Abstract
The plant hormone abscisic acid (ABA) is actively synthesized in vascular tissues and transported to guard cells to promote stomatal closure. Although several transmembrane ABA transporters have been identified, how the movement of ABA within plants is regulated is not fully understood. In this study, we determined that Arabidopsis NPF4.6, previously identified as an ABA transporter expressed in vascular tissues, is also present in guard cells and positively regulates stomatal closure in leaves. We also found that mutants defective in NPF5.1 had a higher leaf surface temperature compared to the wild type. Additionally, NPF5.1 mediated cellular ABA uptake when expressed in a heterologous yeast system. Promoter activities of NPF5.1 were detected in several leaf cell types. Taken together, these observations indicate that NPF5.1 negatively regulates stomatal closure by regulating the amount of ABA that can be transported from vascular tissues to guard cells.
Highlights
Genes 2021, 12, 885. https://doi.org/The plant hormone abscisic acid (ABA) plays crucial roles in various processes such as seed development, germination and responses to abiotic and biotic stresses [1,2,3]
We previously showed that NPF4.6 functions as an ABA importer in Arabidopsis [35]
The inflorescence stems of mutants defective in NPF4.6 had lower surface temperatures with more open stomata; the mutants did not show any clear leaf phenotypes, presumably due to redundancies with other ABA transporters
Summary
The plant hormone abscisic acid (ABA) plays crucial roles in various processes such as seed development, germination and responses to abiotic and biotic stresses [1,2,3]. These physiological responses are associated with changes in endogenous ABA levels. Expression of NCED3 is rapidly induced upon water deficit [11,14], whereas mRNA levels of NCED6 and NCED9 are regulated by environmental factors that affect seed dormancy and germination (e.g., light and temperature) during imbibition [15,16]. ABA 8’-hydroxylase, belonging to the CYP707A subfamily of cytochrome
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