75 Integrating Membrane Transport with Male Gametophyte ... - TAIR

325 Poplar Carbohydrate Active Enzymes. Gene Identification and Expression Analyses
Jane Geisler-Lee 1 , Matt Geisler 1 , Pedro Coutinho 2 , Bo Segerman 1 , Nobuyuki Nishikubo 1 , Junko Takahashi 1 , Henrik
Aspeborg 3 , Soraya Djerbi 3 , Emma Master 3 , Sara Andersson-Gunners 1 , Bjorn Sundberg 1 , Stanislaw Karpinski 4 , Tuula
T. Teeri Teeri 3 , Leszek Kleczkowski 1 , Bernard Henrissat 2 , Ewa Mellerowicz 1
1
Ume Plant Science Center, Umea, Sweden, 2 Architecture et Fonction des Macromolecules Biologiques,
Marseille, France, 3 Royal Institute of Technology, Stockholm, Sweden, 4 Stockholm University, Stockholm,
Sweden
Based on sequence homology, about 1,600 genes which encode carbohydrate active enzymes (CAZymes) in the
Populus trichocarpa genome were identified, annotated and assembled into families of glycosyltransferases (GTs), glycoside
hydrolases (GHs), carbohydrate esterase (CEs), polysaccharide lyases (PLs), and expansins (Exps). A collection of 100,000
expressed sequence tags from 17 different tissues was used to analyze CAZymes gene expression in poplar (Populus spp.)
and to compare to microarray data for poplar and Arabidopsis. Based on Fisher’s exact test (p≤5%), CAZyme families
and expansins were shown differentially expressed. The families with the highest levels of tissue-specific expression
generally are involved in cell wall carbohydrate biosynthesis and modification, or in starch biosynthesis and turnover.
Sucrose synthases and cellulose synthases were the most abundant transcripts specifically expressed in wood-forming
tissues. Woody tissues were the most plentiful source of different sucrose synthase and cellulose synthase transcripts
which demonstrates their importance in xylogenesis. Little expression of genes related to starch metabolism during wood
formation were found, which was consistent with the metabolic flux of carbon to cell wall biosynthesis. The CAZyme
transcriptomes in different poplar tissues showed profound changes; this led to some main differences in CAZyme genes
and their regulation between herbaceous and woody plants.
326 Functional Evidence for the Involvement of Arabidopsis IspF Homolog in the
Nonmevalonate Pathway of Plastid Isoprenoid Biosynthesis
Ming-Hsiun Hsieh 1 , Howard Goodman 2
1
Institute of Plant and Microbial Biology, Academia Sinica, Taipei, Taiwan , 2 Department of Molecular Biology,
Massachusetts General Hospital, Boston, MA 02114, USA
There are two independent pathways, the cytosolic mevalonate (MVA) pathway and the plastid nonmevalonate
(nonMVA) pathway, to synthesize isopentenyl diphosphate and dimethylallyl diphosphate in plants. Carotenoids and the
phytyl side chain of chlorophylls are isoprenoids derived from the plastid nonMVA pathway. All enzymes involved in the
nonMVA pathway have been identified in Escherichia coli. The E. coli IspF protein catalyzes a unique cyclization reaction
to convert 4-diphosphocytidyl-2-C-methyl-D-erythritol 2-phosphate into 2-C-methyl-D-erythritol 2,4-cyclodiphosphate
in the nonMVA pathway. We have characterized an Arabidopsis T-DNA insertion mutant, ispF-1, that has a null mutation
in the IspF gene. Homozygous ispF-1 mutants are albino lethal and the IspF transcripts are undetectable in these plants.
Moreover, the ispF-1 mutant chloroplasts are filled with vesicles instead of thylakoids. Amino acid sequence alignment
reveals that the IspF proteins are highly conserved between plants and bacteria. Interestingly, expression of the Arabidopsis
IspF protein can rescue the lethal phenotype of an E. coli ispF mutant. These results indicate that the Arabidopsis IspF
may share similar enzymatic mechanisms with the E. coli protein.