Arginine, a key amino acid for nitrogen nutrition and metabolism of forest trees.

Despite the extraordinary significance of forests from an environmental, economic, and social perspectives, our understanding of the mechanisms underlying the growth, development and productivity of forest trees remains limited compared to crop plants, mainly due to their perennial growth and difficulty of molecular analysis. Amino acids and peptides are key nitrogen (N) sources available in the soil for tree nutrition. Furthermore, when excess N is available, trees can assimilate and store it directly as free arginine, the amino acid with the highest N content, or as a constituent of storage proteins in vegetative and reproductive organs. Arginine is, therefore, of paramount importance in N metabolism, and studying its biosynthesis and metabolic utilization is crucial for understanding N homeostasis in forest trees. This work reviews several aspects of arginine biochemistry and molecular biology in woody plants, including its transport, storage, and mobilization, as well as the enzymes involved in its biosynthesis and their subcellular distribution. Arginine biosynthesis is allosterically controlled by pathway's end-product, and increased glutamine levels act as a signal of N abundance, triggering a response that enhances flux through the pathway, favoring N storage. Additionally, this review discusses the molecular regulation of arginine biosynthesis at both transcriptional and post-transcriptional levels, with an emphasis on key processes such as embryogenesis and N recycling.