Arabidopsis IQD1, a novel calmodulin-binding nuclear protein, stimulates glucosinolate accumulation and plant defense.
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.
Levy
Maggie
M
Department of Plant Sciences, University of California-Davis, One Shields Avenue, Davis, CA 95616, USA.
Wang
Qiaomei
Q
Kaspi
Roy
R
Parrella
Michael P
MP
Abel
Steffen
S
D000595:Amino Acid Sequence; D000818:Animals; D001042:Aphids; D017360:Arabidopsis / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000502:physiology*; D020013:Calcium Signaling; D002147:Calmodulin / Q000378:metabolism; D002148:Calmodulin-Binding Proteins / Q000502:physiology*; D005247:Feeding Behavior; D018506:Gene Expression Regulation, Plant; D005961:Glucosinolates / Q000096:biosynthesis*; D008969:Molecular Sequence Data; D011485:Protein Binding; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D014018:Tissue Distribution
D029681:Arabidopsis Proteins; D002147:Calmodulin; D002148:Calmodulin-Binding Proteins; D005961:Glucosinolates; C503424:IQD1 protein, Arabidopsis