Jasmonates: an update on biosynthesis, signal transduction and action in plant stress response, growth and development

Abstract

Background: Jasmonates are ubiquitously occurring lipid-derived compounds with signal functions in plant responses to abiotic and biotic stresses, as well as in plant growth and development. Jasmonic acid and its various metabolites are members of the oxylipin family. Many of them alter gene expression positively or negatively in a regulatory network with synergistic and antagonistic effects in relation to other plant hormones such as salicylate, auxin, ethylene and abscisic acid.

Scope: This review summarizes biosynthesis and signal transduction of jasmonates with emphasis on new findings in relation to enzymes, their crystal structure, new compounds detected in the oxylipin and jasmonate families, and newly found functions.

Conclusions: Crystal structure of enzymes in jasmonate biosynthesis, increasing number of jasmonate metabolites and newly identified components of the jasmonate signal-transduction pathway, including specifically acting transcription factors, have led to new insights into jasmonate action, but its receptor(s) is/are still missing, in contrast to all other plant hormones.

Fig. 1.

The 9-LOX and 13-LOX pathways, and JA biosynthesis (modified after Schilmiller and Howe, 2005; Wasternack, 2006).

Fig. 2.

Intracellular location of enzymes and intermediates in JA biosynthesis, illustrated on a SEM of a barley mesophyll cell showing the associated cellular compartments (photograph: B. Hause).

Fig. 3.

Structure–activity relationships among jasmonates. The various structural analogs and enantiomers were tested with respect to JA-induced gene expression in barley (data from Miersch et al., 1999b). ↓, decreased expression; ↑, increased expression; –, inactive; +, active in gene expression.

Fig. 4.

Metabolic fate of jasmonic acid. The carboxylic acid side-chain can be conjugated to the ethylene precursor 1-amino cyclopropane-1-carboxylic acid (ACC), methylated by JA methyl transferase (JMT), decarboxylated to cis-jasmone, conjugated to amino acids such as Ile by JA amino acid synthase (Arabidopsis, JAR1; tobacco, JAR4) or glucosylated. The pentenyl side-chain can be hydroxylated in positions C-11 or C-12. In the case of 12-OH-JA, glucosylation or sulfation are subsequent reactions. Reduction of the keto group of the pentenone ring can lead to cucurbic acid.

Fig. 5.

Local and systemic wound response in tomato and cell-type-specific occurrence of AOC, AOS and LOX (after Hause et al., 2003; modified from Wasternack et al., 2006).

Fig. 6.

Transcription factors involved in signalling pathways of JA and cross-talk to ethylene and SA (adapted from Pre, 2006, and Delker, 2007).

Fig. 7.

Root growth inhibition by 100 µm methyl jasmonate in wild-type (Col) and the JA-insensitive mutant coi1-16 (photograph: C. Delker).

Fig. 8.

The allene oxide cyclase (AOC) that establishes the correct enantiomeric structure of the cyclopentanone ring of jasmonate is encoded by a single copy gene in tomato, which is specifically expressed in ovules of young flower buds as revealed by AOC promoter activity tests (staining, left bottom) and immunocytological detection of AOC protein (black staining, right). The structure of jasmonic acid (bottom) and its precursor 12-oxophytodienoic acid (top) is shown.