Phenylalanine ammonia-lyase (PAL) gene activity in response to proline and tyrosine in rosemary callus culture
Phenylalanine ammonia-lyase (PAL) catalyzes the biosynthesis of rosmarinic acid (RA), tyrosine and phenylalanine are the precursors of RA, while proline drives metabolite precursors toward Shikimate and phenylpropanoid pathway ending with the production of RA. The aim of this study was to investigate the PAL gene activity in the callus of rosemary (Rosmarinus officinalis) due to exogenous application of L-proline and L-tyrosine. Four different concentrations of L-proline and L-tyrosine (0, 4, 5 and 6 mM, and 0, 0.4, 0.6 and 0.8 gm/L) respectively, were added to the basal Murashige and Skoog (MS) medium. The expression of the PAL gene was investigated and compared with the callus RA production. It was found that RA production increased significantly at low proline application (4 mM), on the other hand, tyrosine application at low concentrations had no effect on RA accumulation, while high tyrosine concentration (0.8 g/L) increased RA accumulation. When comparing PAL gene activity and RA production in callus tissues, it was found that they were correlated. Proline application alone at 4 mM or tyrosine alone at 0.8 g/L enhanced PAL gene activity, and also combining both proline at 4 mM and tyrosine at 0.8 g/L enhanced PAL gene activity and produced the highest RA accumulation in callus tissues [0.047 mg/g freash weight (fw)].
Key words: Phenylalanine ammonia-lyase (PAL), gene expression, rosmarinic acid, Rosmarinus officinalis, tyrosine, proline.