title: Lysine catabolism, an effective versatile regulator of lysine level in plants.
abstract: Lysine is a nutritionally important essential amino acid, whose synthesis in plants is strongly regulated by the rate of its synthesis. Yet, lysine level in plants is also finely controlled by a super-regulated catabolic pathway that catabolizes lysine into glutamate and acetyl Co-A. The first two enzymes of lysine catabolism are synthesized from a single LKR/SDH gene. Expression of this gene is subject to compound developmental, hormonal and stress-associated regulation. Moreover, the LKR/SDH gene of different plant species encodes up to three distinct polypeptides: (i) a bifunctional enzyme containing the linked lysine-ketoglutarate (LKR) and saccharopine dehydrogenase (SDH) whose LKR activity is regulated by its linked SDH enzyme; (ii) a monofunctional SDH encoded by an internal promoter, which is a part of the coding DNA region of the LKR/SDH gene; and (iii) a monofunctional, highly potent LKR that is formed by polyadenylation within an intron. LKR activity in the bifunctional LKR/SDH polypeptide is also post-translationally regulated by phosphorylation by casein kinase-2 (CK2), but the consequence of this regulation is still unknown. Why is lysine metabolism super-regulated by synthesis and catabolism? A hypothesis addressing this important question is presented, suggesting that lysine may serve as a regulator of plant growth and interaction with the environment.
authors.affiliation: Department of Plant Sciences, The Weizmann Institute of Science, Rehovot, Israel.
authors.forename: A
authors.initials: A
authors.lastname: Stepansky
authors.forename: H
authors.initials: H
authors.lastname: Less
authors.forename: R
authors.initials: R
authors.lastname: Angelovici
authors.forename: R
authors.initials: R
authors.lastname: Aharon
authors.forename: X
authors.initials: X
authors.lastname: Zhu
authors.forename: G
authors.initials: G
authors.lastname: Galili
mesh_terms: D000818:Animals; D018506:Gene Expression Regulation, Plant; D006706:Homeostasis; D008239:Lysine / Q000378:metabolism*; D010940:Plant Proteins / Q000378:metabolism; D010944:Plants / Q000378:metabolism*
chemical_list: D010940:Plant Proteins; D008239:Lysine