Transcript posterexample2

In Arabidopsis thaliana, the atToc132 and atToc120 receptor complex does represent the critical regulatory
point in the biosynthesis of jasmonic acid
Meshack Afitlhile, Danielle Sprout, Samantha Workman, Sue-Hum Musser, Michelle Golz, Gilles Kouassi
Department of Biological Sciences, Western Illinois University
When plants are challenged by insect herbivores or
mechanically wounded, the linolenic acid (18:3)
derived plant hormone, jasmonic acid (JA) is
synthesized and accumulates to levels, which are 10 to
20-fold higher than basal levels. The JA pathway is
initiated in the chloroplasts and completed in the
peroxisomes. JA is then exported to the cytoplasm
where it is conjugated to isoleucine to form JA-Ile,
which binds to its receptor and induce the signal that
turns on array of defense genes , including plant
defensin, PDF1.2. Enzymes that function in the JA
pathway are nuclear-encoded and synthesized in the
cytoplasm, and are imported into the chloroplasts.
The chloroplast outer membrane has receptor
complexes that consist of Toc33/34, Toc75 and either
Toc 159 or Toc132/120. These receptor complexes
bind pre-proteins and directs them into Toc75
channel. The intermembrane space protein, Tic22
binds and directs the emerging pre-proteins to
Tic20/21 channel in the inner membrane, and the
imported proteins are processed in the stroma. The
atToc159 receptor is specific for the import of lightinduced proteins, while atToc132/120 are redundant
receptors that imports housekeeping proteins.
To measure the expression
of genes that encode
enzymes that function in the
JA pathway. We also
measured the expression of
a gene that is induced by
elevated levels of jasmonic
acid.
Hypothesis
We propose that atToc132 and
atToc120 receptor complex is
the major route in the import of
LOX-2, AOS and AOC, which
are enzymes that function in
the initial steps of the JA
pathway. We expect a wounded
mutant to accumulate reduced
levels of mRNA that encode
LOX-2, AOS, OPR-3, and the
JA responsive gene, PDF1.2.
Wt, uw
5
Wt, w
4
Mt, uw
3
Mt, w
2
1
0
LOX-2
AOS
OPR-3
Figure 1. Expression of LOX-2, AOS and OPR3 genes in the unwouded and
wounded leaves of atToc132/120 mutant and wild type plants. Data represent
the mean ± SEM of 4 replicates.
5
Discussion
The unwounded leaves of both wild type and mutant had low expression levels of
lipoxygease 2, allene oxide synthase, OPDA reductase 3 and low induction of the JA
responsive gene, PDF1.2. The JAZ1 gene that encodes for a protein that repress genes in
the JA pathway was elevated in the unwounded tissues of both wild type and mutant. As
expected, in the wounded wild type the expression of genes in the JA pathway and JAinduced gene PDF1.2 was increased. In the wounded mutant however, expression of LOX-2,
AOS and OPR-3 remained low. The expression of PDF1.2 gene remained at basal level in
the wounded mutant. This observation suggests that in the mutant, JA or JA-Ile did not
accumulate to levels high enough to induce the expression of PDF1.2 gene. Our data indicate
that atToc132/120 receptor complex is required for JA synthesis, and most likely this
receptor complex plays an important role in the import of LOX-2, AOS and the cyclase.
6
Relative fold change
Objective
Relative fold change
Introduction
Acknowledgments
Wt, uw
Wt, w
4
Mt, uw
3
Mt, w
2
1
0
PDF1.2
Paul Jarvis (Univ. of Leicester,
UK) for a gift of mutant seeds.
JAZ1
Figure 2. Expression of PDF1.2 and JAZ1 genes in the unwouded and wounded
leaves of atToc132/120 mutant and wild type plants. Data represent the mean ±
SEM of 4 replicates.