Interference between gerberin/parasorboside and carotenoid biosynthesis

Phytoene desaturase (PDS) plays a key role in the carotenoid biosynthesis in plants. Knocked-down the expression of PDS gene by virus induced gene silencing (VIGS) shows the photobleached phenotype in infected plants so that it has been used as a marker or a long time in VIGS systems with range of plant species. Tobacco rattle virus (TRV) based VIGS system, which uses PDS as the visual marker has been successfully applied and showed the white phenotype in Gerbera hybrida. However, 2-pyrone synthase (PS) gene, which encodes the first enzyme in gerebrin/parasorboside biosynthesis, is significantly reduced in these infected VIGS albino sectors. The transcription level of 2PS gene was also strongly suppressed in leaves treated with photobleaching herbicide, Norflurazon (NF), which inhibits the activity of PDS. Thus, down-regulation of 2PS gene in photobleaching sectors is caused by silencing PDS gene rather than by reacting of gerbera to TRV in VIGS treatment. Interestingly, expression of 2PS in transgenic tobacco (Nicotina tabacum SR1) causes photooxidative bleaching of the leaves. The reduction of ??-carotene in white leaves which analyzed by thin layer chromatograph (TLC) is the main reason; however, the interference between gerberin/parasorboside and carotenoid biosynthesis in these transgenic plants is still unclear. To overcome the effect of overexpression 2PS gene, exogenous mevalonic acid lactone (MAL) could be applied to partially rescue this transgenic phenotype at the seedling stages