Analysis of wound-induced gene expression in Nicotiana species with contrasting alkaloid profiles.

Abstract

We determined the capacity of three Nicotiana (Solanaceae) species with very different alkaloid profiles (Nicotiana sylvestris Speg & Comes, Nicotiana alata Link & Otto and Nicotiana glauca Grah.) to increase their alkaloid contents in both leaf and root tissues following foliage damage. We also investigated the transcriptional responses of genes encoding enzymes important for alkaloid biosynthesis, namely quinolinate phosphoribosyltransferase (QPT), putrescine N-methyltransferase (PMT), ornithine decarboxylase (ODC) and the putative alkaloid biosynthetic gene A622. In response to wounding of foliage in the well studied 'model' species N. sylvestris, a rise, approximately 2-fold, in leaf nicotine levels was observed several days after a 4-5-fold increase in the transcript levels of all genes in the roots. In contrast, leaf tissues of the ornamental tobacco N. alata showed very low levels of any pyridine alkaloid, even when analysed 1 week after wounding, correlating with a general lack of transcript abundance representing any of these genes in leaves or roots following foliage damage. However, addition of methyl jasmonate to cultured roots of N. alata did produce elevated levels of nicotine and anatabine raising the possibility that components of the leaf-root wound signalling system in N. alata are different from those in N. sylvestris. Wounding of the tree tobacco N. glauca, was followed by a 2-fold increase in anabasine levels several days later. This increase followed a large rise in transcript levels of ODC, QPT and A622, though not PMT, in wounded leaves, but not in non-wounded leaves or roots. These data support the hypothesis that N. glauca is able to produce increased anabasine levels following wounding in its foliage, setting it apart from N. sylvestris where induced alkaloid production takes place in roots. We discuss the possibility that increased transcript levels detected by ODC and A622 probes play important roles in anabasine synthesis in N. glauca.