A small acidic protein 1 (SMAP1) mediates responses of the Arabidopsis root to the synthetic auxin 2,4-dichlorophenoxyacetic acid.
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.
Rahman
Abidur
A
Research Group for Plant Resource Application, Japan Atomic Energy Research Institute, Takasaki 370-1292, Japan.
Nakasone
Akari
A
Chhun
Tory
T
Ooura
Chiharu
C
Biswas
Kamal Kanti
KK
Uchimiya
Hirofumi
H
Tsurumi
Seiji
S
Baskin
Tobias I
TI
Tanaka
Atsushi
A
Oono
Yutaka
Y
D015084:2,4-Dichlorophenoxyacetic Acid / Q000494:pharmacology*; D000483:Alleles; D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D002874:Chromosome Mapping; D018506:Gene Expression Regulation, Plant; D018525:Germination; D005966:Glucuronidase / Q000032:analysis; D007210:Indoleacetic Acids / Q000494:pharmacology; D008969:Molecular Sequence Data; D009154:Mutation; D010937:Plant Growth Regulators / Q000494:pharmacology*; D018517:Plant Roots / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism; D034622:RNA Interference; D011993:Recombinant Fusion Proteins / Q000032:analysis; D016415:Sequence Alignment; D015398:Signal Transduction
D029681:Arabidopsis Proteins; D007210:Indoleacetic Acids; D010937:Plant Growth Regulators; D011993:Recombinant Fusion Proteins; C514677:SMAP1 protein, Arabidopsis; D015084:2,4-Dichlorophenoxyacetic Acid; C030737:indoleacetic acid; D005966:Glucuronidase