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Arabidopsis IQD1, a novel calmodulin‐binding nuclear protein, stimulates glucosinolate accumulation and plant defense
Author(s) -
Levy Maggie,
Wang Qiaomei,
Kaspi Roy,
Parrella Michael P.,
Abel Steffen
Publication year - 2005
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1111/j.1365-313x.2005.02435.x
Subject(s) - glucosinolate , biology , arabidopsis , phloem , arabidopsis thaliana , microbiology and biotechnology , plant defense against herbivory , myzus persicae , calmodulin , nuclear localization sequence , mutant , gene , genetics , biochemistry , botany , aphid , enzyme , brassica
Summary Glucosinolates are a class of secondary metabolites with important roles in plant defense and human nutrition. To uncover regulatory mechanisms of glucosinolate production, we screened Arabidopsis thaliana T‐DNA activation‐tagged lines and identified a high‐glucosinolate mutant caused by overexpression of IQD1 ( At3g09710 ). A series of gain‐ and loss‐of‐function IQD1 alleles in different accessions correlates with increased and decreased glucosinolate levels, respectively. IQD1 encodes a novel protein that contains putative nuclear localization signals and several motifs known to mediate calmodulin binding, which are arranged in a plant‐specific segment of 67 amino acids, called the IQ67 domain. We demonstrate that an IQD1‐GFP fusion protein is targeted to the cell nucleus and that recombinant IQD1 binds to calmodulin in a Ca 2+ ‐dependent fashion. Analysis of steady‐state messenger RNA levels of glucosinolate pathway genes indicates that IQD1 affects expression of multiple genes with roles in glucosinolate metabolism. Histochemical analysis of tissue‐specific IQD1 :: GUS expression reveals IQD1 promoter activity mainly in vascular tissues of all organs, consistent with the expression patterns of several glucosinolate‐related genes. Interestingly, overexpression of IQD1 reduces insect herbivory, which we demonstrated in dual‐choice assays with the generalist phloem‐feeding green peach aphid ( Myzus persicae ), and in weight‐gain assays with the cabbage looper ( Trichoplusia ni ), a generalist‐chewing lepidopteran. As IQD1 is induced by mechanical stimuli, we propose IQD1 to be novel nuclear factor that integrates intracellular Ca 2+ signals to fine‐tune glucosinolate accumulation in response to biotic challenge.