First published online May 2, 2002; 10.1104/pp.001982
Plant Physiol, June 2002, Vol. 129, pp. 585-593
SOS4, A Pyridoxal Kinase Gene, Is Required for Root
Hair Development in Arabidopsis1
Huazhong
Shi2 and
Jian-Kang
Zhu*
Department of Plant Sciences, University of Arizona, Tucson,
Arizona 85721
Root hair development in plants is controlled by many
genetic, hormonal, and environmental factors. A number of genes have been shown to be important for root hair formation. Arabidopsis salt overly sensitive 4 mutants were originally
identified by screening for NaCl-hypersensitive growth. The
SOS4 (Salt Overly Sensitive 4) gene was
recently isolated by map-based cloning and shown to encode a pyridoxal
(PL) kinase involved in the production of PL-5-phosphate, which is an
important cofactor for various enzymes and a ligand for certain ion
transporters. The root growth of sos4 mutants is slower
than that of the wild type. Microscopic observations revealed that
sos4 mutants do not have root hairs in the maturation
zone. The sos4 mutations block the initiation of most
root hairs, and impair the tip growth of those that are initiated. The
root hairless phenotype of sos4 mutants was complemented by the wild-type SOS4 gene. SOS4
promoter- -glucuronidase analysis showed that
SOS4 is expressed in the root hair and other hair-like structures. Consistent with SOS4 function as a PL kinase, in vitro application of pyridoxine and pyridoxamine, but not PL, partially rescued the root hair defect in sos4 mutants.
1-Aminocyclopropane-1-carboxylic acid and 2,4-dichlorophenoxyacetic
acid treatments promoted root hair formation in both wild-type and
sos4 plants, indicating that genetically
SOS4 functions upstream of ethylene and auxin in root hair development. The possible role of SOS4 in ethylene and auxin biosynthesis is discussed.
1
This work was supported by the U.S. National
Institutes of Health (grant no. R01GM59138 to J.-K.Z.).
2
Present address: Department of Pomology, University of
California, One Shields Avenue, Davis, CA 95616.
*
Corresponding author; e-mail jkzhu{at}ag.arizona.edu; fax
520-621-7186.
© 2002 American Society of Plant Physiologists
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