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Plant Physiol, January 2002, Vol. 128, pp. 173-181
Brassinosteroid Mutants Uncover Fine Tuning of Phytochrome
Signaling1
Laura G.
Luccioni,2
Karina A.
Oliverio,2
Marcelo J.
Yanovsky,3
Hernán E.
Boccalandro, and
Jorge J.
Casal*
IFEVA, Faculty of Agronomy, University of Buenos Aires and National
Research Council, Av. San Martín 4453, 1417 Buenos
Aires, Argentina
Phytochromes (phy) A and B provide higher plants the ability
to perceive divergent light signals. phyB mediates red/far-red light
reversible, low fluence responses (LFR). phyA mediates both very-low-fluence responses (VLFR), which saturate with single or
infrequent light pulses of very low fluence, and high irradiance responses (HIR), which require sustained activation with far-red light.
We investigated whether VLFR, LFR, and HIR are genetically coregulated.
The Arabidopsis enhanced very-low-fluence response1 mutant, obtained in a novel screening under hourly far-red light pulses, showed enhanced VLFR of hypocotyl growth inhibition, cotyledon unfolding, blocking of greening, and anthocyanin synthesis. However, eve1 showed reduced LFR and HIR. eve1 was
found allelic to the brassinosteroid biosynthesis mutant
dim/dwarf1. The analysis of both the brassinosteroid
mutant det2 in the Columbia background (where VLFR are
repressed) and the phyA eve1 double mutant indicates that the negative effect of brassinosteroid mutations on LFR requires phyA signaling in the VLFR mode but not the expression of the VLFR.
Under sunlight, hypocotyl growth of eve1 showed little
difference with the wild type but failed to respond to canopy
shadelight. We propose that the opposite regulation of VLFR versus LFR
and HIR could be part of a context-dependent mechanism of adjustment of
sensitivity to light signals.
1
This work was supported by the Fondo
Nacional de Ciencia y Técnica (grant no. BID 1201/OC-AR-PICT
06739), the University of Buenos Aires (grant no. TG59), and the
Fundación Antorchas (grant no. A-13622/1-40).
2
These two authors contributed equally to the paper.
3
Present address: Department of Cell Biology, The Scripps
Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037.
*
Corresponding author; e-mail casal{at}ifeva.edu.ar; fax
5411-4514-8730.
© 2002 American Society of Plant Physiologists
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