Abstract
Abscission is a universal and dynamic process in plants whereby organs
such as leaves, flowers and fruit are shed, both during normal development,
and in response to tissue damage and stress. Shedding occurs
by separation of cells in anatomically distinct regions of the plant, called
abscission zones (AZs). During abscission, the plant hormone ethylene stimulates
cells to produce enzymes that degrade the middle lamella between cells in
the AZ. The physiology and regulation of abscission at fully developed AZs
is well known, but the molecular biology underlying their
development is not. Here we report the first isolation of a gene directly
involved in the development of a functional plant AZ. Tomato plants with the
jointless mutation fail to develop AZs on their pedicels
and so abscission of flowers or fruit does not occur normally. We identify
JOINTLESS as a new MADS-box gene in a distinct phylogenetic clade separate
from those functioning in floral organs. We propose that a deletion in
JOINTLESS accounts for the failure of activation of pedicel AZ development
in jointless tomato plants.