Arabidopsis ABCG27 plays an essential role in flower and leaf development by modulating abscisic acid content

Abscisic acid (ABA) is a phytohormone that mediates stress responses and regulates plant development. Several ATP-binding cassette (ABC) transporters in the G subfamily of ABC (ABCG) proteins have been reported to transport ABA. We investigated whether there are any other ABCG proteins that mediate plant developmental processes regulated by ABA in Arabidopsis (Arabidopsis thaliana). The ABCG27 gene was upregulated in response to exogenous ABA treatment. The abcg27 knockout mutant exhibited two developmental defects: epinastic leaves and abnormally long pistils, which reduced fertility and silique length. ABCG27 expression was induced 3-fold when flower buds were exposed to exogenous ABA, and the promoter of ABCG27 had two ABA-responsive elements. ABA content in the pistil and true leaves were increased in the abcg27 knockout mutant. Detached abcg27 pistils exposed to exogenous ABA grew longer than those of the wild-type control. ABCG27 fused to GFP localized to the plasma membrane when expressed in Arabidopsis mesophyll protoplasts. A transcriptome analysis of the pistils and true leaves of the wild type and abcg27 knockout mutant revealed that the expression of organ development-related genes changed in the knockout mutant. In particular, the expression of trans-acting small interference (ta-si) RNA processing enzyme genes, which regulate flower and leaf development, was low in the knockout mutant. Together, these results suggest that ABCG27 most likely function as an ABA transporter at the plasma membrane, modulating ABA levels and thereby regulating the development of the pistils and leaves under normal, non-stressed conditions

Plant ABC transporters enable many unique aspects of a terrestrial plant's lifestyle

Terrestrial plants have two to four times more ATP-binding cassette (ABC) transporter genes than other organisms, including their ancestral microalgae. Recent studies found that plants harboring mutations in these transporters exhibit dramatic phenotypes, many of which are related to developmental processes and functions necessary for life on dry land. These results suggest that ABC transporters multiplied during evolution and assumed novel functions that allowed plants to adapt to terrestrial environmental conditions. Examining the literature on plant ABC transporters from this viewpoint led us to propose that diverse ABC transporters enabled many unique and essential aspects of a terrestrial plant's lifestyle, by transporting various compounds across specific membranes of the plant