In plants,one of the most common modifications of secondary metabolites is methylation catalyzed by various methyltransferases. Recently,a new class of methyltransferases,the SABATH family of methyltransferases,was fo...In plants,one of the most common modifications of secondary metabolites is methylation catalyzed by various methyltransferases. Recently,a new class of methyltransferases,the SABATH family of methyltransferases,was found to modify phytohormones and other small molecules.The SABATH methyltransferases share little sequence similarity with other well characterized methyltransferases.Arabidopsis has 24 members of the SABATH methyltransferase genes,and a subset of them has been shown to catalyze the formation of methyl esters with phytohormones and other small molecules.Physiological and genetic analyses show that methylation of phytohormones plays important roles in regulating various biological processes in plants,including stress responses,leaf development,and seed maturation/germination.In this review,we focus on phytohormone methylation by the SABATH family methyltransferases and the implication of these modifications in plant development.展开更多
Salicylic acid methyltransferase （SAMT）, benzoic acid methyltransferase （BAMT） and theobromine methyltransferase （TH） （henceforth, SABATH） family proteins belong to a unique class of mehtyltransferase that can...Salicylic acid methyltransferase （SAMT）, benzoic acid methyltransferase （BAMT） and theobromine methyltransferase （TH） （henceforth, SABATH） family proteins belong to a unique class of mehtyltransferase that can methylate small molecular compounds Including indole-3-acidic acid （IAA）, salicylic acid （SA） and jasmonic acid （JA）, in plants. Here we report that the GAMT2 protein, which has 34.2% similarity with IAMT1 in the amino acid sequence, can methylate gibberellic acid （GA）. Biolnformatics analysis suggests that GAMT2 may be able to methylate one molecule larger than SA. GAMT2 is predominantly expressed in the developing seed embryo and endosperm in Arabidopsis. During seed germination, the expression of GAMT2 decreases until the cotyledons expand out of the seed coat. Overexpression of GAMT2 in Arabidopsis resulted in multiple phenotypes, including dwarfism, retarded growth, late flowering, and reduced fertility, which are similar to the phenotypes of GA-deficient mutants. Seed germination assay showed that GAMT2 overexpression in plants was hypersensitive to GA biosynthesis inhibitor （ancymidol） and abscisic acid （ABA） treatments, whereas the GAMT2 null mutant （SALK_075450） was slightly Insensitive to such treatments, suggesting that GAMT2 may methylate GA or ABA. Enzyme activity analysis indicated that GAMT2 was able to methylate GA3 into Methyi-GA3 in vitro, but could not methylate ABA. Microarray analysis on GAMT2 overexpression plants suggested that Methyl-GA may be an Inactive form of GA in Arabidopsis. These data suggest that GAMT2 Is Involved in seed maturation and germination by modulating GA activity.展开更多
基金supported by the National Natural Science Foundation of China(90717003)
文摘In plants,one of the most common modifications of secondary metabolites is methylation catalyzed by various methyltransferases. Recently,a new class of methyltransferases,the SABATH family of methyltransferases,was found to modify phytohormones and other small molecules.The SABATH methyltransferases share little sequence similarity with other well characterized methyltransferases.Arabidopsis has 24 members of the SABATH methyltransferase genes,and a subset of them has been shown to catalyze the formation of methyl esters with phytohormones and other small molecules.Physiological and genetic analyses show that methylation of phytohormones plays important roles in regulating various biological processes in plants,including stress responses,leaf development,and seed maturation/germination.In this review,we focus on phytohormone methylation by the SABATH family methyltransferases and the implication of these modifications in plant development.
基金Supported by the National Natural Science Foundation of China （GN 30625002） to LJ Qu.
文摘Salicylic acid methyltransferase （SAMT）, benzoic acid methyltransferase （BAMT） and theobromine methyltransferase （TH） （henceforth, SABATH） family proteins belong to a unique class of mehtyltransferase that can methylate small molecular compounds Including indole-3-acidic acid （IAA）, salicylic acid （SA） and jasmonic acid （JA）, in plants. Here we report that the GAMT2 protein, which has 34.2% similarity with IAMT1 in the amino acid sequence, can methylate gibberellic acid （GA）. Biolnformatics analysis suggests that GAMT2 may be able to methylate one molecule larger than SA. GAMT2 is predominantly expressed in the developing seed embryo and endosperm in Arabidopsis. During seed germination, the expression of GAMT2 decreases until the cotyledons expand out of the seed coat. Overexpression of GAMT2 in Arabidopsis resulted in multiple phenotypes, including dwarfism, retarded growth, late flowering, and reduced fertility, which are similar to the phenotypes of GA-deficient mutants. Seed germination assay showed that GAMT2 overexpression in plants was hypersensitive to GA biosynthesis inhibitor （ancymidol） and abscisic acid （ABA） treatments, whereas the GAMT2 null mutant （SALK_075450） was slightly Insensitive to such treatments, suggesting that GAMT2 may methylate GA or ABA. Enzyme activity analysis indicated that GAMT2 was able to methylate GA3 into Methyi-GA3 in vitro, but could not methylate ABA. Microarray analysis on GAMT2 overexpression plants suggested that Methyl-GA may be an Inactive form of GA in Arabidopsis. These data suggest that GAMT2 Is Involved in seed maturation and germination by modulating GA activity.
