among the pathogenic strains tested. No significant correlation between numerical classification and RFLP grouping of Streptomyces strains could be revealed. The results obtained suggest that RFLP data are of minor importance in classification of Streptomyces species and that genes for pathogenicity determinants are spread among different Streptomyces species by mobilizable elements.

Journal Article↗