A phylogenetic study of cytochrome b561 proteins. (1/8)

BACKGROUND: As an antioxidant and cofactor to numerous metabolic enzymes, ascorbate has an essential role in plants and animals. Cytochromes b561 constitute a class of intrinsic membrane proteins involved in ascorbate regeneration. Despite their importance in ascorbate metabolism, no evolutionary analysis has been presented so far on this newly described protein family. RESULTS: Cytochromes b561 have been identified in a large number of phylogenetically distant species, but are absent in fungi and prokaryotes. Most species contain three or four cytochrome b561 paralogous proteins, and the encoding genes usually have four or five exons. At the protein level, sequence similarities are rather low between cytochromes b561 within a single species (34-45% identity), and among phylogenetically distant species (around 30% identity). However, particular structural features characterizing this protein family are well conserved in members from all species investigated. These features comprise six transmembrane helices, four strictly conserved histidine residues, probably coordinating the two heme molecules, and putative ascorbate and monodehydro-ascorbate (MDHA) substrate-binding sites. Analysis of plant cytochromes b561 shows a separation between those from monocotyledonous and dicotyledonous species in a phylogenetic tree. CONCLUSIONS: All cytochromes b561 have probably evolved from a common ancestral protein before the separation of plants and animals. Their phyletic distribution mirrors the use of ascorbate as primary antioxidant, indicating their role in ascorbate homeostasis and antioxidative defense. In plants, the differentiation into four cytochrome b561 isoforms probably occurred before the separation between monocots and dicots.  (+info)

Investigation into the ability of roots of the poikilohydric plant Craterostigma plantagineum to survive dehydration stress. (2/8)

The ability of the root system of the poikilohydric plant Craterostigma plantagineum to survive dehydration was investigated. The data presented here reveal that the root system is capable of surviving dehydration, but shortly after rehydration the root system senesces. Two weeks after rehydration the growth of a complete new root system is initiated. During dehydration sucrose accumulates from 36 to a maximum of 111 micromol g-1 DW in the roots. It is suggested that the accumulation of sucrose protects the root system during dehydration. There are major stores of stachyose in the roots of Craterostigma (making up over 40% of the dry weight of the tissue) and during dehydration these stores are metabolized. It is suggested that these stachyose stores act as carbohydrate reserves for the synthesis of sucrose. However, over 350 micromol g-1 DW stachyose is metabolized in the roots, which is well in excess of that required for the accumulation of sucrose observed. It is likely that the stachyose reserves in the root system are translocated to other regions of the plant to support carbohydrate metabolism during dehydration of the tissue. During rehydration, the stachyose reserves return to their original level within 96 h. There is no change in the elevated sucrose content of the roots over this period. Thus the roots maintain the protective properties of sucrose much longer than they are needed. The maintenance of high sucrose contents in rehydrating roots is discussed as a possible survival strategy against recurrent desiccation events.  (+info)

Photosynthetic genes are differentially transcribed during the dehydration-rehydration cycle in the resurrection plant, Xerophyta humilis. (3/8)

One of the desiccation-tolerant mechanisms of the resurrection plant, Xerophyta humilis, is the ability to shut down photosynthesis reversibly. The X. humilis psbR and ChlP genes, encoding the 10 kDa polypeptide of photosystem II (PSII) and a geranylgeranyl reductase, respectively, were isolated in a differential display screen as dehydration-down-regulated and rehydration-up-regulated transcripts. Two other PSII genes, psbA (chloroplast-encoded) and psbP (nuclear-encoded), isolated by degenerate primer PCR, display a similar trend in expression.  (+info)

A role for expansins in dehydration and rehydration of the resurrection plant Craterostigma plantagineum. (4/8)

Craterostigma plantagineum is one of the few higher plants capable of surviving desiccation throughout its vegetative tissues. Water loss results in cell shrinkage and a commensurate folding of the cell wall indicating an unusual degree of wall flexibility. We show that wall extensibility undergoes a marked increase during dehydration and rehydration. Similar increases were observed in the activity of expansins in cell walls during these processes suggesting a role for these proteins in increasing wall flexibility. Three alpha-expansin cDNAs were cloned from dehydrating leaves and transcript levels for one correlated closely with the observed changes in expansin activity during the dehydration and rehydration of leaves.  (+info)

Stress tolerance and glucose insensitive phenotypes in Arabidopsis overexpressing the CpMYB10 transcription factor gene. (5/8)

The resurrection plant Craterostigma plantagineum has the ability to survive complete dehydration. In an attempt to further understand desiccation tolerance in this plant, the CpMYB10 transcription factor gene was functionally characterized. CpMYB10 is rapidly induced by dehydration and abscisic acid (ABA) treatments in leaves and roots, but no expression was detected in fully hydrated tissues. Electrophoretic mobility shift assay experiments showed binding of rCpMYB10 to specific mybRE elements within the LEA Cp11-24 and CpMYB10 promoters. Localization of CpMYB10 transcript by in situ reverse transcription-PCR reactions showed expression in vascular tissues, parenchyma, and epidermis both in leaves and roots in response to ABA. Transgenic Arabidopsis plants transformed with CpMYB10 promoter fused to GUS gene showed reporter expression under ABA and stress conditions in several organs. Overexpression of CpMYB10 cDNA in Arabidopsis led to desiccation and salt tolerance of transgenics lines. Interestingly, it was found that plants overexpressing CpMYB10 exhibited Glc-insensitive and ABA hypersensitive phenotypes. Therefore, our results indicate that CpMYB10 in Arabidopsis is mediating stress tolerance and altering ABA and Glc signaling responses.  (+info)

Simultaneous in vivo recording of prompt and delayed fluorescence and 820-nm reflection changes during drying and after rehydration of the resurrection plant Haberlea rhodopensis. (6/8)

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Polyamine metabolic canalization in response to drought stress in Arabidopsis and the resurrection plant Craterostigma plantagineum. (7/8)

In this work, we have studied the transcriptional profiles of polyamine biosynthetic genes and analyzed polyamine metabolic fluxes during a gradual drought acclimation response in Arabidopsis thaliana and the resurrection plant Craterostigma plantagineum. The analysis of free putrescine, spermidine and spermine titers in Arabidopsis arginine decarboxylase (adc1-3, adc2-3), spermidine synthase (spds1-2, spds2-3) and spermine synthase (spms-2) mutants during drought stress, combined with the quantitative expression of the entire polyamine biosynthetic pathway in the wild-type, has revealed a strong metabolic canalization of putrescine to spermine induced by drought. Such canalization requires spermidine synthase 1 (SPDS1) and spermine synthase (SPMS) activities and, intriguingly, does not lead to spermine accumulation but to a progressive reduction in spermidine and spermine pools in the wild-type. Our results suggest the participation of the polyamine back-conversion pathway during the drought stress response rather than the terminal catabolism of spermine. The putrescine to spermine canalization coupled to the spermine to putrescine back-conversion confers an effective polyamine recycling-loop during drought acclimation. Putrescine to spermine canalization has also been revealed in the desiccation tolerant plant C. plantagineum, which conversely to Arabidopsis, accumulates high spermine levels which associate with drought tolerance. Our results provide a new insight to the polyamine homeostasis mechanisms during drought stress acclimation in Arabidopsis and resurrection plants.  (+info)

The lysine-rich motif of intrinsically disordered stress protein CDeT11-24 from Craterostigma plantagineum is responsible for phosphatidic acid binding and protection of enzymes from damaging effects caused by desiccation. (8/8)

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