Metabolism and Regulatory Functions of O-Acetylserine, S-Adenosylmethionine, Homocysteine, and Serine in Plant Development and Environmental Responses.

Mutsumi Watanabe,Masami Yokota Hirai,Yukako Chiba

doi:10.3389/fpls.2021.643403

Abstract

The metabolism of an organism is closely related to both its internal and external environments. Metabolites can act as signal molecules that regulate the functions of genes and proteins, reflecting the status of these environments. This review discusses the metabolism and regulatory functions of O-acetylserine (OAS), S-adenosylmethionine (AdoMet), homocysteine (Hcy), and serine (Ser), which are key metabolites related to sulfur (S)-containing amino acids in plant metabolic networks, in comparison to microbial and animal metabolism. Plants are photosynthetic auxotrophs that have evolved a specific metabolic network different from those in other living organisms. Although amino acids are the building blocks of proteins and common metabolites in all living organisms, their metabolism and regulation in plants have specific features that differ from those in animals and bacteria. In plants, cysteine (Cys), an S-containing amino acid, is synthesized from sulfide and OAS derived from Ser. Methionine (Met), another S-containing amino acid, is also closely related to Ser metabolism because of its thiomethyl moiety. Its S atom is derived from Cys and its methyl group from folates, which are involved in one-carbon metabolism with Ser. One-carbon metabolism is also involved in the biosynthesis of AdoMet, which serves as a methyl donor in the methylation reactions of various biomolecules. Ser is synthesized in three pathways: the phosphorylated pathway found in all organisms and the glycolate and the glycerate pathways, which are specific to plants. Ser metabolism is not only important in Ser supply but also involved in many other functions. Among the metabolites in this network, OAS is known to function as a signal molecule to regulate the expression of OAS gene clusters in response to environmental factors. AdoMet regulates amino acid metabolism at enzymatic and translational levels and regulates gene expression as methyl donor in the DNA and histone methylation or after conversion into bioactive molecules such as polyamine and ethylene. Hcy is involved in Met–AdoMet metabolism and can regulate Ser biosynthesis at an enzymatic level. Ser metabolism is involved in development and stress responses. This review aims to summarize the metabolism and regulatory functions of OAS, AdoMet, Hcy, and Ser and compare the available knowledge for plants with that for animals and bacteria and propose a future perspective on plant research.

Highlights

METABOLISM INVOLVING OAS, ADOMET, HCY, AND SERPlants are photosynthetic auxotrophs that assimilate carbon dioxide and inorganic ions absorbed from the soil into organic compounds
We summarized the metabolism of S-containing amino acids and related compounds and the C1 metabolism in plants, focusing on regulatory function of AdoMet, OAS, Hcy, and Ser, in comparison with those in bacteria and animals
The regulation of protein subcellular localization, which might be realized by translational regulation, is the issue we should tackle

Summary

Introduction

Plants (land plants) are photosynthetic auxotrophs that assimilate carbon dioxide and inorganic ions absorbed from the soil into organic compounds. They share common biosynthetic pathways for proteinogenic amino acids with prokaryotic microbes such as Escherichia coli. Plant metabolism is compartmentalized into several organelles that have specific functions It differs from the metabolism of animals, as they consume nutrients through their diet. Land plants have evolved complex body plans, which require developmental regulation of metabolism. They have evolved adaptive mechanisms that regulate metabolism to cope with terrestrial environments that are harsher than aquatic environments. We elucidate the regulatory functions of metabolites closely related to each other, focusing on four amino acids: O-acetylserine (OAS), S-adenosylmethionine (AdoMet), homocysteine (Hcy), and serine (Ser) (Table 1)

Objectives

Conclusion