small acidic protein 1 (SMAP1) mediates responses of the Arabidopsis root to the synthetic auxin 2,4-dichlorophenoxyacetic acid

• Published in: The Plant journal : for cell and molecular biology 2006-09, Vol.47 (5), p.788-801
• Main Authors: Rahman, Abidur, Nakasone, Akari, Chhun, Tory, Ooura, Chiharu, Biswas, Kamal Kanti, Uchimiya, Hirofumi, Tsurumi, Seiji, Baskin, Tobias I, Tanaka, Atsushi, Oono, Yutaka
• Format: Article
• Language: English
• Subjects: 2,4-Dichlorophenoxyacetic Acid - pharmacology; Alleles; Amino Acid Sequence; anti‐auxin; Arabidopsis; Arabidopsis - drug effects; Arabidopsis - genetics; Arabidopsis - metabolism; Arabidopsis Proteins - genetics; Arabidopsis Proteins - metabolism; Arabidopsis Proteins - physiology; Arabidopsis thaliana; Biological and medical sciences; Botany; Cellular biology; Chemical agents; Chromosome Mapping; Flowers & plants; Fundamental and applied biological sciences. Psychology; Gene expression; Gene Expression Regulation, Plant; Germination; Glucuronidase - analysis; Indoleacetic Acids - pharmacology; indole‐3‐acetic acid (IAA); Molecular Sequence Data; Mutation; Plant Growth Regulators - pharmacology; Plant physiology and development; Plant Roots - drug effects; Plant Roots - growth & development; Plant Roots - metabolism; Proteins; p‐chlorophenoxy‐isobutyric acid (PCIB); Recombinant Fusion Proteins - analysis; RNA Interference; Sequence Alignment; Signal Transduction; Vegetative apparatus, growth and morphogenesis. Senescence
• ISSN: 0960-7412; 1365-313X
• DOI: 10.1111/j.1365-313X.2006.02832.x

2,4-dichlorophenoxyacetic acid (2,4-D), a chemical analogue of indole-3-acetic acid (IAA), is widely used as a growth regulator and exogenous source of auxin. Because 2,4-D evokes physiological and molecular responses similar to those evoked by IAA, it is believed that they share a common response pathway. Here, we show that a mutant, antiauxin resistant1 (aar1), identified in a screen for resistance to the anti-auxin p-chlorophenoxy-isobutyric acid (PCIB), is resistant to 2,4-D, yet nevertheless responds like the wild-type to IAA and 1-napthaleneacetic acid in root elongation and lateral root induction assays. That the aar1 mutation alters 2,4-D responsiveness specifically was confirmed by analysis of GUS expression in the DR5:GUS and HS:AXR3NT-GUS backgrounds, as well as by real-time PCR quantification of IAA11 expression. The two characterized aar1 alleles both harbor multi-gene deletions; however, 2,4-D responsiveness was restored by transformation with one of the genes missing in both alleles, and the 2,4-D-resistant phenotype was reproduced by decreasing the expression of the same gene in the wild-type using an RNAi construct. The gene encodes a small, acidic protein (SMAP1) with unknown function and present in plants, animals and invertebrates but not in fungi or prokaryotes. Taken together, these results suggest that SMAP1 is a regulatory component that mediates responses to 2,4-D, and that responses to 2,4-D and IAA are partially distinct.