Expression of desiccation-related proteins from the resurrection plant Craterostigma plantagineum in transgenic tobacco

Three cDNAs encoding desiccation-induced proteins from the resurrection plant Craterostigma plantagineum were each ligated to a triplicated CaMV 35S promoter and a nopaline synthase 3-flanking region in an Agrobacterium vector and introduced into tobacco. Transgenic plants expressed the encoded Craterostigma proteins at high levels. This did not lead to changes in the phenotype, in the growth habit or in basic photosynthetic parameters. In tobacco, one protein was targeted to the chloroplast stroma which is its normal location in Craterostigma. These desiccation-related proteins are not sufficient per se to increase drought tolerance as measured by ion-leakage tests.     

Constitutive expression of small heat shock proteins in vegetative tissues of the resurrection plant Craterostigma plantagineum

Using antibodies raised against two sunflower small heat shock proteins (sHSPs), we have detected immunologically related proteins in unstressed vegetative tissues from the resurrection plant Craterostigma plantagineum. In whole plants, further accumulation of these polypeptides was induced by heat-shock or water-stress. In desiccation-intolerant Craterostigma callus tissue, we failed to detect sHSP-related polypeptides, but their expression, and the concurrent acquisition of desiccation tolerance was induced by exogenous abscisic acid (ABA) treatment. In untressed plants, the cross-reacting polypeptides were abundant in the roots and lower part of the shoots, where they showed homogeneous tissue-distributions. This constitutive expression is novel for vegetative tissues of higher plants, and resembles the expression patterns of sHSPs in desiccation-tolerant zygotic embryos and germinating seeds.J.A. and C.A. contributed equally to this work and are both considered to be first author     

Retrotransposons and siRNA have a role in the evolution of desiccation tolerance leading to resurrection of the plant Craterostigma plantagineum

* Craterostigma plantagineum can lose up to 96% of its water content but fully recover within hours after rehydration. The callus tissue of the plant becomes desiccation tolerant upon pre-incubation with abscisic acid (ABA). In callus and vegetative organs, ABA addition and water depletion induce a set of dehydration-responsive genes. * Previously, activation tagging led to the isolation of Craterostigma desiccation tolerant (CDT-1), a dehydration-related ABA-inducible gene which renders callus desiccation tolerant without ABA pre-treatment. This gene belongs to a family of retroelements, members of which are inducible by dehydration. * Craterostigma plantagineum transformation with mutated versions of CDT-1 indicated that protein is not required for the induction of callus desiccation tolerance. Northern analysis and protoplast transfection indicated that CDT-1 directs the synthesis of a double-stranded 21-bp short interfering RNA (siRNA), which opens the metabolic pathway for desiccation tolerance. * Via transposition, these retroelements have progressively increased the capacity of the species to synthesize siRNA and thus recover after dehydration. This may be a case of evolution towards the acquisition of a new trait, stimulated by the environment acting directly on intra-genomic DNA replication.     

Photosynthetic carbohydrate metabolism in the resurrection plant Craterostigma plantagineum

The resurrection plant Craterostigma plantagineum (Hochst) is able to survive almost complete tissue dehydration when water is withheld from it, and then can rehydrate rapidly on rewatering. This ability is believed to be the result of the accumulation of sucrose in aerial tissues as a result of metabolism of 2-octulose. In this work the metabolic activity of well-watered Craterostigma plantagineum plants has been investigated. It is shown that Craterostigma makes raffinose series oligosaccharides as a product of photosynthesis and translocates them in the phloem. Evidence is also provided that 2-octulose is a product of photosynthesis and accumulates in the leaves over the light period and is mobilized at night. Thus 2-octulose acts as a temporary storage carbohydrate in leaves during photosynthesis in a similar fashion to starch in most C3 plants. Other potential roles of 2-octulose are discussed. Other than these observations Craterostigma plants are very similar to other C3 plants under these conditions.