The transketolase gene family of the resurrection plant Craterostigma plantagineum: differential expression during the rehydration phase.
Transketolases, key enzymes of the reductive and oxidative pentose phosphate pathways, are responsible for the synthesis of sugar phosphate intermediates. Here we report the first molecular analysis of transketolase genes from plants. Three distinct classes of transketolase-encoding cDNA clones were isolated from the desiccation-tolerant resurrection plant Craterostigma plantagineum. One class represented by the transcript tkt3 is constitutively expressed in leaves and roots under all physiological conditions tested. By biochemical analysis and protein sequencing of purified transketolase, it was shown that tkt3 is expressed in three enzymatically active isoforms. An intriguing discovery was that accumulation of the two other transketolase transcripts, tkt7 and tkt10, is preferentially associated with the rehydration process of the desiccated plant; whereas tkt10 is only expressed in leaves, tkt7 was detected in leaves and roots. This observation suggests a possible role for these transketolases in the conversion of sugars, which are a major phenomenon in the rehydration process. Despite an abundant level of tkt7 and tkt10 transcripts in rehydrating leaves, proteins could not be isolated. This is due in part to a translational control mechanism acting on the loading of mRNAs to polysomes.
Max-Planck-Institut für Züchtungsforschung, Köln, Germany.
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Bernacchia
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Schwall
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Lottspeich
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Salamini
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Bartels
D000220:Adaptation, Biological; D000595:Amino Acid Sequence; D001483:Base Sequence; D015152:Blotting, Northern; D015153:Blotting, Western; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics; D003890:Desiccation; D004926:Escherichia coli / Q000235:genetics; D018506:Gene Expression Regulation, Plant; D008969:Molecular Sequence Data; D005810:Multigene Family / Q000235:genetics*; D010940:Plant Proteins; D010944:Plants / Q000201:enzymology / Q000235:genetics*; D011132:Polyribosomes / Q000378:metabolism; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000032:analysis; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D014018:Tissue Distribution; D014174:Transketolase / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism; D014867:Water
D018076:DNA, Complementary; D010940:Plant Proteins; D012333:RNA, Messenger; D014867:Water; C092041:Tkt10 protein, Craterostigma plantagineum; C092040:Tkt3 protein, Craterostigma plantagineum; C092042:Tkt7 protein, Craterostigma plantagineum; D014174:Transketolase