RESUMO
Jasmonates are well documented for their ability to modulate the expression of plant genes and to influence specific aspects of disease/pest resistance traits. We and others have been studying the synthesis of sesquiterpene phytoalexins in elicitor/pathogen-challenged plants and have sought to determine if methyl jasmonate (MeJA) could substitute for fungal elicitors in the induction of capsidiol accumulation by tobacco cell cultures. The current results demonstrate that MeJA does in fact induce phytoalexin accumulation, but with a much more delayed induction time course than elicitor. While elicitor treatment induced strong but transient changes in key enzymes of sesquiterpene biosynthesis, sesquiterpene cyclase, and aristolochene/deoxy-capsidiol hydroxylase, MeJA did not. Instead, MeJA caused a protracted induction of cyclase activity and only a low level of hydroxylase activity. MeJA induced the expression of at least two sesquiterpene cyclase genes, including one that had not been observed previously in elicitor-induced mRNA populations. Only a small portion of the total sesquiterpene cyclase mRNA induced by MeJA was associated with polysomal RNA, suggesting that the MeJA treatment imposed both transcriptional and posttranscriptional regulation in tobacco cells. These results are not consistent with MeJA playing a role in orchestrating defense responses in elicitor-treated tobacco cells, but do provide evidence that MeJA induces a subset of genes coding for the biosynthesis of sesquiterpene phytoalexins.
Assuntos
Acetatos/farmacologia , Ciclopentanos/farmacologia , Nicotiana/metabolismo , Plantas Tóxicas , Sesquiterpenos/metabolismo , Sequência de Aminoácidos , Sequência de Bases , Carbono-Carbono Liases/genética , Células Cultivadas , Celulase/farmacologia , Primers do DNA/genética , DNA de Plantas/genética , Proteínas Fúngicas/farmacologia , Regulação Enzimológica da Expressão Gênica/efeitos dos fármacos , Regulação da Expressão Gênica de Plantas/efeitos dos fármacos , Genes de Plantas , Dados de Sequência Molecular , Oxilipinas , Reguladores de Crescimento de Plantas/farmacologia , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , RNA de Plantas/genética , RNA de Plantas/metabolismo , Homologia de Sequência de Aminoácidos , Homologia de Sequência do Ácido Nucleico , Nicotiana/efeitos dos fármacos , Nicotiana/genéticaRESUMO
Among other natural products such as colorants and flavorants, natural fungicides like the pepper phytoalexin capsidiol, and the related biochemical pathways, may be used for practical approaches. Key enzymes such as 3-hydroxy-3-methylglutaryl Coenzyme A: reductase, the farnesyl pyrophosphate synthase and and farnesyl pyrophosphate cyclases are known and some related genes have been isolated. However, specific enzymes for important and final modifications as methylation and others, are still to be studied. Construction of chimeric enzymes allowed already the synthesis of different products and the possibilities of designing new enzymes by gene manipulation to produce unknown and useful chemicals are open.
Assuntos
Agricultura/métodos , Capsicum/metabolismo , Plantas Medicinais , Terpenos/metabolismo , Alquil e Aril Transferases/metabolismo , Carbono-Carbono Liases/metabolismo , Geraniltranstransferase , Hidroximetilglutaril-CoA Redutases/metabolismo , Plantas Geneticamente Modificadas , Sesquiterpenos/metabolismoRESUMO
The biosynthesis of the sesquiterpenic phytoalexin capsidiol was investigated using in vitro root cultures of chili pepper (Capsicum annuum) elicited with cellulase. Optimal concentrations of cellulase and sucrose for capsidiol production were established. A simple spectrophotometric procedure to quantify capsidiol was improved. Monoclonal antibodies against a tobacco sesquiterpene cyclase were used to detect a similar protein in pepper root extracts. We found that capsidiol was secreted to the medium and the maximal production was achieved at 24 h after elicitation. In contrast, the maximal amount of the elicitor inducible sesquiterpene cyclase was found between 6 and 8 h. Addition of small amounts of polyvinylpyrrolidone was necessary for sesquiterpene cyclase enzyme activity assays.
