The rice nuclear gene, VIRESCENT 2, is essential for chloroplast development and encodes a novel type of guanylate kinase targeted to plastids and mitochondria
In: The Plant Journal, Jg. 52 (2007-08-28), S. 512-527
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SummaryGuanylate kinase (GK) is a critical enzyme in guanine nucleotide metabolism pathways, catalyzing thephosphorylationof(d)GMPto(d)GDP.Hereweshowthatanovelgene,VIRESCENT2(V2),encodesanewtypeofGK(designatedpt/mtGK)thatislocalizedinplastidsandmitochondria.WeinitiallyidentifiedtheV2genebypositional cloning of the rice v2 mutant. The v2 mutant is temperature-sensitive and develops chlorotic leavesat restrictive temperatures. The v2 mutation causes inhibition of chloroplast differentiation; in particular, itdisruptsthe chloroplasttranslation machineryduring earlyleaf development[Sugimotoet al. (2004)PlantCellPhysiol. 45, 985]. In the bacterial and animal species studied to date, GK is localized in the cytoplasm andparticipatesinmaintenanceoftheguaninenucleotidepoolsrequiredformanyfundamentalcellularprocesses.PhenotypicanalysisofriceseedlingswithRNAiknockdownofcytosolicGK(designatedcGK)showedthatcGKisindispensableforthegrowthanddevelopmentofplants,butnotforchloroplastdevelopment.Thus,ricehastwotypesofGK, asdoesArabidopsis,suggestingthathigherplantshavetwotypesofGK. Ourresultssuggestthat, of the two types of GK, only pt/mtGK is essential for chloroplast differentiation.Keywords: rice,VIRESCENT2,plastidandmitochondrialguanylatekinase,chloroplastdevelopment,cytosolicguanylate kinase, Arabidopsis.IntroductionGuanine nucleotides are the major energy sources for manychemicalreactions,andarealsothebuildingblocksforDNA,RNA and some signaling molecules (e.g. cGMP). It has beenassumed that the biosynthetic processes for guaninenucleotides in higher plants are generally similar to those ofanimals and micro-organisms (Stasolla et al., 2003; Zrenneret al., 2006). GMP is synthesizedthroughtwo pathways: a denovo pathway that uses amino acids and other small mole-cules, and a salvage pathway that uses pre-formed guanineand guanosine. GMP can subsequently be phosphorylatedto GDP and GTP. However, the regulatory network for thesepathways in higher plants is much more complex than thatin animals. This increased complexity arises from the addi-tional presence of plastids in plant cells that can differentiateinto various types of organelle, such as chloroplasts, amy-loplasts and chromoplasts (Stasolla et al., 2003; Zrenneret al., 2006).Guanylate kinase (GK, ATP:GMP phosphotransferase; EC2.7.4.8) is an essential enzyme for the biosynthesis ofguanine nucleotides by catalysis of the reaction (d)GMP +ATP fi (d)GDP + ADP, where (d)GMP indicates GMP ordGMP. GK also plays an important role in the recycling ofthe second messenger cGMP (cGMP fi GMP fi GDP fiGTP fi cGMP), and is thought to regulate the supply ofguanine nucleotides to signal transduction pathway compo-nents (Gaidarov et al., 1993). In addition to these physiolo-gicalroles,thebiomedicalroleofhumanGKintheactivationof pro-drugs used for the treatment of cancers and viral
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The rice nuclear gene, VIRESCENT 2, is essential for chloroplast development and encodes a novel type of guanylate kinase targeted to plastids and mitochondria
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Autor/in / Beteiligte Person: | Iba, Koh ; Yoshimura, Atsushi ; Sugimoto, Hiroki ; Kusumi, Kensuke ; Yano, Masahiro ; Noguchi, Ko |
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Zeitschrift: | The Plant Journal, Jg. 52 (2007-08-28), S. 512-527 |
Veröffentlichung: | Wiley, 2007 |
Medientyp: | unknown |
ISSN: | 0960-7412 (print) |
DOI: | 10.1111/j.1365-313x.2007.03251.x |
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