Age-dependent wound induction of a myrosinase-associated protein from oilseed rape (Brassica napus)

In order to study the expression of the induced form of myrosinase-associat ed protein (iMyAP), a genomic clone encoding the protein was isolated from Brassica napus. The coding portion of the gene was found to consist of five exons separated by one long intron of 938 bp and three shorter introns of ca. 100 bp. A 1.9 kb promoter fragment including the 5'-untranslated region was cloned in front of the coding portion of the Escherichia coli iudA gen e and transformed into Arabidopsis thaliana. Expression was observed in hyp ocotyls of 4-day seedlings, but in 7-day seedlings the iMyAP promoter did n ot direct expression. In flowering plants, only the abscission zone of the young silique displayed promoter activity. In contrast, mechanical wounding of 7-day seedlings induced a systemic expression in all cells of the cotyl edons. Wounding of 14-day seedlings gave rise to systemic induced expressio n mainly in the vascular tissue. However, mechanical wounding and wounding by flea beetles (Phyllotreta undulata) of 4-week old plants only gave rise to a local induction of the promoter, suggesting that the systemic signal s ystem is age-dependent. Methyl jasmonate also induced iMyAP expression. In situ and northern analysis of iMyAP transcripts in young leaves of B. napus showed that the induction was high after 1 h and absent after 24 h. Compar ison of the effect of different types of wounding on the iMyAP promoter ind uction in transgenic Arabidopsis showed that similar degrees of local induc tion were achieved regardless of the degree of macerated tissue left on the plant.