May 9, 2006
Proceedings of the U.S. National Academy of Sciences (PNAS)
Ripening in the tomato
Green-ripe mutant is inhibited by ectopic expression of a
protein that disrupts ethylene signaling
Cornelius S. Barry, Boyce Thompson Institute
for Plant Research, Ithaca, NY 14853
and James J. Giovannoni,
Boyce Thompson Institute for Plant Research, Ithaca, NY 14853;
and U.S. Department of Agriculture/Agriculture Research Service,
Plant, Soil, and Nutrition Laboratory, Ithaca, NY 14853
Communicated by Steven D.
Tanksley, Cornell University, Ithaca, NY, March 21, 2006
(received for review February 1, 2006)
ABSTRACT
To achieve full ripening,
climacteric fruits, such as tomato require synthesis, perception
and signal transduction of the plant hormone ethylene. The
nonripening phenotype of the dominant Green-ripe (Gr)
and Never-ripe 2 (Nr-2) mutants of tomato is the
result of reduced ethylene responsiveness in fruit tissues. In
addition, a subset of ethylene responses associated with floral
senescence, abscission, and root elongation are also impacted in
mutant plants, but to a lesser extent. Using positional cloning,
we have identified an identical 334-bp deletion in a gene of
unknown biochemical function at the Gr/Nr-2 locus.
Consistent with a dominant gain of function mutation, this
deletion causes ectopic expression of Gr/Nr-2, which in
turn leads to ripening inhibition. A CaMV35::GR
transgene recreates the Gr/Nr-2 mutant phenotype but does
not lead to a global reduction in ethylene responsiveness,
suggesting tissue-specific modulation of ethylene responses in
tomato. Gr/Nr-2 encodes an evolutionary conserved protein
of unknown biochemical function that we associate here with
ethylene signaling. Because Gr/Nr-2 has no sequence
homology with the previously described Nr (Never-ripe)
ethylene receptor of tomato we now refer to this gene only as
GR. Identification of GR expands the current
repertoire of ethylene signaling components in plants and
provides a tool for further elucidation of ethylene response
mechanisms and for controlling ethylene signal specificity in
crop plants.
Source:
http://www.pnas.org/cgi/content/abstract/0602319103v1?etoc
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