C. Timpte et al., THE AXR2-1 MUTATION OF ARABIDOPSIS-THALIANA IS A GAIN-OF-FUNCTION MUTATION THAT DISRUPTS AN EARLY STEP IN AUXIN RESPONSE, Genetics, 138(4), 1994, pp. 1239-1249
The dominant axr2-1 mutation of Arabidopsis thaliana confers resistanc
e to the plant hormones auxin, ethylene, and abscisic acid. In additio
n, axr2-1 has pleiotropic effects on plant morphology which include gr
avitropic defects in roots, hypocotyls and inflorescences of axr2-1 pl
ants. Two genetic screens were conducted to isolate new mutations at t
he AXR2 locus. First, axr2-1 pollen was gamma-irradiated, crossed onto
wild-type plants, and the M(1) progeny screened for loss of the axr2-
1 phenotype. Large deletions of the axr2-1 region on chromosome 3 resu
lted; however, none of these deletions appeared to be heritable. In th
e second, M(2) seed obtained from axr2-1 gl-l plants was screened for
reversion of the axr2-1 phenotype. One revertant line, axr2-r3, has a
distinctive phenotype caused by a second mutation at the axr2 locus. T
o learn more about the nature of the axr2-1 mutation, the effects of v
arying the ratio of wild-type to mutant copies of the AXR2 gene were e
xamined by comparing plants of the following genotypes: +/+, +/+/+, ax
r2-1/axr2-1, axr2-1/+ and axr2-1/+/+. Additionally, accumulation of tr
anscripts from the auxin-inducible SAUR-AC1 gene was examined to deter
mine the response of wild-type and mutant plants to auxin. Wild-type s
eedlings and mature plants accumulate transcripts with auxin treatment
. In contrast, axr2-1 tissue does not accumulate SAUR-AC1 transcripts
in response to auxin. Taken together, these results indicate that axr2
-1 is a neomorphic or hypermorphic mutation that disrupts an early ste
p in an auxin response pathway.