Evolution of the metabolic network leading to ascorbate synthesis and degradation using marchantia polymorpha as a model system

Abstract

In plants, l-ascorbic acid (AsA) is a functional enzyme cofactor, a major antioxidant, and a modulator of several biological processes including photosynthesis, photo-protection, cell wall growth and expansion, tolerance to environmental stresses, and synthesis of other molecules. One of the major roles of AsA in plants is detoxifying reactive oxygen species (ROS) such as singlet oxygen or peroxide radicals. ROS are produced when plants undergo biotic or abiotic stresses and if accumulated in high concentrations, can cause damage to macromolecules such as nucleic acids, membrane lipids, and proteins. Until now, little study has been done on ascorbate metabolism in liverworts. Bryophytes (liverworts, hornworts, and mosses) comprise the earliest diverging land plant lineages that came about approximately 360-450 million years ago between the Ordovician and Devonian periods. The ancient liverwort Marchantia polymorpha is an emergent model system specifically suited to use in the study of the evolution of different biosynthetic pathways. In this chapter, basal levels of both reduced and oxidized AsA in M. polymorpha are reported. Comparative and functional genomics experiments in combination with precursor feeding experiment are also discussed in order to provide valuable insights on the evolution of the AsA biosynthetic pathways.