Silencing of the Phytoene desaturase gene mitigates oxidative stress through the accumulation of free amino acids

Abstract

Phytoene desaturase (PDS) is a rate-limiting enzyme involved in the biosynthesis of carotenoids, which converts phytoene to zeta-carotene in a two-step desaturation reaction. Transiently blocked carotenogenesis by silencing the PDS gene in Nicotiana benthamiana (NbPDS) using the virus-induced gene silencing (VIGS) technique was used. Silencing of NbPDS induced dwarfism and an albino-type leaf trait in N. benthamiana. The NbPDS-silenced leaves accumulated free amino acids in amounts 9.5-folds greater than those of the GFP-silenced control leaves, but contained only 59.6% of total soluble proteins. When treatment with 10 and 100 μM paraquat was carried out to induce oxidative stress, NbPDS-silenced N. benthamiana demonstrated more resistance at both concentrations compared to the control plants. These data strongly suggest that high concentrations of free amino acids occur because they are inadequately incorporated into proteins of the NbPDS-silenced plants, but reduce injury inflicted by oxidative stress even without the assistance of important antioxidants like carotenoids.