New weapons and a rapid response against insect attack - PubMed (original) (raw)

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New weapons and a rapid response against insect attack

John Browse et al. Plant Physiol. 2008 Mar.

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Figure 1.

Figure 1.

Biosynthesis and metabolism of JA. The octadecanoid pathway converts 18:3 to (+)-7-_iso_-JA, which epimerizes to the more stable (−)-JA isomer. It is generally assumed that (+)-7-_iso_-JA is the biologically relevant and more active form of the hormone. JA is metabolized to a wide range of derivatives (see text for details). For example, JA carboxyl methyltransferase (JMT in the image) converts JA to the volatile compound MeJA. Conjugation of JA to Ile by JAR1 produces JA-Ile, which promotes COI1 interaction with the JAZ1 repressor protein. Other enzymes, presumably related to JAR1, catalyze the formation of other JA-amino acid conjugates (JACs in the image). Coronatine (in red) is a phytotoxin produced by virulent strains of Pseudomonas syringae. The toxin functions as a JA mimic and is structurally related to JA-Ile.

Figure 2.

Figure 2.

Model of JA signaling in response to herbivore attack. A, Low intracellular levels of JA-Ile (green stars) favor the accumulation of JAZ proteins, which repress the activity of transcription factors (TF in the image) such as MYC2 that positively regulate JA-responsive genes. B, Tissue injury caused by insect herbivores results in rapid accumulation of bioactive JAs, which promote SCFCOI1-mediated ubiquitination and subsequent degradation of JAZ proteins via the 26S proteasome. JA-induced removal of JAZ proteins causes derepression of TF and the activation of early response genes. Although this model depicts JA-Ile as the active signal for triggering JAZ degradation, current evidence does not exclude the possibility that other JAs are also active. See text for more details.

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