Cloning and Characterization of Potato Tuber Lipoxygenase cDNAs and Studies of Lipoxygenase Expression in Potato and Tomato Plants

AUTOR(ES)
FONTE

IBICT - Instituto Brasileiro de Informação em Ciência e Tecnologia

DATA DE PUBLICAÇÃO

1997

RESUMO

Oxylipins are oxygenated fatty acids that are generated by plants in different contexts, and are often produced in plant tissues following imposition of external stresses such as insect wounding or pathogen infection. Injury and infection result in the release of the polyunsaturated fattty acid substrates and the enzymatic capacity for oxylipin synthesis. The initial step in the generation of certain oxylipins is catalyzed by the lipoxygenase (LOX) reaction. The resulting fatty acid hydroperoxides can elicit, directly or indirectly after further metabolism, different sets of plant responses depending on the particular oxylipins produced. As part of a program to assess LOX function in plant interactions with different pathogens and insects, a potato tuber cDNA library was screened and two lipoxygenase (LOX) clones were isolated and characterized. Both clones, plox1 and plox2, are nearly identical and encode full-length potato tuber LOX sequences that present high homology with other cloned LOXs. The deduced amino acid sequence of plox1 contains iron-binding domains that are conserved among LOXs. plox1 was used as a probe to analyze LOX gene expression at the levels of mRNA abundance in potato and tomato challenged with a variety of agents. The abundance of mRNAs for a wound-inducible proteinase inhibitor (P1NII) and a pathogenesis-related protein (P4) also were determined since these proteins are induced in tomato leaves characteristically following attack by certain insects or pathogenic agents, respectively. In addition, LOX enzyme activity was measured in certain experiments. Expression studies of LOX, PINII, and P4 indicate that their induction does not follow a strict pattern based on the type of biologic inducer (insect vs. pathogen) or chemical treatment, with each specific treatment inducing a distinct pattern of gene expression. The results do not support the hypothesis for a strict dichotomy of signaling by insects and pathogens of LOX, PINII and P4 in tomato. Suppression of host resistance to insects may occur via salicylate-mediated mechanisms, and a pathogen capable of triggering both pathways can significantly enhance resistance to insects.

ASSUNTO(S)

tomato fitossanidade potato lipoxygenase oxylipins plant - pathogen interactions

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