Expression analysis of zeaxanthin epoxidase of genetically engineered zeaxanthin-rich potatoes in comparison to conventional cultivars under field conditions

Two genetically engineered (GE) zeaxanthin-rich potato (Solanum tuberosum L.) clones, derived from potato cultivar ‘Baltica’ were evaluated under open-field conditions with respect to agronomic performance, stability and tuber-specific expression of the inserted zeaxanthin epoxidase (zep) gene. Data collected from two field sites totalling four environments in Germany demonstrated that general morphology and tuber yield of GE potato clones were not impaired by the metabolic changes in tuber tissue. Quantitative real-time PCR analysis of zep gene expression in leaves, roots and tubers collected at three different developmental stages from the two GE potato clones and the conventional counterpart clone ‘Baltica’ showed that the transgene maintained its ability to induce the accumulation of zeaxanthin in tubers, while no significant zep expression changes were found in leaves and roots. The results clearly demonstrated that the tuber-specific promoter led to a strict tissue-specific expression of the inserted gene in the two GE potato clones in each of the four environ-ments. Additionally, HPLC measurement showed that the tubers from two GE clones contained 19.5 to 58.7 μg/g dw of zeaxanthin, while the zeaxanthin content in the tubers of ‘Baltica’ was under detection level. HPLC results together with qRT-PCR results confirmed the inverse relationship between zep expression level and the accumulation of zeaxanthin in GE tubers. Furthermore, zep expression analysis of four other conventional cultivars showed that gene expression differed in a similar or even greater range among the four conventional cultivars investigated than the variation between GE clones and ‘Baltica’. ___________________________________________________________