[Seminars] PSB event reminder
contact at psb.vib-ugent.be
contact at psb.vib-ugent.be
Thu Jun 23 09:10:01 CEST 2011
Calendar Name: seminars
Scheduled for: Thursday, June 23 2011, 11:00 - 12:30
Event text: Dr Hannele Tuominen
Umeå Plant Science Centre
Department of Plant Physiology
Umeå University
Umeå
SWEDEN
Details: Identification of novel regulators of lignification and
programmed cell death of xylem elements
ABSTRACT
Xylem maturation involves lignification and programmed
cell death (PCD) that are interlinked through the action
of the NAC family transcription factors. The downstream
regulators and the executioners are poorly known. We
have identified two metacaspase genes as candidates for
such key regulators in Populus trees on the basis of
specific upregulation during the xylem cell death phase
of wood formation. The closest Arabidopsis homologue to
these two Populus genes is METACASPASE9 (AtMC9,
At5g04200). Also AtMC9 shows xylem specific expression
pattern throughout the plant, suggesting involvement in
xylem cell death. In order to characterise the function
of AtMC9 in xylem development, a reverse genetic
approach was taken in Arabidopsis. AtMC9 T-DNA knock-out
lines showed rather normal progression of protoxylem
differentiation and PCD in in vitro grown seedling roots
by analysis of genetic crosses to various xylem reporter
lines. Interestingly, AtMC9 RNAi lines revealed
increased overall growth of the plants, which together
with double mutant analyses in the metacaspase family
suggest involvement of AtMC9 together with other type II
metacaspase genes in growth control. We are currently
performing proteomic analyses to identify targets of the
AtMC9 action. Upstream regulators have been sought by
screening an EMS mutagenised proAtMC9::GFP reporter
line.
We have also utilized the Zinnia elegans in vitro
tracheary element (TE) differentiation system to
identify novel regulators of lignification and PCD. In
this system, application of silver thiosulphate (STS)
blocked both lignification and PCD of TEs resulting in
prolonged lifespan of the TEs, while TE secondary
cellulose formation was not affected. This allowed us to
identify novel genes specifically involved in
lignification and/or PCD by analyzing differential gene
expression patterns between cell cultures treated with
or without STS. One of the identified genes was a PIRIN
gene that was previously implicated in transcriptional
regulation in mammals. Expression of the Zinnia PIRIN
gene was strongly upregulated during lignification
and/or PCD of normally developing TEs, whereas no
upregulation was present in non-lignifying TEs after STS
treatment. Functional analysis of the PIRIN gene family
was undertaken in Arabidopsis thaliana which contains
four PIRIN (PRN) homologs: AtPRN1 (At3g59220), AtPRN2
(At2g43120), AtPRN3 (At3g59260) and AtPRN4 (At1g50590).
Promoter activity assay by using GUS reporter gene
showed that, out of the four PIRIN genes, AtPRN2 was
most specifically expressed in the vascular tissues.
Pyrolysis-GC/MS analysis of the various PIRIN gene
family mutants suggests involvement of AtPRN2 in control
of lignification. However, in vitro and in vivo analyses
demonstrated interaction of AtPRN2 with several
different types of proteases, which suggests involvement
of AtPRN2 primarily in regulation of hydrolytic
processes during xylem cell death. We can therefore link
together the two processes of lignification and PCD and
provide evidence on a novel player in this interplay.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: https://maillist.psb.ugent.be/mailman/private/seminars/attachments/20110623/36f6e001/attachment.html
More information about the Seminars
mailing list