Hormone binding and signal transduction-- K.R.
BT - Plant Hormones: Biosynthesis, Signal Transduction, Action!
Since the first isolation of JAME as a constituent of the oil of Jasminum grandiflorum (), numerous jasmonate compounds have been detected in diverse plant phyla (). Jasmonates occur in algae, mosses, fungi, gymnosperms and angiosperms. The capacity to form or to convert various jasmonates is remarkably high in fungi; for example, more than 20 jasmonates were detected in culture filtrate of Fusarium oxysporum (, whilst Aspergillus niger grown on liquid medium could form more than 25 jasmonate compounds upon application of JA, 9,10-dihydro-JA and their methyl esters (). Some fungi, such as Botryodiplodia theobromae, are able to accumulate up to 500 µg mL−1 of culture medium of (+)-7-iso-JA, the initial product in JA biosynthesis (). Whereas in fungi the biological function of various jasmonates is unknown, application of jasmonates and their structural analogs to higher plants led to the first insights into their structural requirements for biological activity. Based on different assays, such as alkaloid formation (), tendril coiling (), tuber formation (), or gene expression (), the following structural requirements have been found ().
Plant Hormones: Biosynthesis, Signal Transduction, …
One of the best-studied signal-transduction pathways of jasmonates is that of wound-response, which was initially studied mainly in tomato. Briefly, a sequential action of the 18-aa peptide systemin, cleaved from prosystemin upon local wounding, activates JA biosynthetic enzymes such as AOC and leads to local rise in JA (). An amplification in JA formation has been suggested due to JA-dependent PROSYSTEMIN expression, a systemin-dependent AOC expression, and their common location in vascular bundles (; ). It is possible that JA acts as a systemic signal, leading also to systemic expression of genes encoding proteinase inhibitors (PINs) and other foliar compounds with negative effects on herbivore performance. Consequently the plant becomes immunized against a subsequent herbivore attack. Grafting experiments with JA-deficient and JA-signalling mutants in G. Howe's laboratory have shown that JA signalling – but not JA biosynthesis – is necessary in the systemic leaf. The numerous data on the wound response pathway have been reviewed repeatedly, including discussions on cross-talk to other signals, further elements of the wound-response pathway such as MAP kinases, and additional herbivore-induced compounds such as volatiles and their consequences for diverse plant–insect interactions, together with overlap to plant pathogen–interactions (, ; ; ). Here, I want to mention only few important new developments.