Overexpression of the Selaginella lepidophylla bHLH transcription factor enhances water-use efficiency, growth, and development in Arabidopsis

Abiotic stresses have the greatest impact on the growth and productivity of crops, especially under current and future extreme weather events due to climate change. Thus, it is vital to explore novel strategies to improve crop plant abiotic stress tolerance to feed an ever-growing world population. Selaginella lepidophylla is a desiccation-tolerant spike moss with specialized adaptations that allow it to tolerate water loss down to 4% relative water content. A candidate basic helix-loop-helix (bHLH) transcription factor was highly expressed at 4% relative water content in S. lepidophylla (SlbHLH). This SlbHLH gene was codon-optimized (SlbHLH_opt) and overexpressed in Arabidopsis for functional characterization. Overexpression of the SlbHLH_opt gene not only significantly increased plant growth, development, and integrated water-use efficiency, but also significantly increased seed germination and green cotyledon emergence rates under water-deficit stress and salt stress conditions. Under a 150 mM NaCl salt stress condition, SlbHLH_opt-overexpressing lines increased primary root length, the number of lateral roots, and fresh and dry biomass at the seedling stage compared to control lines. Interestingly, SlbHLH_opt-overexpressing lines also have significantly higher flavonoid content. Altogether, these results suggest that SlbHLH functions as an important regulator of plant growth, development, abiotic stress tolerance, and water-use efficiency.

GingerRoot: A Novel DNA Transposon Encoding Integrase-Related Transposase in Plants and Animals

Transposable elements represent the largest components of many eukaryotic genomes and different genomes harbor different combinations of elements. Here, we discovered a novel DNA transposon in the genome of the clubmoss Selaginella lepidophylla. Further searching for related sequences to the conserved DDE region uncovered the presence of this superfamily of elements in fish, coral, sea anemone, and other animal species. However, this element appears restricted to Bryophytes and Lycophytes in plants. This transposon, named GingerRoot, is associated with a 6 bp (base pair) target site duplication, and 100-150 bp terminal inverted repeats. Analysis of transposase sequences identified the DDE motif, a catalytic domain, which shows similarity to the integrase of Gypsy-like long terminal repeat retrotransposons, the most abundant component in plant genomes. A total of 77 intact and several hundred truncated copies of GingerRoot elements were identified in S. lepidophylla. Like Gypsy retrotransposons, GingerRoots show a lack of insertion preference near genes, which contrasts to the compact genome size of about 100 Mb. Nevertheless, a considerable portion of GingerRoot elements was found to carry gene fragments, suggesting the capacity of duplicating gene sequences is unlikely attributed to the proximity to genes. Elements carrying gene fragments appear to be less methylated, more diverged, and more distal to genes than those without gene fragments, indicating they are preferentially retained in gene-poor regions. This study has identified a broadly dispersed, novel DNA transposon, and the first plant DNA transposon with an integrase-related transposase, suggesting the possibility of de novo formation of Gypsy-like elements in plants.

A Polyamine Oxidase from Selaginella lepidophylla (SelPAO5) can Replace AtPAO5 in Arabidopsis through Converting Thermospermine to Norspermidine instead to Spermidine

Of the five polyamine oxidases in Arabidopsis thaliana, AtPAO5 has a substrate preference for the tetraamine thermospermine (T-Spm) which is converted to triamine spermidine (Spd) in a back-conversion reaction in vitro. A homologue of AtPAO5 from the lycophyte Selaginella lepidophylla (SelPAO5) back-converts T-Spm to the uncommon polyamine norspermidine (NorSpd) instead of Spd. An Atpao5 loss-of-function mutant shows a strong reduced growth phenotype when growing on a T-Spm containing medium. When SelPAO5 was expressed in the Atpao5 mutant, T-Spm level decreased to almost normal values of wild type plants, and NorSpd was produced. Furthermore the reduced growth phenotype was cured by the expression of SelPAO5. Thus, a NorSpd synthesis pathway by PAO reaction and T-Spm as substrate was demonstrated in planta and the assumption that a balanced T-Spm homeostasis is needed for normal growth was strengthened.

Exploratory studies of some Mexican medicinal plants: Cardiovascular effects in rats with and without hypertension

Background:

Papaveraceae Argemone mexicana L., Burseraceae Bursera simaruba (L.) Sarg., Acanthaceae Justicia spicigera Schltdl. and Selaginellaceae Selaginella lepidophylla (Hook. & Grev.) Spring., have been used in Mexican traditional medicine to treat hypertension. The objective of this study was to further characterize the cardiovascular effects of the methanol extracts of such plants.

