The role of alpha-tocopherol in the protection of tomato plants against abiotic stress

The ability of energy conversion by the photosynthetic machinery under stress and its

capacity to adjust to an ever-changing environment is crucial for plant survival. The

photosynthetic light reactions occur at the photosystems in the thylakoids of chloroplasts.

The photosystems are composed of proteins in a specific lipid environment. It includes

not only membrane lipids but also lipophilic pigments (chlorophylls, carotenoids) and

prenylquinones (plastoquinone, phylloquinone, tocopherol). Apart from their respective

roles in light harvesting and electron transport, carotenoids and prenylquinones have

important antioxidant properties and protect plant cells against reactive oxygen species.

The focus of this work is to understand how plants resist and adapt to environmental

stress in particular high light, high temperature and the combination of the two. Lipid

metabolism takes places in plastid subcompartments, at the level of envelopes, at thylakoid

microdomains called plastoglobules. Plastoglobules are involved in various essential

biosynthetic metabolic pathways and accumulation of prenylquinone molecules. In this

thesis, we use tomato as the model system to address the role of (prenyl) lipids synthesis

and remodelling to protect photosynthetic function under stress. After an introduction

on the implication of photosynthetic machinery in lipid metabolism, in Chapter 2 we

summarized recent advances in plastoglobule research and their findings on biosynthesis

and metabolism of Vitamins E and K1. Then in Chapter 3, we investigate the question

of how the photosynthetic machinery is protected against heat stress. Amongst many

hundreds of compounds that change under heat stress, we identified a-tocopherol and

plastoquinone as the most significantly increased antioxidants. This finding suggests a

new role for these two prenylquinones in protecting the photosynthetic apparatus against

temperature stress. In Chapter 4, through a joint effort, we provided valuable information

on the metabolic fluxes and biosynthesis of Vitamin E in tomato. Finally, in Chapter 5, we

intended to identify molecules that contribute to the protection against combined high

temperature and high light stress. To perturb a-tocopherol levels we used the tomato vte5

knock down-line. The data indicate that VTE5 protects against combined high light and

high temperature stress and does so by supporting a-tocopherol production.Overall, this thesis contributes to a better understanding of the role of prenylquinone compounds, in

the resistance of tomato plants against high light and high temperature stresses.