title: Chlorophyll-deficient mutants of Chlamydomonas reinhardtii that accumulate magnesium protoporphyrin IX.
abstract: Two Chlamydomonas reinhardtii mutants defective in CHLM encoding Mg-protoporphyrin IX methyltransferase (MgPMT) were identified. The mutants, one with a missense mutation (chlM-1) and a second mutant with a splicing defect (chlM-2), do not accumulate chlorophyll, are yellow in the dark and dim light, and their growth is inhibited at higher light intensities. They accumulate Mg-protoporphyrin IX (MgProto), the substrate of MgPMT and this may be the cause for their light sensitivity. In the dark, both mutants showed a drastic reduction in the amounts of core proteins of photosystems I and II and light-harvesting chlorophyll a/b-binding proteins. However, LHC mRNAs accumulated above wild-type levels. The accumulation of the transcripts of the LHC and other genes that were expressed at higher levels in the mutants during dark incubation was attenuated in the initial phase of light exposure. No regulatory effects of the constitutively 7- to 18-fold increased MgProto levels on gene expression were detected, supporting previous results in which MgProto and heme in Chlamydomonas were assigned roles as second messengers only in the transient activation of genes by light.
authors.affiliation: Fakultaet fuer Biologie, Institut fuer Biologie III, Universitaet Freiburg, Schaenzlestrasse 1, 79104, Freiburg, Germany.
authors.forename: Linda
authors.initials: L
authors.lastname: Meinecke
authors.forename: Ali
authors.initials: A
authors.lastname: Alawady
authors.forename: Michael
authors.initials: M
authors.lastname: Schroda
authors.forename: Robert
authors.initials: R
authors.lastname: Willows
authors.forename: Marilyn C
authors.initials: MC
authors.lastname: Kobayashi
authors.forename: Krishna K
authors.initials: KK
authors.lastname: Niyogi
authors.forename: Bernhard
authors.initials: B
authors.lastname: Grimm
authors.forename: Christoph F
authors.initials: CF
authors.lastname: Beck
mesh_terms: D020418:Algal Proteins / Q000737:chemistry / Q000235:genetics; D001483:Base Sequence; D002338:Carotenoids / Q000378:metabolism; D016825:Chlamydomonas reinhardtii / Q000235:genetics* / Q000378:metabolism / Q000528:radiation effects; D002734:Chlorophyll / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000528:radiation effects; D006418:Heme / Q000378:metabolism; D008027:Light; D045342:Light-Harvesting Protein Complexes / Q000378:metabolism; D008780:Methyltransferases / Q000737:chemistry / Q000235:genetics; D008969:Molecular Sequence Data; D009154:Mutation; D020125:Mutation, Missense; D011524:Protoporphyrins / Q000378:metabolism*; D012326:RNA Splicing; D012333:RNA, Messenger / Q000378:metabolism; D045725:Tetrapyrroles / Q000378:metabolism
chemical_list: D020418:Algal Proteins; D045342:Light-Harvesting Protein Complexes; D011524:Protoporphyrins; D012333:RNA, Messenger; D045725:Tetrapyrroles; D002734:Chlorophyll; C039629:magnesium protoporphyrin; D002338:Carotenoids; D006418:Heme; D008780:Methyltransferases; C060234:magnesium-protoporphyrin methyltransferase