Transcript profile of transgenicArabidopsis constitutively producing methyl jasmonate

Abstract

Using an Affymetrix GeneChip | containing 8300 oligonucleotide probes, we measured transcript levels in transgenic Arabidopsis overexpressing the jasmonate carboxyl methyltransferase gene (AtJMT). When compared with wild-type plants, 5-week-old transgenics exhibited significant alterations (more than a two-fold increase or decrease) in the expression levels of 168 genes. Among them, 80 were up-regulated, including those involved in defense, oxidative stress-tolerance, and senescence. In contrast, the expression of 88 genes, including those that function in photosynthesis and cold/drought-stress responses, was significantly down-regulated. Thus, endogenous generation of methyl jasmonate through AtJMT-overexpression modified the transcript levels of genes previously identified as being jasmonate-responsive. This result confirms that MeJA formation is a key control point for jasmonate-responsive gene expression in plants.

Constitutive expression of methyl jasmonate-inducible responses delays reproduction and constrains fitness responses to nutrients in Arabidopsis thaliana

“…For example, it is well known that exogenous jasmonate treatment decreases root length in Arabidopsis, and it lowers photosynthetic rates in a number of species (Staswick et al 1992;Metodiev et al 1996). These traits have not been examined in JMT plants, but some jasmonate-mediated responses that are altered in JMT plants include reduced expression of several photosynthesis-associated genes (Jung et al 2007). Such effects are all part of the costs of methyl jasmonate overproduction and may physiologically constrain the ability of JMT plants to fully respond to increases in soil nutrient availability.…”

“…Recently, a gene that mediates growth suppression by jasmonate in Arabidopsis was identified (Yan et al 2007). This discovery indicates that some of the ''costs'' of defense production may not only be due to passive resource constraints of defense production on growth, but instead are part of an adaptive program by induced plants to divert resources away from certain aspects of growth toward defense production (Hermsmeier et al 2001;Jung et al 2007). Length of the three largest siliques was greater in JMT plants overall, but it was increased by fertilization in a similar fashion in both genotypes; the only trait in which phenotypic responses to nutrients did not vary among genotypes.…”

“…Briefly, JMT plants have been transformed to overexpress Sadenosyl-L-methionine: jasmonic acid carboxyl methyltransferase (JMT), which specifically methylates jasmonic acid (Seo et al 2001;Schaller et al 2005). As a consequence, JMT plants constitutively produce threefold higher methyl jasmonate and twofold higher total jasmonate levels in their leaves than wild-type plants (Seo et al 2001), and exhibit constitutively elevated methyl-jasmonate responsive genes in their leaves, including defensins, various PR proteins, and oxidative stress related genes (Seo et al 2001;Jung et al 2003Jung et al , 2007. In turn, JMT plants are more resistant than wild-type plants or vector controls to attack by the fungus Botrytis cinerea (Seo et al 2001), the bacterium Pseudomonas syringae pv.…”

Signaling pathways for the Biosynthesis and action of Jasmonates

“…The mutual, antagonistic interaction between the ABA and JA/ethylene signaling pathways has also been found with defense-gene expression and disease resistance (Anderson et al, 2004). Recent microarray analyses have shown that external treatment (Jung et al, 2007a) or endogenous overproduction of MeJA (Jung et al, 2007b) significantly reduces the transcription of abscisic acidresponsive cold/drought-stress genes in Arabidopsis.…”

“…In contrast, genes involved in photosynthesis, such as ribulose bisphosphate carboxylase/oxygenase (Rubisco), chlorophyll a/bbinding protein, and light-harvesting complex II, are downregulated. Transgenic Arabidopsis producing an excess of endogenous MeJA constitutively expresses numerous jasmonate-responsive genes in the absence of wounding or jasmonate treatment (Seo et al, 2001 ;Jung et al, 2007b).…”