Genetic manipulation of carotenoid biosynthesis and photoprotection

There are multiple complementary and redundant mechanisms to provide protection against photo-oxidative damage, including non-photochemical quenching (NPQ). NPO dissipates excess excitation energy as heat by using xanthophylls in combination with changes to the light-harvesting complex (LHC) antenna. The xanthophylls are oxygenated carotenoids that in addition to contributing to NPQ can quench singlet or triplet chlorophyll and are necessary for the assembly and stability of the antenna. We have genetically manipulated the expression of the ε-cyclase and β-carotene hydroxylase carotenoid biosynthetic enzymes in Arabidopsis thaliana. The ε-cyclase over-expression confirmed that lut2 (lutein deficient) is a mutation in the ε-cyclase gene and demonstrated that lutein content can be altered at the level of mRNA abundance with levels ranging from 0 to 180% of wild-type. Also, it is clear that lutein affects the induction and extent of NPQ. The deleterious effects of lutein deficiency on NPQ in Arabidopsis and Chlamydomonas are additive, no matter what the genetic background, whether npq1 (zeaxanthin deficient), aba1 or antisense β-hydroxylase (xanthophyll cycle pool decreased). Additionally, increasing lutein content causes a marginal, but significant, increase in the rate of induction of NPQ despite a reduction in the xanthophyll cycle pool size.