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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. 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 light-induced proteins, while atToc132/120 are redundant receptors that imports housekeeping proteins. Introduction 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. Objective Hypothesis 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. 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 JA-induced 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 Discussion Paul Jarvis (Univ. of Leicester, UK) for a gift of mutant seeds. Acknowledgments 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. In Arabidopsis thaliana, the atToc132 and atToc120 receptor complex does represent the critical regulatory point in the biosynthesis of jasmonic acid

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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 - PowerPoint PPT Presentation

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Meshack Afitlhile, Danielle Sprout, Samantha Workman, Sue-Hum Musser, Michelle Golz, Gilles KouassiDepartment 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 light-induced proteins, while atToc132/120 are redundant receptors that imports housekeeping proteins.

Introduction

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.

Objective Hypothesis

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.

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 JA-induced 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.

Discussion

Paul Jarvis (Univ. of Leicester, UK) for a gift of mutant seeds.

Acknowledgments

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.

In Arabidopsis thaliana, the atToc132 and atToc120 receptor complex does represent the critical regulatory point in the biosynthesis of jasmonic acid

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