RESUMO
Mobilization of seed storage reserves is essential for seed germination and seedling establishment. Here, we report that AtDSEL, an Arabidopsis thalianaDAD1-like Seedling Establishment-related Lipase, is involved in the mobilization of storage oils for early seedling establishment. AtDSEL is a cytosolic member of the DAD1-like acylhydrolase family encoded by At4g18550. Bacterially expressed AtDSEL preferentially hydrolyzed 1,3-diacylglycerol and 1-monoacylglycerol, suggesting that AtDSEL is an sn-1-specific lipase. AtDSEL-overexpressing transgenic Arabidopsis plants (35S:AtDSEL) were defective in post-germinative seedling growth in medium without an exogenous carbon source. This phenotype was rescued by the addition of sucrose to the growth medium. In contrast, loss-of-function mutant plants (atdsel-1 and atdsel-2) had a mildly fast-growing phenotype regardless of the presence of an exogenous carbon source. Electron microscopy revealed that 5-day-old 35S:AtDSEL cotyledons retained numerous peroxisomes and oil bodies, which were exhausted in wild-type and mutant cotyledons. The impaired seedling establishment of 35S:AtDSEL was not rescued by the addition of an exogenous fatty acid source, and 35S:AtDSEL seedling growth was insensitive to 2,4-dichlorophenoxybutyric acid, indicating that ß-oxidation was blocked in AtDSEL-overexpressers. These results suggest that AtDSEL is involved in the negative regulation of seedling establishment by inhibiting the breakdown of storage oils.
Assuntos
Ácido 2,4-Diclorofenoxiacético/análogos & derivados , Proteínas de Arabidopsis/metabolismo , Arabidopsis/enzimologia , Lipase/metabolismo , Óleos de Plantas/metabolismo , Plântula/enzimologia , Ácido 2,4-Diclorofenoxiacético/farmacologia , Arabidopsis/genética , Arabidopsis/crescimento & desenvolvimento , Arabidopsis/ultraestrutura , Proteínas de Arabidopsis/genética , Cotilédone/genética , Cotilédone/crescimento & desenvolvimento , Cotilédone/ultraestrutura , Flores/enzimologia , Flores/genética , Expressão Gênica , Germinação , Lipase/genética , Mutação , Organelas/enzimologia , Organelas/metabolismo , Organelas/ultraestrutura , Oxirredução , Fenótipo , Fosfolipases A1/genética , Folhas de Planta/enzimologia , Folhas de Planta/genética , Raízes de Plantas/enzimologia , Raízes de Plantas/genética , Raízes de Plantas/crescimento & desenvolvimento , Caules de Planta/enzimologia , Caules de Planta/genética , Caules de Planta/crescimento & desenvolvimento , Plantas Geneticamente Modificadas , Proteínas Recombinantes de Fusão/genética , Proteínas Recombinantes de Fusão/metabolismo , Plântula/genética , Plântula/crescimento & desenvolvimento , Plântula/ultraestrutura , Sementes/crescimento & desenvolvimento , Sementes/metabolismoRESUMO
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.