Isolation and characterization of a rice dwarf mutant with a defect in brassinosteroid biosynthesis.
We have isolated a new recessive dwarf mutant of rice (Oryza sativa L. cv Nipponbare). Under normal growth conditions, the mutant has very short leaf sheaths; has short, curled, and frizzled leaf blades; has few tillers; and is sterile. Longitudinal sections of the leaf sheaths revealed that the cell length along the longitudinal axis is reduced, which explains the short leaf sheaths. Transverse sections of the leaf blades revealed enlargement of the motor cells along the dorsal-ventral axis, which explains the curled and frizzled leaf blades. In addition, the number of crown roots was smaller and the growth of branch roots was weaker than those in the wild-type plant. Because exogenously supplied brassinolide considerably restored the normal phenotypes, we designated the mutant brassinosteroid-dependent 1 (brd1). Further, under darkness, brd1 showed constitutive photomorphogenesis. Quantitative analyses of endogenous sterols and brassinosteroids (BRs) indicated that BR-6-oxidase, a BR biosynthesis enzyme, would be defective. In fact, a 0.2-kb deletion was detected in the genomic region of OsBR6ox (a rice BR-6-oxidase gene) in the brd1 mutant. These results indicate that BRs are involved in many morphological and physiological processes in rice, including the elongation and unrolling of leaves, development of tillers, skotomorphogenesis, root differentiation, and reproductive growth, and that the defect of BR-6-oxidase caused the brd1 phenotype.
Mori
Masaki
M
Department of Molecular Genetics, National Institute of Agrobiological Sciences, Tsukuba, Ibaraki, Japan. morimasa@nias.affrc.go.jp
Nomura
Takahito
T
Ooka
Hisako
H
Ishizaka
Masumi
M
Yokota
Takao
T
Sugimoto
Kazuhiko
K
Okabe
Ken
K
Kajiwara
Hideyuki
H
Satoh
Kouji
K
Yamamoto
Koji
K
Hirochika
Hirohiko
H
Kikuchi
Shoshi
S
D000595:Amino Acid Sequence; D060406:Brassinosteroids; D002777:Cholestanols / Q000378:metabolism*; D003624:Darkness; D035264:Flowers / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D008027:Light; D008969:Molecular Sequence Data; D009154:Mutation; D012275:Oryza / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D010641:Phenotype; D018515:Plant Leaves / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D018517:Plant Roots / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013260:Steroids, Heterocyclic / Q000378:metabolism*
D060406:Brassinosteroids; D002777:Cholestanols; D010940:Plant Proteins; D013260:Steroids, Heterocyclic; D011494:Protein Kinases; C023623:brassinolide