AXR2 encodes a member of the Aux/IAA protein family

The dominant gain-of-function axr2-1 mutation of Arabidopsis causes agravit ropic root and shoot growth, a short hypocotyl and stem, and auxin-resistan t 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 aci d) family of auxin-inducible genes. The axr2-1 mutation changes a single am ino acid in conserved domain II of AXR2/IAA7. We isolated loss-of-function mutations in AXX2/IAA7 as intragenic suppressors of axr2-1 or in a screen f or insertion mutations in IAA genes. A null mutant has a slightly longer hy pocotyl than wild-type plants, indicating that AXR2/IAA7 controls developme nt in light-grown seedlings, perhaps in concert with other gene products. D ark-grown axr2-1 mutant plants have short hypocotyls and make leaves, sugge sting that activation of AXR2/IAA7 is sufficient to induce morphological re sponses normally elicited by light. Previously described semidominant mutat ions in two other Arabidopsis IAA genes cause some of the same phenotypes a s axr2-1, but also cause distinct phenotypes. These results illustrate func tional differences among members of the Arabidopsis IAA gene family.