Changes in Rosmarinic Acid Accumulation and Rosmarinic Acid Synthase Gene Expression in Thymus vulgaris L. Influenced by Phenology and Environmental Factors

Abstract

Thymus vulgaris L. is a commonly used medicinal and culinary plant. It tolerates drought well and contains biologically active polyphenols, among which is rosmarinic acid (RA). The last step of RA biosynthesis is catalyzed by rosmarinic acid synthase (RAS). Expression of the gene encoding for RAS was studied in garden thyme from the vegetative phase until the fruit-bearing phase. In addition, the effects of the temperature and water supply in a climatic chamber on the RAS gene expression and RA accumulation of the plants were studied. The RAS gene expression level decreased until the fruit-bearing phase, at which point it suddenly increased. The RA content and RAS gene expression fluctuated in a basically parallel manner in the climatic chamber, but some anomalies were found. Low (40%) soil water capacity increased the RA content compared to control plants. The highest RA content was 12.7% and the lowest was 0.9%. At cooler temperatures, no difference was found in the RA content of control and drought-stressed plants, whereas at a higher temperature, differences were detected. We found that warmer and drier conditions elevate the garden thyme's RA content and RAS gene expression, while the temperature alone does not affect these characteristics.