Methods:

The medicinal plants were collected and taxonomically identified; the methanol extract of each explored plant were administrated to conscious and unconscious male Wistar rats with and without glucose-induced hypertension. The blood pressure (BP) and heart rate (HR) were evaluated before and after the extract administration. Vascular reactivity experiments were conducted in rat aortic rings obtained from rats with and without sugar-induced hypertension, a model widely used to study such effects with cardiovascular agents.

Results:

After oral administration in normotensive conscious rats all tested extracts decreased the HR, such effect was only observed in hypertensive conscious rats after the administration of B. simaruba; only A. mexicana and B. simaruba decreased the BP after oral administration. All extracts administrated by intravenous injection diminished the mean arterial pressure. Dose-response curves to cumulative concentrations of all the extracts promote vascular relaxation in precontracted aortas from rats with and without sugar-induced hypertension.

Conclusions:

The present study indicated that B. simaruba is worthy of further investigation as a potential phytotherapeutic agent for treating hypertension.

The polyamine oxidase from lycophyte Selaginella lepidophylla (SelPAO5), unlike that of angiosperms, back-converts thermospermine to norspermidine

In the phylogeny of plant polyamine oxidases (PAOs), clade III members from angiosperms, such as Arabidopsis thaliana PAO5 and Oryza sativa PAO1, prefer spermine and thermospermine as substrates and back-convert both of these substrates to spermidine in vitro. A clade III representative of lycophytes, SelPAO5 from Selaginella lepidophylla, also prefers spermine and thermospermine but instead back-converts these substrates to spermidine and norspermidine, respectively. This finding indicates that the clade III PAOs of lycophytes and angiosperms oxidize thermospermine at different carbon positions. We discuss the physiological significance of this difference.

The polyamine oxidase from lycophyte Selaginella lepidophylla (SelPAO5), unlike that of angiosperms, back-converts thermospermine to norspermidine

In the phylogeny of plant polyamine oxidases (PAOs), clade III members from angiosperms, such as Arabidopsis thaliana PAO5 and Oryza sativa PAO1, prefer spermine and thermospermine as substrates and back-convert both of these substrates to spermidine in vitro. A clade III representative of lycophytes, SelPAO5 from Selaginella lepidophylla, also prefers spermine and thermospermine but instead back-converts these substrates to spermidine and norspermidine, respectively. This finding indicates that the clade III PAOs of lycophytes and angiosperms oxidize thermospermine at different carbon positions. We discuss the physiological significance of this difference.

Evaluation of the diuretic activity in two Mexican medicinal species: Selaginella nothohybrida and Selaginella lepidophylla and its effects with ciclooxigenases inhibitors

ETHNOPHARMACOLOGICAL RELEVANCE

Doradilla is a plant that has a long history in the Mexican traditional system of medicine for gall and renal stones, diuresis, stomach and liver inflammation among other diseases. Major components isolated from these plants include biflavonoids as amentoflavone (1), robustaflavone (2) and (S)-2,3-dihydrorobustaflavone (3) and the carbohydrate trehalose (4). The aim of this study was to evaluate the diuretic effect of the decoction of Selaginella nothohybrida Valdespino and Selaginella lepidophylla (Hook & Grev) Spring (Selaginellaceae), and compounds 1-4. We also explored the probable mode of action comparing the effects when using nonspecific and specific COX׳s inhibitors.

MATERIALS AND METHODS

Three biflavonoids (1-3) were isolated from the ethyl acetate extraction of the aqueous decoction and the carbohydrate trehalose (4) from the aqueous phase. The structures of all compounds were elucidated by spectroscopic methods and comparisons were made against published data. The diuretic activity was assessed in mice by oral administration of the decoctions in doses of 1000 and 2000mg/kg and biflavonoids 1-3 and trehalose (4) in a dose range of 10mg/kg using furosemide as a standard drug. Inhibitors of COX׳s such as acetyl salicylic acid, sodium naproxen, indomethacin and Celebrex were also assayed to analyze the involvement of renal prostaglandins in diuresis. Water excretion rate, pH, density, conductivity, and contents of Na(+) and K(+) were measured in the urine of mice.

RESULTS

Decoction of Selaginella lepidophylla showed lower effect in the urine output at doses of 1000 and 2000mg/kg, while decoction of Selaginella nothohybrida produced an increase at 2000mg/kg (P<0.05). Urinary electrolytes excretion was also affected by this last extract and pure compounds: decoction diminished urinary excretion of sodium and potassium ions, so as compounds 1 and 4; compounds 2 and 3 observed just a natriuretic effect. Pretreated mice with COX׳s inhibitors and then with test compounds 1, 2, 4 and decoction showed inhibition of diuresis in all cases exception for treatment with trehalose (4); natriuretic effect was observed in all cases except for biflavonoid robustaflavone (2) which behaved as the reference compound furosemide. Selaginella nothohybrida decoction behaved similarly to COX-2 inhibitor Celebrex (8), inhibiting diuresis.

