Promotion of nicotine biosynthesis in transgenic tobacco by overexpressing allene oxide cyclase from Hyoscyamus niger.

Plant secondary metabolites are a wide variety of low-molecular weight compounds whose productions are often enhanced in response to both biotic and abiotic stresses. Many of the responses are mediated by a class of hormones, named as jasmonates. In jasmonate biosynthetic pathway of plants, allene oxide cyclase (AOC, EC 5.3.99.6) catalyzes the most crucial step. Here a heterologous AOC gene from Hyoscyamus niger L. (black henbane), named HnAOC (GenBank accession No. AY708383), was overexpressed in Nicotiana tabacum cv. Petit Havana to investigate the consequence on nicotine content. This study revealed that the transcription of HnAOC in tobacco resulted in overexpression of nicotine biosynthetic pathway genes and higher yield of nicotine, with the maximum of 4.8-fold over control. Therefore, it indicated that without the cost of extrinsic hormones, genetic manipulation of jasmonate biosynthetic pathway genes could be an alternative approach in metabolic engineering for the production of valuable secondary metabolites, which were induced by jasmonates.