Amino Acids in Rice Grains and Their Regulation by Polyamines and Phytohormones

Abstract

Rice is one of the most important food crops in the world, and amino acids in rice grains are major nutrition sources for the people in countries where rice is the staple food. Phytohormones and plant growth regulators play vital roles in regulating the biosynthesis of amino acids in plants. This paper reviewed the content and compositions of amino acids and their distribution in different parts of ripe rice grains, and the biosynthesis and metabolism of amino acids and their regulation by polyamines (PAs) and phytohormones in filling grains, with a focus on the roles of higher PAs (spermidine and spermine), ethylene, and brassinosteroids (BRs) in this regulation. Recent studies have shown that higher PAs and BRs (24-epibrassinolide and 28-homobrassinolide) play positive roles in mediating the biosynthesis of amino acids in rice grains, mainly by enhancing the activities of the enzymes involved in amino acid biosynthesis and sucrose-to-starch conversion and maintaining redox homeostasis. In contrast, ethylene may impede amino acid biosynthesis by inhibiting the activities of the enzymes involved in amino acid biosynthesis and elevating reactive oxygen species. Further research is needed to unravel the temporal and spatial distribution characteristics of the content and compositions of amino acids in the filling grain and their relationship with the content and compositions of amino acids in different parts of a ripe grain, to elucidate the cross-talk between or among phytohormones in mediating the anabolism of amino acids, and to establish the regulation techniques for promoting the biosynthesis of amino acids in rice grains.

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Genome-wide association studies of five free amino acid levels in rice

“…In addition to the basic unit in protein biosynthesis, amino acids are involved in several cellular responses to affect physiological processes in plants, such as plant growth and development, intracellular pH control, production of metabolic energy or redox capacity, signal transduction, and response to abiotic and biotic stresses ( Moe, 2013 ; Watanabe et al., 2013 ; Zeier, 2013 ; Fagard et al., 2014 ; Galili et al., 2014 ; Pratelli and Pilot, 2014 : Hausler et al., 2014 ; Hildebrandt et al., 2015 ). Free amino acids (FAAs) not only play essential roles in plant growth, development, and responses to stress, but also serve as important nutrients for human health ( Pathria and Ronai, 2021 ; Yang et al., 2022 ). Of all the amino acids, tryptophan (Trp), isoleucine (Ile), leucine (Leu), and valine (Val) are essential amino acids that are based on plants and cannot synthesize from external sources ( Galili et al., 2016 ).…”