Arabidopsis ABCG14 protein controls the acropetal translocation of root-synthesized cytokinins

Abstract

Cytokinins are a major group of phytohormones regulating plant growth, development and stress responses. However, in contrast to the well-defined polar transport of auxins, the molecular basis of cytokinin transport is poorly understood. Here we show that an ATP-binding cassette transporter in Arabidopsis, AtABCG14, is essential for the acropetal (root to shoot) translocation of the root-synthesized cytokinins. AtABCG14 is expressed primarily in the pericycle and stelar cells of roots. Knocking out AtABCG14 strongly impairs the translocation of trans-zeatin (tZ)-type cytokinins from roots to shoots, thereby affecting the plant's growth and development. AtABCG14 localizes to the plasma membrane of transformed cells. In planta feeding of C 14 or C 13 -labelled tZ suggests that it acts as an efflux pump and its presence in the cells directly correlates with the transport of the fed cytokinin. Therefore, AtABCG14 is a transporter likely involved in the long-distance translocation of cytokinins in planta.

Cell-Type-Specific Cytokinin Distribution within the Arabidopsis Primary Root Apex

“…In Arabidopsis, the highest expression of a CK hydroxylase involved in biosynthesis of trans-zeatin (CYP735A2) is in the vasculature (Kiba et al, 2013) along with the cytokinin transporter (ABCG14) (Ko et al, 2014;Zhang et al, 2014), while cytokinin oxidase/dehydrogenase (CKX4) is expressed in the root cap. CKX5 and CKX6 expression is detected in the root vasculature with and without reaching the QC cells, respectively (Werner et al, 2003).…”

“…Genetic studies of both PUPs and ENTs are hampered by the large number of genes in each family and by the fact that the proteins appear also to transport non-CK purine molecules in addition to CKs. The ATP binding cassette transporter subfamily G14 (ABCG14) has recently been shown to regulate entry of zeatin-type CKs into the xylem transport stream and hence may function primarily in long-distance export from root to shoot rather than local transport (Ko et al, 2014;Zhang et al, 2014).…”

The Yin-Yang of Hormones: Cytokinin and Auxin Interactions in Plant Development

“…Furthermore, an ATP binding cassette transporter (ABCG14) has been shown to be necessary for the movement of cytokinin, primarily trans-zeatin forms, from roots to shoots (Ko et al, 2014;Zhang et al, 2014).…”

Insights into the Origin and Evolution of the Plant Hormone Signaling Machinery

“…CYTOKININ RESPONSES FACTORs positively regulate the transcription response to CKs. CKs are transported by ABCG14 in the long distance from root to shoot (Zhang et al, 2014).…”