title: Methylation of gibberellins by Arabidopsis GAMT1 and GAMT2.
abstract: 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.
authors.affiliation: Department of Molecular, Cellular, and Developmental Biology, University of Michigan, An Arbor, Michigan 48109-1048, USA.
authors.forename: Marina
authors.initials: M
authors.lastname: Varbanova
authors.forename: Shinjiro
authors.initials: S
authors.lastname: Yamaguchi
authors.forename: Yue
authors.initials: Y
authors.lastname: Yang
authors.forename: Katherine
authors.initials: K
authors.lastname: McKelvey
authors.forename: Atsushi
authors.initials: A
authors.lastname: Hanada
authors.forename: Roy
authors.initials: R
authors.lastname: Borochov
authors.forename: Fei
authors.initials: F
authors.lastname: Yu
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Jikumaru
authors.forename: Jeannine
authors.initials: J
authors.lastname: Ross
authors.forename: Diego
authors.initials: D
authors.lastname: Cortes
authors.forename: Choong Je
authors.initials: CJ
authors.lastname: Ma
authors.forename: Joseph P
authors.initials: JP
authors.lastname: Noel
authors.forename: Lew
authors.initials: L
authors.lastname: Mander
authors.forename: Vladimir
authors.initials: V
authors.lastname: Shulaev
authors.forename: Yuji
authors.initials: Y
authors.lastname: Kamiya
authors.forename: Steve
authors.initials: S
authors.lastname: Rodermel
authors.forename: David
authors.initials: D
authors.lastname: Weiss
authors.forename: Eran
authors.initials: E
authors.lastname: Pichersky
mesh_terms: 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
chemical_list: D029681:Arabidopsis Proteins; D005875:Gibberellins; D012333:RNA, Messenger; C519869:GAMT1 protein, Arabidopsis; C519870:GAMT2 protein, Arabidopsis; D008780:Methyltransferases