Abstract
Stomatal regulation is important for water transpiration from plants. Stomatal opening and closing are controlled by many transporter proteins in guard cells. AtABCG22 is a member of the ATP-binding cassette (ABC) transporters and is a stomatal regulator; however, the function of AtABCG22 has not yet been determined fully, although a mutant phenotype included a significant effect on stomatal status. Here, we further investigated the function of the AtABCG22 gene and its functional relationships with other subfamily genes. Among close family members, we found a functional relationship of stomatal phenotypes with AtABCG21, which is also expressed specifically in guard cells. Based on an analysis of double mutants, adding the atabcg21 mutation to atabcg22 mutant partially suppressed the open-stomata phenotype of atabcg22. Multiple-mutant analyses indicated that this suppression was independent of abscisic acid signaling in guard cells. We also found that atabcg22 mutant showed a unique time course-dependent phenotype, being defective in maintenance of stomatal status after initial stomatal opening elicited by light signaling. The function of AtABCG22 and its relationship with AtABCG21 in stomatal regulation are considered.
Highlights
Stomata consist of a pair of guard cells, a unique cell type with an important role in regulating water transpiration from plant surfaces
We previously reported AtABCG22 was involved in stomatal regulation, because atabcg[22] mutants that exhibited a typical open-stomata (OST) phenotype[30]
To study the relationship between AtABCG22 and other ABCG members that were closely related based on a phylogenetic tree[17,30], we focused one of the family members, AtABCG21
Summary
Stomata consist of a pair of guard cells, a unique cell type with an important role in regulating water transpiration from plant surfaces. The superfamily of ATP-binding cassette (ABC) transporters is one of the most abundant protein families in nature. AtABCG26 is essential for exine formation, by transporting polyketide sporopollenin precursors[24,25,26,27,28,29] Most of these transporters are related to roles in maintaining water content or in prohibiting water loss from plant bodies or pollen cells. In addition to the members above, we previously isolated AtABCG22, which functions in retaining water in plants[30]. Mutant AtABCG22 plants show increased water transpiration and drought susceptibility, suggesting a relationship with ABA function. Exhibited an additive effect to ABA signaling or ABA biosynthesis, so that the function of AtABCG22 in guard cells remains to be determined
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