Subcellular localization and enzymatic properties of differentially expressed transketolase genes isolated from the desiccation tolerant resurrection plant Craterostigma plantagineum

Abstract

The desiccation tolerant resurrection plant Craterostigma plantagineum encodes three classes of transketolase transcripts, which are distinguished by their gene structures and their expression patterns. One class, represented by tkt3, is constitutively expressed and two classes, represented by tkt7 and tkt10, are upregulated upon rehydration of desiccated C. plantagineum plants. The objective of this work was to characterize the differentially expressed transketolase isoforms with respect to subcellular localization and enzymatic activity. Using GFP fusion constructs and enzymatic activity assays, we demonstrate that C. plantagineum has novel forms of transketolase which localize not to the chloroplast, but mainly to the cytoplasm and which are distinct in the enzymatic properties from the transketolase enzymes active in the Calvin cycle or oxidative pentose phosphate pathway. A transketolase preparation from rehydrated leaves was able to synthesize the unusual C8 carbon sugar octulose when glucose-6-phosphate and hydroxy-pyruvate were used as acceptor and donor molecules in in vitro assays. This suggests that a transketolase catalyzed reaction is likely to be involved in the octulose biosynthesis in C. plantagineum.

Effects of overexpressing photosynthetic carbon flux control enzymes in the cyanobacterium Synechocystis PCC 6803

“…Its function requires thiamine pyrophosphate as a cosubstrate (Willige et al, 2009). Substrates and products of TK are precursors for the synthesis of nucleic acids, aromatic amino acids and vitamins (Kochetov, 2001).…”

Enzymes and Metabolites in Carbohydrate Metabolism of Desiccation Tolerant Plants

“…Thus, only further identification of the cellular localization and properties of enzymes with multiple roles can help to understand the contribution of these enzymes to desiccation tolerance. The studies on transketolase of C. plantagineum from Bernacchia et al (1995), Willige et al (2009), and Zhang et al (2016) provide an example for this proposal: three isoforms of transketolase (tkt3, tkt7, and tkt10) have been characterized on the molecular level in C. plantagineum ; tkt3 is localized in chloroplasts while tkt7 and tkt10 are localized in the cytoplasm; tkt3 is suggested to be involved in carbon reactions in photosynthesis and the pentose phosphate pathway, while tkt7 and tkt10 are involved in the accumulation of octulose in C. plantagineum [67,68,69]. …”

“…To prevent damage associated with oxidative stress, resurrection plants have evolved various protective mechanisms [82]. Many resurrection plants, such as L. brevidens [69] or M. flabellifolia [68] will accumulate anthocyanins that have a basic structure composed of carbon and act as photoprotective light screens in vegetative tissues [83]. To respond to ROS produced by dehydration stress, plants induce antioxidant defense systems.…”

Low and high ψ ways from post-transcriptional RNA regulation to drought tolerance

“…The role of sugars, enzymes of carbohydrate metabolism as well as expression and regulation of proteins with cellular protective functions have been described in great detail in this system. 24,25 Plants on the other extreme may operate a different way. They do not tolerate desiccation but try to keep high water potential as long as possible for survival.…”