Germination of photoblastic lettuce seeds is regulated via the control of endogenous physiologically active gibberellin content, rather than of gibberellin responsiveness.
Phytochrome regulates lettuce (Lactuca sativa L. cv. Grand Rapids) seed germination via the control of the endogenous level of bioactive gibberellin (GA). In addition to the previously identified LsGA20ox1, LsGA20ox2, LsGA3ox1, LsGA3ox2, LsGA2ox1, and LsGA2ox2, five cDNAs were isolated from lettuce seeds: LsCPS, LsKS, LsKO1, LsKO2, and LsKAO. Using an Escherichia coli expression system and functional assays, it is shown that LsCPS and LsKS encode ent-copalyl diphosphate synthase and ent-kaurene synthase, respectively. Using a Pichia pastoris system, it was found that LsKO1 and LsKO2 encode ent-kaurene oxidases and LsKAO encodes ent-kaurenoic acid oxidase. A comprehensive expression analysis of GA metabolism genes using the quantitative reverse transcription polymerase chain reaction suggested that transcripts of LsGA3ox1 and LsGA3ox2, both of which encode GA 3-oxidase for GA activation, were primarily expressed in the hypocotyl end of lettuce seeds, were expressed at much lower levels than the other genes tested, and were potently up-regulated by phytochrome. Furthermore, LsDELLA1 and LsDELLA2 cDNAs that encode DELLA proteins, which act as negative regulators in the GA signalling pathway, were isolated from lettuce seeds. The transcript levels of these two genes were little affected by light. Lettuce seeds in which de novo GA biosynthesis was suppressed responded almost identically to exogenously applied GA, irrespective of the light conditions, suggesting that GA responsiveness is not significantly affected by light in lettuce seeds. It is proposed that lettuce seed germination is regulated mainly via the control of the endogenous content of bioactive GA, rather than the control of GA responsiveness.
Sawada
Yoshiaki
Y
Course of the Science of Bioresource, The United Graduate School of Agricultural Science, Iwate University, Morioka, Iwate 020-8550, Japan.
Katsumata
Takumi
T
Kitamura
Jun
J
Kawaide
Hiroshi
H
Nakajima
Masatoshi
M
Asami
Tadao
T
Nakaminami
Kentaro
K
Kurahashi
Toshihiro
T
Mitsuhashi
Wataru
W
Inoue
Yasunori
Y
Toyomasu
Tomonobu
T
D019883:Alkyl and Aryl Transferases / Q000235:genetics / Q000378:metabolism; D003001:Cloning, Molecular; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics / Q000378:metabolism; D018506:Gene Expression Regulation, Plant / Q000528:radiation effects; D018525:Germination / Q000528:radiation effects; D005875:Gibberellins / Q000235:genetics / Q000378:metabolism*; D018545:Lactuca / Q000201:enzymology / Q000235:genetics / Q000378:metabolism* / Q000528:radiation effects; D008027:Light; D006899:Mixed Function Oxygenases / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D012639:Seeds / Q000201:enzymology / Q000235:genetics / Q000378:metabolism* / Q000528:radiation effects; D015398:Signal Transduction / Q000528:radiation effects
D005875:Gibberellins; D010940:Plant Proteins; D003577:Cytochrome P-450 Enzyme System; D006899:Mixed Function Oxygenases; C066398:ent-kaurene oxidase; C423619:ent-kaurenoic acid oxidase; D019883:Alkyl and Aryl Transferases; C090963:ent-kaurene synthetase A; C105712:ent-kaurene synthetase B