Arabidopsis IQD1, a novel calmodulin-binding nuclear protein, stimulates glucosinolate accumulation and plant defense

Maggie Levy, Qiaomei Wang, Roy Kaspi, Michael P. Parrella, Steffen Abel*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

199 Scopus citations

Abstract

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 Ca2+-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 Ca2+ signals to fine-tune glucosinolate accumulation in response to biotic challenge.

Original languageAmerican English
Pages (from-to)79-96
Number of pages18
JournalPlant Journal
Volume43
Issue number1
DOIs
StatePublished - Jul 2005
Externally publishedYes

Keywords

  • Arabidopsis
  • Calmodulin-binding protein
  • Genetic screen
  • Glucosinolates
  • Nuclear localization
  • Secondary metabolism

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