15th International Conference on Arabidopsis Research - TAIR

T02-019
Modulation of light (phytochrome B) signal
transduction by the response regulator ARR4
Gabi Fiene(1), Virtudes Mira-Rodado(1, 2), Uta Sweere(1, 2), Eberhard Schäfer(2),
Klaus Harter(1)
1-Botanisches Institut, Universität zu Köln, Gyrhofstr. 15, D-50931 Köln
2-Institut für Biologie II, Albert-Ludwigs-Universität Freiburg, Schänzlestraße 1, D-79104 Freiburg
Within the last years it became evident that the canonical elements of His-to-
Asp two-component signaling pathways are conserved in higher plants and
play a crucial role in hormone and light signalling as well as in developmental
processes (Grefen and Harter, 2004).
During our recent studies we characterized in detail the molecular function
of the Arabidopsis A-type response regulator ARR4. ARR4 interacts with the
extreme NH2-terminus of the red light photoreceptor phytochrome B (phyB),
thereby stabilizes the active Pfr form of phyB under inductive and continuous
light conditions and elevates the level of phyB-Pfr in planta. In agreement
with these observations overexpression of wildtype ARR4 results in plants hypersensitive
to red light. Mutation of the conserved Asp95 to Asn creates an
ARR4 version (ARR4D95N) which could not longer be phosphorylated in vitro,
but still interacts with phyB in vivo, and confers red light hyposensitivity and
a phyB mutant-like phenotype in transgenic Arabidopsis plants. These results
indicate that the function of ARR4 on phyB depends on its phosphorylation
state. Further data will be presented suggesting that ARR4 phosphorylation
and activity is regulated by a hormone-driven two-component signalling
cascade. In summary, we propose a working model, in which ARR4 acts
as an output element of a two-component system that modulates red light
signalling and the light responsiveness of Arabidopsis directly on the level of
phyB dynamics.
Grefen C, Harter K (2004) Plant two-component systems:principles, function, complexity and cross
talk PLANTA in revision
T02 Development 2 (Shoot, Root)
T02-020
Growth control of the Arabidopsis root meristem by
Cytokinin.
Raffaele Dello Ioio(1), Alessandro Busetti(1), Paolo Costantino(2), Sabrina
Sabatini(1, 2)
1-Laboratories of Functional Genomics and Proteomics of Model Organisms
2-1 Department of Genetics and Molecular Biology, "La Sapienza" University, P.le A. Moro 5, 0018
Roma, Italy
Two plant hormones, auxins and cytokinins, have long been recognized as
essential signaling molecules in diverse processes of plant growth and development.
They are believed to act synergistically or antagonistically to control
fundamental developmental process such as cell division and cell differentiation
which ultimately lead to shoot and root organogenesis. Although, molecular,
genetic and biochemical studies have already provided evidence for
a role of auxin in controlling cell specification, cell division and cell polarity,
the role of cytokinin at the cellular and tissue level during plant development
has remained elusive. Recently a number of molecular and genetic tools have
been developed to study cytokinin signal transduction pathway in Arabidopsis.
We will take advantage of these tools to shed light on the role of cytokinin
in planta by focusing on the well-characterized Arabidopsis root meristem.
15 th <strong>International</strong> <strong>Conference</strong> on Arabidopsis Research 2004 · Berlin