40. シロイヌナズナにおける新奇アブシジン酸輸送体の同定(口頭発表,植物化学調節学会第46回大会)

概要

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In response to water stress, plants increase their endogenous ABA levels and close stomata to limit water loss. It has been shown in Arabidopsis that ABA biosynthetic enzymes are localized in vascular tissues, suggesting that ABA synthesized in vascular tissues is transported to guard cells to close stomata. Two ATP-binding cassette (ABC)-type transporters that mediate ABA export from the inside to the outside of cells (AtABCG25) and ABA uptake from the outside to the inside of cells (AtABCG40), respectively, have been identified. However, the loss-of-function mutants atabcg25 and atabcg40 show milder phenotypes compared to typical ABA-deficient mutants, indicating that the ABA transport system might be highly complex and redundant. We identified a non-ABC-type ABA transporter, AIT1, which mediates cellular ABA uptake. Mutants defective in AIT1 (aitl) were insensitive to exogenously applied ABA during germination, whereas overexpression of AIT1 resulted in ABA-hypersensitivity in the same condition. Interestingly, the inflorescence stems of aitl had a lower surface temperature than those of the wild type because of excess water loss from the stomata. Promoter activities of AIT1 were detected around vascular tissues in inflorescence stems, leaves, and roots. These data suggest that AIT1 functions as an ABA transporter in vivo and plays a role in maintaining the pool size of ABA at the site of ABA biosynthesis.
2011-10-03