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.

SOMNUS, a CCCH-Type Zinc Finger Protein inArabidopsis, Negatively Regulates Light-Dependent Seed Germination Downstream of PIL5

“…Quantification of Endogenous ABA and GA Levels GA measurements were performed on a liquid chromatography-tandem mass spectrometry system consisting of a quadrupole/time-of-flight tandem mass spectrometer (Q-Tof Premier; Waters) and an Acquity Ultra Performance liquid chromatograph (Waters) equipped with a reversephase column (Acquity UPLC BEH-C18; Waters), as described previously (Varbanova et al, 2007). 2 H-labeled GAs (purchased from Lewis Mander, Australian National University) were used as internal standards.…”

Genetic Analysis Reveals That C19-GA 2-Oxidation Is a Major Gibberellin Inactivation Pathway inArabidopsis

“…However, it is not clear to what extent this is a general mechanism that occurs in other plant species. Secondly, methyl transferases specific for GAs have been described in Arabidopsis thaliana, where expression is mainly localized to developing seeds, and analysis of loss-offunction mutants suggests a role in GA inactivation in seed tissues (Varbanova et al, 2007), although accumulation of methylated GAs has not yet been demonstrated.…”

Biosynthesis and emission of insect-induced methyl salicylate and methyl benzoate from rice

“…SAMT and BAMT belong to a protein family called the SABATH [7]. In addition to SA and BA, other known carboxylic acid substrates of the SABATH family include jasmonic acid (JA) [34], indole-3-acetic acid [31,44e46], gibberellic acids [41], farnesoic acid [42], cinnamic acid and p-coumaric acid [16] and loganic acid [21]. Other members of the SABATH family are involved in caffeine biosynthesis by catalyzing nitrogen methylation [25].…”