15th International Conference on Arabidopsis Research - TAIR

T08-007
Novel proteins in the phloem of Brassicaceae.
Anna Kolasa(1), Patric Giavalisco(1), Kristin Kapitza(1), Julia Kehr(1)
1-Max Planck Institut of Molecular Plant Physiology, Department Willmitzer, Am Mühlenberg 1,
D-14424 Potsdam, Germany
Sieve element/ companion cell-complexes form the functional long distance
transport system, called phloem, in higher plants. This tissue is responsible
for the translocation of nutrients from the site of their synthesis to sink tissues
(i.e. developing leaves, flowers, roots). In addition, the phloem transport
stream contains proteins at reasonable concentrations. According to the fact
that mature sieve elements are not capable to transcribe and translate, it is
generally suggested that this specific set of proteins is synthesized in companion
cells and transported into their dependent sieve tubes via specialized
plasmodesmata. So far, there exists only limited information about the identity
and function of those proteins. Identification was hampered mainly by the limited
suitability of genetic model plants, like Arabidopsis, to sample sufficient
amounts of phloem sap.
In contrast, Brassica napus, a relative of Arabidopsis, allows the collection of
a sufficient amount of phloem sap to perform two-dimensional gel electrophoresis
(2D PAGE) and about 1000 soluble proteins can be separated using
this technique. To identify these proteins, visible spots are excised, digested
with trypsin and partially sequenced by ESI MS/MS.
As a complementary strategy, a cDNA expression library from complete RNA
of Brassica napus was created. This library was screened with antibodies
directed against total proteins from phloem exudate.
Both approaches led to the identification of a large set of formerly unknown
phloem sap proteins that should allow a deeper understanding of the vital
processes occurring inside this transport stream.
T08 Long Distance Transport (Signals Including Silencing and Metabolites)
T08-008
Functional analysis of the transcription factor TF55
Janina Lisso(1, 2), Yvonne Schmiele(1, 2), Ursula Uwer(3, 2), Thomas Altmann(1, 2)
1-Unversität Potsdam, Institut für Biochemie und Biologie -Genetik-, 14415 Potsdam
2-Max-Planck-Institut für Molekulare Pflanzenphysiologie, 14476 Golm
3-PlantTec Biotechnologie GmbH, 14473 Potsdam
Brassinosteroids (BRs) comprise a group of polyhydroxysteroids and
represent a recently identified class of phytohormones that show structural
similarities to steroid hormones of mammals and arthropods. They occur
ubiquitously in plants and control various developmental and metabolic processes
and are integrated into a complex regulatory network, which includes
several other plant hormones.
Several BR-biosynthetic mutants have hitherto been isolated including the
BR-deficient mutant dwarfs cbb1/dwf1/dim and cbb3/cpd as well as the
BR-insensitive cbb2/bri1.
In order to gain insight into the molecular mechanisms underlying BR action,
BR-regulated genes have been isolated by means of subtractive suppression
cDNA cloning.
Among approximately 200 clones checked about 20 proved to be differentially
expressed upon BR-treatment including cDNAs encoding OPR3, CAB,
Rubisco, RSZp22/21 protein, Retrovirus-like sequences, chloroplast-proteins
and several proteins of unknown function. The BR-inducible gene “TF55“
thus identified encodes a putative Zn- and RING-finger containing transcription
factor and has been chosen for detailed analysis. It is expressed in all
organs and the protein is supposedly located to the nucleus. It´s only homologue
in Arabidopsis is also expressed ubiquitousely throughout the plant but
is not BR-regulated.
Analysis of putative loss of function T-DNA insertion mutants of both genes
derived from the SIGnAL collection as well as of transgenic plants with altered
gene expression revealed no visible phenotypic alterations.
Affymetrix gene chip analysis conducted with k.o. mutants of “TF55” and
its homologue and with 35S::TF55 overexpressors suggest antagonistic
functions of both genes in stress and defense pathways.
15 th <strong>International</strong> <strong>Conference</strong> on Arabidopsis Research 2004 · Berlin