Plant Physiol, March 2002, Vol. 128, pp. 1098-1108
The Negatively Acting Factors EID1 and SPA1 Have Distinct
Functions in Phytochrome A-Specific Light
Signaling1
Yong-Chun
Zhou,
Monika
Dieterle,
Claudia
Büche, and
Thomas
Kretsch*
Albert-Ludwigs-Universität Freiburg, Institut für
Biologie 2/Botanik, Schänzlestrasse 1, D-79104 Freiburg,
Germany
EID1 (empfindlicher im dunkelroten Licht) and SPA1
(suppressor of phytochrome A[phyA]-105) function as negatively acting
components in phyA-specific light signaling. Mutants in the respective
genes led to very similar phenotypes under weak-light conditions. To examine whether both genes are functionally redundant, detailed physiological and genetic analyses were performed with
eid1 and spa1 mutants isolated from the
same wild-type background. Measurements of hypocotyl elongation,
anthocyanin accumulation, and Lhcb1-transcript accumulation under different light treatments demonstrated that SPA1
has a strong influence on the regulation of very low fluence responses
and a weaker influence on high-irradiance responses. In contrast, EID1
severely altered high-irradiance responses and caused almost no change
on very low fluence responses. Analyses on eid1 phyA-105
double mutants demonstrated that EID1 could not suppress the phenotype
of the weak phyA allele under continuous far-red light.
Measurements on eid1 spa1 double mutants exhibited a
strong interference of both genes in the regulation of hypocotyl elongation. These results indicate that EID1 and SPA1 are involved in
different but interacting phyA-dependent signal transduction chains.
1
This work was supported by the Deutsch
Forschungsgemeinschaft (grants "Signatransduktionsmutanten der
Photomorphogenese von Arabidopsis thaliana" to E. Schäfer and T.K.) and by the Graduiertenkolleg "Molekulare
Mechanismen der pflanzlichen Entwicklung."
*
Corresponding author; e-mail kretsch{at}uni-freiburg.de; fax
49-761-203-2612.
© 2002 American Society of Plant Physiologists