exhibited a similar dwarf phenotype as the control grafting of
abcg14/abcg14 (Fig. 5A, Lower Right and Lower Left, and B),
indicating that atabcg14 roots could not transport sufficient
cytokinins to support normal growth and development of the
shoot. These results suggest that AtABCG14-mediated rootto-
shoot translocation of cytokinins is crucial for shoot growth
and development.
Discussion
Cytokinins have long since been known to be transported from
the root to the shoot via xylem (2). However, the molecular
mechanism whereby cytokinin is transported into the xylem has
been elusive. Our results strongly suggest that AtABCG14 is
engaged in a critical step in cytokinin transport in roots—namely,
it is involved in a step that loads cytokinin into the xylem of the
root, facilitating its transfer to the shoot (Fig. 5C). The following
lines of evidence presented in this work support this conclusion:
(i) atabcg14 knockout plants phenocopied cytokinin biosynthesis