title: Evolution of root-specific carotenoid precursor pathways for apocarotenoid signal biogenesis.
abstract: Various cleavage products of C40 carotenoid substrates are formed preferentially or exclusively in roots. Such apocarotenoid signaling or regulatory compounds differentially induced in roots during environmental stress responses including root colonization by arbuscular mycorrhizal fungi include ABA, strigolactones and C13 α-ionol/C14 mycorradicin derivatives. The low carotenoid levels in roots raise the question of whether there is a regulated precursor supply channeled into apocarotenoid formation distinct from default carotenoid pathways. This review describes root-specific isogene components of carotenoid pathways toward apocarotenoid formation, highlighting a new PSY3 class of phytoene synthase genes in dicots. It is clearly distinct from the monocot PSY3 class co-regulated with ABA formation. At least two members of the exclusive dicot PSY3s are regulated by nutrient stress and mycorrhization. This newly recognized dicot PSY3 (dPSY3 vs. mPSY3 from monocots) class probably represents an ancestral branch in the evolution of the plant phytoene synthase family. The evolutionary history of PSY genes is compared with the evolution of MEP pathway isogenes encoding 1-deoxy-d-xylulose 5-phosphate synthases (DXS), particularly DXS2, which is co-regulated with dPSY3s in mycorrhizal roots. Such stress-inducible isoforms for rate-limiting steps in root carotenogenesis might be components of multi-enzyme complexes committed to apocarotenoid rather than to carotenoid formation.
authors.affiliation: Leibniz-Institute of Plant Biochemistry, Department of Cell & Metabolic Biology, D-06120 Halle (Saale), Germany. Electronic address: mhwalter@ipb-halle.de.
authors.forename: Michael H
authors.initials: MH
authors.lastname: Walter
authors.affiliation: Leibniz-Institute of Plant Biochemistry, Department of Cell & Metabolic Biology, D-06120 Halle (Saale), Germany.
authors.forename: Ron
authors.initials: R
authors.lastname: Stauder
authors.affiliation: Leibniz-Institute of Plant Biochemistry, Department of Cell & Metabolic Biology, D-06120 Halle (Saale), Germany.
authors.forename: Alain
authors.initials: A
authors.lastname: Tissier
mesh_terms: D000220:Adaptation, Biological; D005075:Biological Evolution; D002338:Carotenoids / Q000378:metabolism*; D018521:Plant Physiological Phenomena; D018517:Plant Roots / Q000378:metabolism*; D013312:Stress, Physiological
chemical_list: D002338:Carotenoids
keywords: 1-Deoxy-d-xylulose 5-phosphate synthase (DXS); Apocarotenoids; Arbuscular mycorrhiza; Mycorradicin; Phytoene synthase (PSY); Strigolactones