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DEVELOPMENT AND HORMONE ACTION

Altered Life Cycle in Arabidopsis Plants Expressing PsUGT1, a UDP-Glucuronosyltransferase-Encoding Gene from Pea¹

Division of Plant Pathology and Microbiology, Department of Plant Sciences, University of Arizona, Tucson, Arizona 85721 (H.-H.W., M.C.H.); and Department of Molecular, Cell and Developmental Biology (H.-H.W., A.M.H.), Department of Chemistry (K.F.F.), and Molecular Biology Institute (A.M.H.), University of California, Los Angeles, California 90095

Alfalfa (Medicago sativa) and Arabidopsis were used as model systems to examine molecular mechanisms underlying developmental effects of a microsomal UDP-glucuronosyltransferase-encoding gene from pea (Pisum sativum; PsUGT1). Alfalfa expressing PsUGT1 antisense mRNA under the control of the cauliflower mosaic virus (CaMV) 35S promoter exhibited delayed root emergence, reduced root growth, and increased lateral root development. The timing of root emergence in wild-type and antisense plants was correlated with the transient accumulation of auxin at the site of root emergence. Cell suspension cultures derived from the antisense alfalfa plants exhibited a delay in cell cycle from 24-h in the wild-type plants to 48-h in the antisense plants. PsUGT1::uidA was introduced into Arabidopsis to demonstrate that, as in alfalfa and pea, PsUGT1 expression occurs in regions of active cell division. This includes the root cap and root apical meristems, leaf primordia, tips of older leaves, and the transition zone between the hypocotyl and the root. Expression of PsUGT1::uidA colocalized with the expression of the auxin-responding reporter DR5::uidA. Co-expression of DR5::uidA in transgenic Arabidopsis lines expressing CaMV35S::PsUGT1 revealed that ectopic expression of CaMV35S::PsUGT1 is correlated with a change in endogenous auxin gradients in roots. Roots of ecotype Columbia expressing CaMV35S::PsUGT1 exhibited distinctive responses to exogenous naphthalene acetic acid. Completion of the life cycle occurred in 4 to 6 weeks compared with 6 to 7 weeks for wild-type Columbia. Inhibition of endogenous ethylene did not correct this early senescence phenotype.

¹ This work was supported by the National Science Foundation (to M.C.H. and H.-H.W.), by the Department of Energy, Division of Energy Biosciences (to M.C.H. and H.-H.W.), by the University of Arizona College of Agriculture and Life Sciences Experiment Station, and by the National Institutes of Health (grant no. NCCAMSPSO AT00151 to the Center for Dietary Supplement Research Botanicals at University of California, Los Angeles to A.M.H. [director, Agricultural Botany Core] and H.-H.W. [junior investigator]). The National Science Foundation is acknowledged for partial support for purchase of mass spectrometric instrumentation (CHE grant no. 007829).

^* Corresponding author; e-mail hhwoo{at}ucla.edu; fax 310–206–5413.

Received May 3, 2003; returned for revision May 23, 2003; accepted May 30, 2003.

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