15th International Conference on Arabidopsis Research - TAIR

T08-009
C8 GIPK, a GAI-interacting protein kinase that
controls hypocotyl elongation in Arabidopsis
Hanbing Li(1), Melina Zourelidou(1), Carola Kuhnle(1), Claus Schwechheimer(1)
1-Zentrum für Molekularbiologie der Pflanzen(ZMBP) - Center for Plant Molecular Biology, Abteilung
Entwicklungsgenetik, Auf der Morgenstelle 5, D - 72076 Tuebingen, Germany
Gibberellic acid (GA) regulates a variety of plant developmental processes
including germination and elongation. In Arabidopsis thaliana, several
downstream players of GA signaling have been described, the best known
of which are the DELLA proteins. These proteins are highly conserved and
thought to act as repressors of GA signaling. GAI and RGA, two members of
the DELLA protein family, have been implicated in mediating hypocotyl and
stem elongation. Here, we report on the trans-membrane receptor protein
kinase C8 GIPK. C8 GIPK is an active protein kinase that interacts in the
yeast two-hybrid system with GAI and RGA. Confocal microscopy analyses
demonstrate that C8 GIPK is localized to the plasma membrane. C8 GIPK
antisense lines germinate faster than the wildtype. Moreover, hypocotyl and
stem elongation are increased. Based on our results, we believe that C8 GIPK
is a negative regulator of GA-mediated processes.
15 th <strong>International</strong> <strong>Conference</strong> on Arabidopsis Research 2004 · Berlin
T08-010
Essential role of riboflavin pathway in jasmonate
signaling
Shi Xiao(1), Liangying Dai(1), Fuquan Liu(1), Zhilong Wang(1), Wen Peng(1), Daoxin
Xie(1)
1-Laboratory of Plant Signal Transduction, Institute of Molecular and Cell Biology, 30 Medical
Drive, 117609 Republic of Singapore (Email: daoxin@imcb.a-star.edu.sg)
The Arabidopsis coi1 mutation defined a key regulator in the JA signaling
pathway. The recessive coi1 mutants fail to respond to jasmonate and coronatine,
a phytotoxin structurally similar to jasmonic acid, displaying defects in
JA-regulated gene expression, exhibiting male sterility and showing susceptibility
to insects attack and pathogens infection. The COI1 gene encodes a
592-amino acid protein containing an F-box motif and 16 leucine rich repeat
sequences (LRRs), which interact with Arabidopsis CULLIN1, RBX1 and Skp1
like proteins ASK1 or ASK2 to assemble SCFCOI1 complexes in planta. The
SCFCOI1 is assumed to regulate the abundance of the substrate proteins,
which may suppress a set of transcription factors and/or affect the expression
of appropriate target genes essential for JA responses.
To better understand the molecular mechanism via which COI1 regulates JA
responses, we conducted a screen for suppressors of the coi1 mutant. A
cos1 (coi1 suppressor 1) recessive mutant was identified and found to regain
wild type-like phenotypes of JA-sensitive root elongation, gene expression,
senescence and defense response in the coi1 background (Xiao et al 2004).
The COS1 gene was cloned using map-based approach and found to encode
a lumazine synthase, a key component in riboflavin pathway that is essential
for diverse yet critical cellular processes. The riboflavin pathway is speculated
to act downstream of COI1 and to be required for suppression of the COI1mediated
root growth, senescence and plant defense.
Xiao, S., Dai, L., Liu, L., Wang,Z., Peng, W., and D Xie. (2004) Plant Cell 16:1132-1142
T08 Long Distance Transport (Signals Including Silencing and Metabolites)