Regulation of Arabidopsis SHY2/IAA3 protein turnover

• Published in: The Plant journal : for cell and molecular biology 2003-12, Vol.36 (5), p.643-651
• Main Authors: Tian, Qing, Nagpal, Punita, Reed, Jason W.
• Format: Article
• Language: English
• Subjects: Arabidopsis - genetics; Arabidopsis - metabolism; Arabidopsis Proteins - genetics; Arabidopsis Proteins - metabolism; Arabidopsis thaliana; Aux; auxin; Base Sequence; Biological and medical sciences; Cloning, Molecular; DNA Primers; Escherichia coli - genetics; Fundamental and applied biological sciences. Psychology; Gene Expression Regulation, Plant - genetics; IAA proteins; IAA3; IAA3 protein; juglone; Kinetics; Metabolism; Nitrogen metabolism; Nuclear Proteins - genetics; Nuclear Proteins - metabolism; Phytochromes; Plant physiology and development; Polymerase Chain Reaction; Recombinant Proteins - metabolism; SHY2; SHY2 protein; TIR1 protein; turnover
• ISSN: 0960-7412; 1365-313X
• DOI: 10.1046/j.1365-313X.2003.01909.x

Summary Auxin/indole acetic acid (Aux/IAA) proteins regulate transcriptional responses to the plant hormone auxin. Gain‐of‐function mutations in the Arabidopsis SHORT HYPOCOTYL 2 (SHY2/IAA3) gene encoding an Aux/IAA protein increase steady‐state levels of SHY2/IAA3 protein and decrease auxin responses, indicating that SHY2/IAA3 negatively regulates auxin signaling. These shy2 mutations also cause ectopic light responses, suggesting that SHY2/IAA3 may promote light signaling. Auxin regulates turnover of the related Auxin‐resistant (AXR)2/IAA7 and AXR3/IAA17 proteins by increasing their interaction with the Skp1‐Cdc53/cullin‐F‐box (SCFTIR1) E3 ubiquitin ligase complex. To investigate whether SHY2/IAA3 is regulated similarly, we have used a turnover assay to reveal that axr1 and transport inhibitor resistant (tir)1 mutations affecting SCFTIR1 decrease SHY2/IAA3 turnover. In pull‐down assays, SHY2/IAA3 protein interacted with TIR1, the F‐box component of SCFTIR1 and with the photoreceptor phytochrome B. Auxin stimulated SHY2/IAA3 interaction with TIR1, whereas the shy2‐2 gain‐of‐function mutation decreased this interaction. Light did not affect the interaction, suggesting that light regulates some other aspect of Aux/IAA gene or protein function. The chemical juglone (5‐hydroxy‐1,4‐naphthoquinone) inhibited the interaction, suggesting that peptidyl‐prolyl isomerization may mediate auxin‐induced SHY2/IAA3 protein turnover.