Biomedical subjects

Sharon Regan

Publications and source records attributed to Sharon Regan.

5 recordsLinked to original sources

PubMed2005

Potato expressed sequence tag generation and analysis using standard and unique cDNA libraries.

To help develop an understanding of the genes that govern the developmental characteristics of the potato (Solanum tuberosum), as well as the genes associated with responses to specified pathogens and storage conditions, The Canadian Potato Genome Project (CPGP) carried out 5' end sequencing of regular, normalized and full-length cDNA libraries of the Shepody potato cultivar, generating over 66,600 expressed sequence tags (ESTs). Libraries sequenced represented tuber developmental stages, pathogen-challenged tubers, as well as leaf, floral developmental stages, suspension cultured cells and roots. All libraries analysed to date have contributed unique sequences, with the normalized libraries high on the list. In addition, a low molecular weight library has enhanced the 3' ends of our sequence assemblies. Using the combined assembly dataset, unique tuber developmental, cold storage and pathogen-challenged sequences have been identified. A comparison of the ESTs specific to the pathogen-challenged tuber and foliar libraries revealed minimal overlap between these libraries. Mixed assemblies using over 189,000 potato EST sequences from CPGP and The Institute for Genomics Research (TIGR) has revealed common sequences, as well as CPGP- and TIGR-unique sequences.

DNA, Complementary↗

PubMed2003

How plants make tubes.

The plant body requires the transport of various materials over large distances. Two cell types that bear a striking resemblance morphologically are the cells specialized for water transport and those responsible for the transport of oxygen: xylem and lysigenous aerenchyma, respectively. Each of these cell types undergoes programmed cell death and cellular autolysis, resulting in the production of a functional space within the plant body. The major morphological difference observed is the presence of the lignified secondary wall in water-conducting tissues. The prevalence of tubular structures in other plant tissues suggests that the ability to form spaces through cellular autolysis is a fundamental paradigm in plant development and evolution.

Biological Evolution↗

PubMed2003

Asymmetric expression of a poplar ACC oxidase controls ethylene production during gravitational induction of tension wood.

Ethylene is produced in wood-forming tissues, and when applied exogenously, it has been shown to cause profound effects on the pattern and rate of wood development. However, the molecular regulation of ethylene biosynthesis during wood formation is poorly understood. We have characterised an abundant 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase gene (PttACO1) in the wood-forming tissues of Populus tremula (L.) x P. tremuloides (Michx). PttACO1 is primarily expressed in developing secondary xylem, and is specifically upregulated during secondary wall formation. Nevertheless, according to GC-MS analysis combined with tangential cryosectioning, the distribution of ACC was found to be fairly uniform across the cambial-region tissues. Gravitational stimulation, which causes tension wood to form on the upper side of the stem, resulted in a strong induction of PttACO1 expression and ACC oxidase activity in the tension wood-forming tissues. The ACC levels increased in parallel to the PttACO1 expression. However, the increase on the upper (tension wood) side was only minor, whereas large amounts of both ACC and its hydrolysable conjugates accumulated on the lower (opposite) side of the stem. This suggests that the relatively low level of ACC on the tension wood side is a result of its conversion to ethylene by the highly upregulated PttACO1, and the concurrent accumulation of ACC on the opposite side of the wood is because of the low PttACO1 levels. We conclude that PttACO1 and ACC oxidase activity, but not ACC availability, are important in the control of the asymmetric ethylene production within the poplar stem when tension wood is induced by gravitational stimulation.

Amino Acid Oxidoreductases↗

PubMed2002

Secondary xylem development in Arabidopsis: a model for wood formation.

Our understanding of the molecular controls regulating the identity of the vascular cambium and the development of secondary xylem and phloem have not yet benefited much from the use of Arabidopsis as a genetic system. Under appropriate growth conditions Arabidopsis undergoes extensive secondary growth in the hypocotyl, with the development of both a vascular and a cork cambium. The secondary xylem of the hypocotyl develops in two phases, an early phase in which only vessel elements mature and a later stage in which both vessel elements and fibres are found. During this second phase the secondary xylem of Arabidopsis closely resembles the anatomy of the wood of an angiosperm tree, and can be used to address basic questions about wood formation. The development of the vascular cambium and secondary growth in Arabidopsis hypocotyl is described and its utility as a model for wood formation in trees is considered.

Journal Article↗

PubMed2002

Poplar potassium transporters capable of controlling K+ homeostasis and K+-dependent xylogenesis.

The cambial K+ content of poplar increases during the growth period in a K+ supply dependent manner. Upon K+ starvation or application of tetraethylammoniumchloride (TEA+), a K+ channel blocker, the average vessel lumen and expansion zone area were significantly reduced. In search for the molecular basis of potassium-dependent xylogenesis in poplar, K+ transporters homologous to those of known function in Arabidopis phloem- and xylem-physiology were isolated from a poplar wood EST library. The expression profile of three distinct K+ channel types and one K+ transporter, Populus tremula K+ uptake transporter 1 (PtKUP1), was analysed by quantitative RT-PCR. Thereby, we found P. tremula outward rectifying K+ channel (PTORK) and P. tremula K+ channel 2 (PTK2) correlated with the seasonal wood production. K+ transporter P. tremula 1 (KPT1) was predominantly found in guard cells. Following the heterologous expression in Xenopus oocytes the biophysical properties of the different channels were determined. PTORK, upon membrane de-polarization mediates potassium release. PTK2 is almost voltage independent, carrying inward K+ flux at hyperpolarized potential and K+ release upon de-polarization. PtKUP1 was expressed in a K+ uptake-deficient Escherichia coli strain, where this K+ transporter rescued K+-dependent growth. In order to link the different K+ transporters to the cambial activity and wood production, we compared the expression profiles to seasonal changes in the K+ content of the bark as well as xylem vessel diameter. Thereby, we found PTORK and PTK2 transcripts to follow the annual K+ variations in poplar branches. PtKUP1 was expressed at a low level throughout the year, suggesting a housekeeping function. From these data, we conclude that K+ channels are involved in the regulation of K+-dependent wood production.

Animals↗