A Developmental Framework for Graft Formation and Vascular Reconnection in Arabidopsis thaliana.
2015
Plant grafting is a biologically important phenomenon
involving the physical joining of two plants to
generate a chimeric organism. It is widely practiced
in horticulture and used in science to study the
long-distance movement of molecules. Despite its
widespread use, the mechanism of graft formation
and vascular reconnection is not well understood.
Here, we study the dynamics and mechanisms of
vascular regeneration in Arabidopsis thaliana during
graft formation when the vascular strands are severed
and reconnected. We demonstrate a temporal
separation between tissue attachment, phloem connection,
root growth, and xylem connection. By
analyzing cell division patterns and hormone responses
at the graft junction, we found that tissues
initially show an asymmetry in cell division, cell differentiation,
and gene expression and, through contact
with the opposing tissue, lose this asymmetry and reform
the vascular connection. In addition, we identified
genes involved in vascular reconnection at the
graft junction and demonstrate that these auxin
response genes are required below the graft junction.
We propose an inter-tissue communication
process that occurs at the graft junction and promotes
vascular connection by tissue-specific auxin
responses involving ABERRANT LATERAL ROOT
FORMATION 4 (ALF4). Our study has implications
for phenomena where forming vascular connections
are important including graft formation, parasitic
plant infection, and wound healing.
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