Biomedical subjects

Doil Choi

Publications and source records attributed to Doil Choi.

24 records · Page 2Linked to original sources

PubMed2003

Capsicum annuum dehydrin, an osmotic-stress gene in hot pepper plants.

Osmotic stress-related genes were selected from an EST database constructed from 7 cDNA libraries from different tissues of the hot pepper. A full-length cDNA of Capsicum annuum dehydrin (Cadhn), a late embryogenesis abundant (lea) gene, was selected from the 5' single pass sequenced cDNA clones and sequenced. The deduced polypeptide has 87% identity with potato dehydrin C17, but very little identity with the dehydrin genes of other organisms. It contains a serine-tract (S-segment) and 3 conserved lysine-rich domains (K-segments). Southern blot analysis showed that 2 copies are present in the hot pepper genome. Cadhn was induced by osmotic stress in leaf tissues as well as by the application of abscisic acid. The RNA was most abundant in green fruit. The expression of several osmotic stress-related genes was examined and Cadhn proved to be the most abundantly expressed of these in response to osmotic stress.

Abscisic Acid↗

PubMed2003

Involvement of hydrogen peroxide in repression of catalase in TMV-infected resistant tobacco.

Catalases are ubiquitous, and play a role in plant defense against pathogens. We have reported that catalase mRNA and enzyme activity are repressed in the vicinity of hypersensitive tobacco lesions following TMV infection. We wished to identify the signals involved in this repression. Inoculation with TMV reduced catalase levels 26 to 28 h following infection, coincident with the known timing of endogenous salicylic acid (SA) accumulation. Application of SA caused a transient reduction in Ngcat1 mRNA level and catalase activity 4 to 6 h after treatment. However, repression was also observed in transgenic plants harboring the salicylate hydroxylase gene (NahG) and in TMV susceptible plants, which do not accumulate SA following TMV infection. In the same blots there was no induction of PR-1 or enhanced expression of H2O2-inducible glutathione-S-transferase and found that exposure to H2O2 also repressed Ngcat1 mRNA. Our findings suggest that repression of catalase transcription may be caused by the accumulation of H2O2 rather than of SA.

Catalase↗

PubMed2003

Activation of the programmed cell death pathway by inhibition of proteasome function in plants.

Proteasomes constitute the major machinery to degrade or process proteins by ATP/ubiquitin-mediated proteolysis. Recent findings suggest a pivotal role of the ubiquitin/proteasome pathway in the regulation of apoptosis in animal cells. Here we show that virus-induced gene silencing of two different subunits of the 26 S proteasome, the alpha 6 subunit of the 20 S proteasome and RPN9 subunit of 19 S regulatory complex, both activated the programmed cell death (PCD) program, accompanied by reduced proteasome activity and accumulation of polyubiquitinated proteins. These results demonstrate that disruption of proteasome function leads to PCD in plant cells. The affected cells showed morphological markers of PCD, including nuclear condensation and DNA fragmentation, accompanied by the 10-fold higher production of reactive oxygen species and increased ion leakage for 3-fold. Similar to apoptosis in animal system, mitochondrial membrane potential was decreased, cytochrome c released from mitochondria to cytosol, and caspase 9- and caspase 3-like proteolytic activities detected in the cells. Interestingly, this proteasome-mediated PCD stimulated the expression of only a subset of transcripts that are highly induced during pathogen-mediated hypersensitive response cell death, indicating that the two PCD pathways are differentially regulated. Taken together, these results provide the first direct evidence that proteasomes play a role in the regulatory program of PCD in plants. Controlled inhibition of proteasome activities may be involved in developmentally or environmentally activated plant cell death programs.

Apoptosis↗

PubMed2002

A gene encoding stellacyanin is induced in Capsicum annuum by pathogens, methyl jasmonate, abscisic acid, wounding, drought and salt stress.

