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. 2000 Jun;123(2):563-74.
doi: 10.1104/pp.123.2.563.

AXR2 encodes a member of the Aux/IAA protein family

P Nagpal  1 , L M Walker, J C Young, A Sonawala, C Timpte, M Estelle, J W Reed
Affiliations

AXR2 encodes a member of the Aux/IAA protein family

P Nagpal et al. Plant Physiol. 2000 Jun.

Abstract

The dominant gain-of-function axr2-1 mutation of Arabidopsis causes agravitropic root and shoot growth, a short hypocotyl and stem, and auxin-resistant root growth. We have cloned the AXR2 gene using a map-based approach, and find that it is the same as IAA7, a member of the IAA (indole-3-acetic acid) family of auxin-inducible genes. The axr2-1 mutation changes a single amino acid in conserved domain II of AXR2/IAA7. We isolated loss-of-function mutations in AXR2/IAA7 as intragenic suppressors of axr2-1 or in a screen for insertion mutations in IAA genes. A null mutant has a slightly longer hypocotyl than wild-type plants, indicating that AXR2/IAA7 controls development in light-grown seedlings, perhaps in concert with other gene products. Dark-grown axr2-1 mutant plants have short hypocotyls and make leaves, suggesting that activation of AXR2/IAA7 is sufficient to induce morphological responses normally elicited by light. Previously described semidominant mutations in two other Arabidopsis IAA genes cause some of the same phenotypes as axr2-1, but also cause distinct phenotypes. These results illustrate functional differences among members of the Arabidopsis IAA gene family.

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Figures

Figure 1
Figure 1
A, Mutations in AXR2/IAA7. The box represents the coding part of the gene. Dark vertical lines within the box indicate positions of introns. Stippled boxes indicate conserved domains I, II, III, and IV. B, Mutations in conserved domain II of AXR2/IAA7, AXR3/IAA17, and SHY2/IAA3 proteins.
Figure 2
Figure 2
A, Southern hybridization of wild-type (+) and axr2-5 (−) DNA cut with BglII or NsiI restriction enzymes and probed with an AXR2/IAA7 probe (left) or a T-DNA probe (right). Horizontal bars indicate bands present in wild-type DNA but missing in the mutant, and asterisks indicate bands that are unique to the mutant and hybridize to both probes. B and C, Northern blots of mRNA from axr2 mutants probed with AXR2/IAA7 cDNA probes. B, mRNA from wild-type Wassilewskija and axr2-5, probed with a PCR product derived from an AXR2/IAA7 cDNA; C, mRNA from wild-type Columbia, axr2-1, and intragenic suppressors derived from axr2-1, probed with the 3′-untranslated region of the AXR2/IAA7 cDNA. Hybridizations of the same two blots with a β-tubulin probe show that the amount of mRNA loaded was roughly equal in each lane (lower panels).
Figure 3
Figure 3
Growth phenotypes of the axr2-5 T-DNA insertion mutant. A, Kinetics of root elongation in light-grown seedlings; B, kinetics of hypocotyl elongation in light-grown seedlings; C, root growth in the presence of varying amounts of IAA; D, kinetics of root elongation of dark-grown seedlings; E, kinetics of hypocotyl elongation of dark-grown seedlings. Error bars indicate sds of measurements.
Figure 4
Figure 4
Effects of axr2-1 and axr3-1 mutations on light responses. A, Hypocotyl lengths of wild-type, axr2-1, and axr3-1 seedlings grown for 5 d under different light conditions, normalized to the wild-type hypocotyl length in the dark ± sd. B, Hypocotyl lengths of wild-type, axr2-1, axr3-1, phyB-9, axr2-1 phyB-9, and axr3-1 phyB-9 seedlings grown for 7 d in red light ± sd.
Figure 5
Figure 5
Appearance of wild-type, axr2-1, axr3-1, and det1-1 mutant seedlings after 23 d growth in the dark.
Figure 6
Figure 6
Appearance of Columbia/Landsberg erecta hybrid plants heterozygous for axr2-1, axr3-1, shy2-2, or shy2-3. Seedlings were grown on vertically oriented MS/agar/2% (w/v) Suc plates for 7 d. As shown in the photograph, axr3-1/+ seedlings frequently grew in orientations other than upright.
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