Methylation of gibberellins by Arabidopsis GAMT1 and GAMT2
Methylation of gibberellins by Arabidopsis GAMT1 and GAMT2
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DOI：
10.1105/tpc.106.044602
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发表时间：
2007-01-01
期刊：
影响因子：
11.6
通讯作者：
Pichersky, Eran
中科院分区：
文献类型：
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作者：
Varbanova, Marina;Yamaguchi, Shinjiro;Pichersky, Eran
拟南芥GAMT1和GAMT2编码催化赤霉素甲酯（GA）形成的酶。GAMT1或GAMT2在拟南芥、烟草（Nicotiana tabacum）和矮牵牛（Petunia hybrida）中的异位表达导致具有GA缺乏和典型的GA缺乏表型的植物，例如侏儒症和降低的生育力。GAMT1和GAMT2都主要在整个长角果（包括种子）中表达，从长角果发育的中间直到结束都有峰值转录水平。在整个角果，GAMT2以前被证明是主要在发育中的种子中表达，我们在这里表明，GAMT1的表达也主要定位于种子，这表明在种子发育中的作用。GAMT1和GAMT2单突变体的玉米穗积累了高水平的各种GA，在双突变体中GA（1）的水平特别高。在野生型长角果中未检测到甲基化的GAs，这表明GAMT1和GAMT2对GAs的甲基化起到使GAs失活并在种子成熟时开始其降解的作用。纯合GAMT1和GAMT2无效突变体的种子表现出降低的发芽抑制，与野生型相比，当放置在含有GA生物合成抑制剂ancymidol的平板上时，双突变体表现出最少的抑制。这些结果表明，成熟的突变体种子比野生型种子含有更高水平的活性GAs。
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.