Methylation of gibberellins by Arabidopsis GAMT1 and GAMT2.
Arabidopsis thaliana GAMT1 and GAMT2 encode enzymes that catalyze formation of the methyl esters of gibberellins (GAs). Ectopic expression of GAMT1 or GAMT2 in Arabidopsis, tobacco (Nicotiana tabacum), and petunia (Petunia hybrida) resulted in plants with GA deficiency and typical GA deficiency phenotypes, such as dwarfism and reduced fertility. GAMT1 and GAMT2 are both expressed mainly in whole siliques (including seeds), with peak transcript levels from the middle until the end of silique development. Within whole siliques, GAMT2 was previously shown to be expressed mostly in developing seeds, and we show here that GAMT1 expression is also localized mostly to seed, suggesting a role in seed development. Siliques of null single GAMT1 and GAMT2 mutants accumulated high levels of various GAs, with particularly high levels of GA(1) in the double mutant. Methylated GAs were not detected in wild-type siliques, suggesting that methylation of GAs by GAMT1 and GAMT2 serves to deactivate GAs and initiate their degradation as the seeds mature. Seeds of homozygous GAMT1 and GAMT2 null mutants showed reduced inhibition of germination, compared with the wild type, when placed on plates containing the GA biosynthesis inhibitor ancymidol, with the double mutant showing the least inhibition. These results suggest that the mature mutant seeds contained higher levels of active GAs than wild-type seeds.
Varbanova
Marina
M
Department of Molecular, Cellular, and Developmental Biology, University of Michigan, An Arbor, Michigan 48109-1048, USA.
Yamaguchi
Shinjiro
S
Yang
Yue
Y
McKelvey
Katherine
K
Hanada
Atsushi
A
Borochov
Roy
R
Yu
Fei
F
Jikumaru
Yusuke
Y
Ross
Jeannine
J
Cortes
Diego
D
Ma
Choong Je
CJ
Noel
Joseph P
JP
Mander
Lew
L
Shulaev
Vladimir
V
Kamiya
Yuji
Y
Rodermel
Steve
S
Weiss
David
D
Pichersky
Eran
E
D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D001483:Base Sequence; D018525:Germination; D005875:Gibberellins / Q000378:metabolism*; D008745:Methylation; D008780:Methyltransferases / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D008969:Molecular Sequence Data; D032306:Petunia / Q000235:genetics / Q000378:metabolism; D010641:Phenotype; D012333:RNA, Messenger / Q000032:analysis / Q000378:metabolism; D012639:Seeds / Q000254:growth & development / Q000378:metabolism; D016415:Sequence Alignment; D014026:Nicotiana / Q000235:genetics / Q000378:metabolism
D029681:Arabidopsis Proteins; D005875:Gibberellins; D012333:RNA, Messenger; C519869:GAMT1 protein, Arabidopsis; C519870:GAMT2 protein, Arabidopsis; D008780:Methyltransferases