Plant Physiol, December 2002, Vol. 130, pp. 1797-1806
Molecular Characterization of a Novel Gene Family Encoding ACT
Domain Repeat Proteins in Arabidopsis
Ming-Hsiun
Hsieh and
Howard
M.
Goodman*
Department of Genetics, Harvard Medical School, and Department of
Molecular Biology, Massachusetts General Hospital, Boston,
Massachusetts 02114
In bacteria, the regulatory ACT domains serve as amino acid-binding
sites in some feedback-regulated amino acid metabolic enzymes. We have
identified a novel type of ACT domain-containing protein family in
Arabidopsis whose members contain ACT domain repeats (the "ACR"
protein family). There are at least eight ACR genes located on each of
the five chromosomes in the Arabidopsis genome. Gene structure
comparisons indicate that the ACR gene family may have arisen by gene
duplications. Northern-blot analysis indicates that each member of the
ACR gene family has a distinct expression pattern in various organs
from 6-week-old Arabidopsis. Moreover, analyses of an ACR3
promoter-
-glucuronidase (GUS) fusion in transgenic Arabidopsis
revealed that the GUS activity formed a gradient in the developing
leaves and sepals, whereas low or no GUS activity was detected in the
basal regions. In 2-week-old Arabidopsis seedlings grown in tissue
culture, the expression of the ACR gene family is differentially
regulated by plant hormones, salt stress, cold stress, and light/dark
treatment. The steady-state levels of ACR8 mRNA are dramatically
increased by treatment with abscisic acid or salt. Levels of ACR3 and
ACR4 mRNA are increased by treatment with benzyladenine. The amino acid
sequences of Arabidopsis ACR proteins are most similar in the ACT
domains to the bacterial sensor protein GlnD. The ACR proteins may
function as novel regulatory or sensor proteins in plants.
*
Corresponding author; e-mail
goodman{at}molbio.mgh.harvard.edu; fax 617-726-3535.
© 2002 American Society of Plant Biologists
