Mutation in domain II of IAA1 confers diverse auxin-related phenotypes and represses auxin-activated expression of Aux/IAA genes in steroid regulator-inducible system.
Most of Aux/IAA genes are rapidly induced by auxin. The Aux/IAA proteins are short-lived nuclear proteins sharing the four conserved domains. Domain II is critical for rapid degradation of Aux/IAA proteins. Among these gene family members, IAA1 is one of the earliest auxin-inducible genes. We used a steroid hormone-inducible system to reveal putative roles and downstream signaling of IAA1 in auxin response. Arabidopsis transgenic plants were generated expressing fusion protein of IAA1 (IAA1-GR) or IAA1 with a mutation in domain II (iaa1-GR) and the glucocorticoid hormone-binding domain (GR). IAA1-GR transgenic plants did not exhibit any discernable phenotypic differences by DEX treatment that allows nuclear translocation of the fusion protein. In contrast, diverse auxin-related physiological processes including gravitropism and phototropism were impaired by DEX treatment in roots, hypocotyls, stems, and leaves in iaa1-GR transgenic plants. Auxin induction of seven Aux/IAA mRNAs including IAA1 itself was repressed by DEX treatment, suggesting that IAA1 functions in the nucleus by mediating auxin response and might act as a negative feedback regulator for the expression of Aux/IAA genes including IAA1 itself. Auxin induction of Aux/IAA genes in the presence of cycloheximide can be repressed by DEX treatment, showing that the repression of transcription of the Aux/IAAs by the iaa1 mutant protein is primary. Wild-type IAA1-GR could not suppress auxin induction of IAA1 and IAA2. These results indicate that inhibition of auxin-activated transcription of Aux/IAA genes by the iaa1 mutant protein might be responsible for alteration of various auxin responses.
Park
Jin-Young
JY
Kumho Life and Environmental Science Laboratory, 1 Oryong-dong, Puk-Gu, Gwangju, Korea 500-712.
Kim
Hye-Joung
HJ
Kim
Jungmook
J
D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism*; D029681:Arabidopsis Proteins; D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D003907:Dexamethasone / Q000494:pharmacology*; D018506:Gene Expression Regulation, Plant / Q000187:drug effects*; D018522:Gravitropism / Q000187:drug effects; D018546:Hypocotyl / Q000187:drug effects / Q000254:growth & development; D007210:Indoleacetic Acids / Q000494:pharmacology*; D009154:Mutation / Q000235:genetics*; D009687:Nuclear Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D010641:Phenotype; D018524:Phototropism / Q000187:drug effects; D010940:Plant Proteins; D018514:Plant Structures / Q000187:drug effects / Q000254:growth & development; D030821:Plants, Genetically Modified; D017434:Protein Structure, Tertiary
D029681:Arabidopsis Proteins; D004268:DNA-Binding Proteins; C491592:IAA1 protein, Arabidopsis; C109031:IAA1 protein, plant; D007210:Indoleacetic Acids; D009687:Nuclear Proteins; D010940:Plant Proteins; D003907:Dexamethasone