Lesions in the sterol delta reductase gene of Arabidopsis cause dwarfism due to a block in brassinosteroid biosynthesis.
The brassinosteroid (BR) biosynthetic pathway, and the sterol pathway which is prerequisite to the BR pathway, are rapidly being characterized because of the availability of a large number of characteristic dwarf mutants in Arabidopsis. Here we show that the Arabidopsis dwarf5 mutants are disrupted in a sterol Delta7 reduction step. dwf5 plants display the characteristic dwarf phenotype typical of other BR mutants. This phenotype includes small, round, dark-green leaves, and short stems, pedicels, and petioles. Metabolite tracing with 13C-labeled precursors in dwf5 verified a deficiency in a sterol Delta7 reductase activity. All six independent alleles contain loss-of-function mutations in the sterol Delta7 reductase gene. These include a putative mRNA instability mutation in dwf5-1, 3' and 5' splice-site mutations in dwf5-2 and dwf5-6, respectively, premature stop codons in dwf5-3 (R400Z) and dwf5-5 (R409Z), and a mis-sense mutation in dwf5-4 (D257N). The dwf5 plant could be restored to wild type by ectopic overexpression of the wild-type copy of the gene. Both the Arabidopsis dwf5 phenotype and the human Smith-Lemli-Opitz syndrome are caused by loss-of-function mutations in a sterol Delta7 reductase gene, indicating that it is required for the proper growth and development of these two organisms.
Choe
S
S
Department of Plant Sciences, University of Arizona, Tucson, Arizona 85721, USA.
Tanaka
A
A
Noguchi
T
T
Fujioka
S
S
Takatsuto
S
S
Ross
A S
AS
Tax
F E
FE
Yoshida
S
S
Feldmann
K A
KA
D000483:Alleles; D000595:Amino Acid Sequence; D000818:Animals; D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D029681:Arabidopsis Proteins; D001483:Base Sequence; D015152:Blotting, Northern; D003001:Cloning, Molecular; D018076:DNA, Complementary; D006801:Humans; D008969:Molecular Sequence Data; D009154:Mutation; D010088:Oxidoreductases / Q000235:genetics*; D044925:Oxidoreductases Acting on CH-CH Group Donors; D010937:Plant Growth Regulators / Q000096:biosynthesis*; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics*; D012326:RNA Splicing; D012333:RNA, Messenger / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D013256:Steroids / Q000096:biosynthesis*
D029681:Arabidopsis Proteins; D018076:DNA, Complementary; D010937:Plant Growth Regulators; D010940:Plant Proteins; D012333:RNA, Messenger; D013256:Steroids; C033144:lathosterol delta-5-dehydrogenase; D010088:Oxidoreductases; D044925:Oxidoreductases Acting on CH-CH Group Donors; C407913:DWF5 protein, Arabidopsis