A stellacyanin cDNA clone (CASLP1) was isolated from a pepper cDNA library from hypersensitive response (HR) lesions of leaves infected with an avirulent strain of Xanthomonas campestris pv. vesicatoria. The deduced amino acid sequences of CASLP1 are homologous to those of stellacyanins from cucumber, maize, pea and Arabidopsis. The CASLP1 mRNA was not constitutively expressed in all organs of pepper, but strongly induced and accumulated in pepper tissues infected with X. campestris pv. vesicatoria, Colletotrichum coccodes, Phytophthora capsici or C. gloeosporioides. In situ hybridization results revealed that CASLP1 transcripts were strongly localized in the phloem areas of vascular bundles in infected tissues of pepper stems and fruits. CASLP1 mRNA accumulation was found in lower pepper leaves infected by either virulent or avirulent strains of X. campestris pv. vesicatoria and non-pathogenic Pseudomonas fluorescens, but not in uninoculated upper leaves. Induction of this CASLP1 gene occurred in pepper leaves applied with methyl jasmonate (MeJA), but not with ethylene, salicylic acid, dl-beta-amino-n-butyric acid and benzothiadiazole. Accumulation of CASLP1 transcripts was locally or systemically induced in pepper leaves upon mechanical wounding and was activated in a MeJA-dependent manner. The CASLP1 transcript was also strongly induced in leaf and stem tissues after exposure of pepper plants to abscisic acid, salt and drought.

Journal Article↗

PubMed2002

Pathogen-induced expression of cyclo-oxygenase homologue in hot pepper (Capsicum annuum cv. Pukang).

The hypersensitive reaction (HR) in plants is typified by a rapid and localized cell death at the site of pathogen infection. To understand better the molecular and cellular defence mechanism controlling HR, hot pepper leaves (Capsicum annuum cv. Pukang) were inoculated with the soybean pustule pathogen Xanthomonas campestris pv. glycine 8ra. By using the DD-PCR technique, a cDNA fragment was identified that exhibited a sequence similarity to the recently identified tobacco pathogen-induced oxygenase (PIOX) with homology to animal cyclo-oxygenase (COX). Subsequently, the full-length cDNA clone, pCa-COX1, encoding the COX homologue from the pathogen-inoculated hot pepper leaf cDNA library was isolated. The deduced amino acid sequence of Ca-COX1 shares 85.8% identity with tobacco PIOX and displays a significant degree of sequence identity (21.7-23.7%) with mammalian COXs. The expression of Ca-COX1 was markedly induced at 4-12 h after pathogen infection, while HR cell death on pepper leaves appeared at approximately 15 h post-inoculation. These results are consistent with the notion that the lipid-derived signalling pathway is involved in the initial response of hot pepper plants to pathogen infection.

Amino Acid Sequence↗

PubMed2002

PPI1: a novel pathogen-induced basic region-leucine zipper (bZIP) transcription factor from pepper.

We have isolated a full-length cDNA, PPI1 (pepper-PMMV interaction 1), encoding a novel basic region-leucine zipper (bZIP) DNA-binding protein, from expressed sequence tags differentially expressed in Capsicum chinense P1257284 infected with Pepper mild mottle virus (PMMV). PPI1 encodes a predicted protein of 170 amino acids and contains a putative DNA-binding domain that shares significant amino acid identity with ACGT-binding domains of members of the bZIP DNA-binding protein family. PPI1 was localized in the nucleus and had transcriptional activation activity in yeast. Transcripts of the PPI1 gene were preferentially induced during an incompatible interaction by inoculation with PMMV, Pseudomonas syringae pv. syringae 61, and Xanthomonas campestris pv. vesicatoria race 3. However, the PPII gene was not induced by abiotic stressors that activate the plant defense-signaling pathway. Our data provide the first evidence that a bZIP transcription factor is preferentially induced by pathogen attack, suggesting that PPI1 may play a specific functional role in the regulation of expression of plant defense-related genes.

Amino Acid Sequence↗