CONCLUSIONS

Selaginella nothohybrida presents a moderate diuretic effect, which appears to be in partly mediated by the presence of biflavonoids and trehalose. Renal prostaglandins may be involved in the mechanism of diuresis. The present results provide a quantitative basis explaining the traditional folk medicine use of Selaginella nothohybrida as a diuretic agent by Mexican population.

The desiccation tolerant secrets of Selaginella lepidophylla: what we have learned so far?

Selaginella lepidophylla is a desiccation tolerant plant able to survive complete vegetative tissue dehydration and revive ('resurrect') in water conditions. Vegetative desiccation tolerance is an adaptive feature acquired by S. lepidophylla to withstand the long dry periods in its natural habitat, the Chihuahuan desert. Understanding the molecular basis of its drought stress tolerance may be of great benefit to help in developing novel strategies for improvement of drought stress tolerance in crops. Cell biological (e.g. gene discovery, comparative EST analysis, proteomics, metabolite profiling), ultrastructural and physiological studies have brought modest but already important insights in the desiccation tolerance mechanisms adapted by S. lepidophylla. Until recently, the desiccation tolerant mechanism of S. lepidophylla was related to its high trehalose levels. However, large-scale comparative metabolic analysis between S. lepidophylla and its desiccation susceptible relative Selaginella moellendorffii, unexpectedly revealed that S. moellendorffii contains higher trehalose levels than S. lepidophylla. Interestingly, polyols, such as sorbitol and xylitol are 100× more abundant in S. lepidophylla compared to S. moellendorffii. Whether this is linked to the higher stress tolerance remains to be established. Apart from these metabolites, we will also discuss the ultrastructural features that seem to play an important role in the desiccation tolerance of S. lepidophylla. Finally we discuss desiccation tolerance mechanism in other plant species.

Comparative metabolic profiling between desiccation-sensitive and desiccation-tolerant species of Selaginella reveals insights into the resurrection trait

Spike mosses (Selaginellaceae) represent an ancient lineage of vascular plants in which some species have evolved desiccation tolerance (DT). A sister-group contrast to reveal the metabolic basis of DT was conducted between a desiccation-tolerant species, Selaginella lepidophylla, and a desiccation-sensitive species, Selaginella moellendorffii, at 100% relative water content (RWC) and 50% RWC using non-biased, global metabolomics profiling technology, based on GC/MS and UHLC/MS/MS(2) platforms. A total of 301 metabolites, including 170 named (56.5%) and 131 (43.5%) unnamed compounds, were characterized across both species. S.  lepidophylla retained significantly higher abundances of sucrose, mono- and polysaccharides, and sugar alcohols than did S. moellendorffii. Aromatic amino acids, the well-known osmoprotectant betaine and flavonoids were also more abundant in S. lepidophylla. Notably, levels of γ-glutamyl amino acid, linked with glutathione metabolism in the detoxification of reactive oxygen species, and with possible nitrogen remobilization following rehydration, were markedly higher in S. lepidophylla. Markers for lipoxygenase activity were also greater in S. lepidophylla, especially at 50% RWC. S. moellendorffii contained more than twice the number of unnamed compounds, with only a slightly greater abundance than in S. lepidophylla. In contrast, S. lepidophylla contained 14 unnamed compounds of fivefold or greater abundance than in S. moellendorffii, suggesting that these compounds might play critical roles in DT. Overall, S. lepidophylla appears poised to tolerate desiccation in a constitutive manner using a wide range of metabolites with some inducible components, whereas S. moellendorffii mounts only limited metabolic responses to dehydration stress.

Comparative metabolic profiling between desiccation-sensitive and desiccation-tolerant species of Selaginella reveals insights into the resurrection trait

Spike mosses (Selaginellaceae) represent an ancient lineage of vascular plants in which some species have evolved desiccation tolerance (DT). A sister-group contrast to reveal the metabolic basis of DT was conducted between a desiccation-tolerant species, Selaginella lepidophylla, and a desiccation-sensitive species, Selaginella moellendorffii, at 100% relative water content (RWC) and 50% RWC using non-biased, global metabolomics profiling technology, based on GC/MS and UHLC/MS/MS(2) platforms. A total of 301 metabolites, including 170 named (56.5%) and 131 (43.5%) unnamed compounds, were characterized across both species. S.  lepidophylla retained significantly higher abundances of sucrose, mono- and polysaccharides, and sugar alcohols than did S. moellendorffii. Aromatic amino acids, the well-known osmoprotectant betaine and flavonoids were also more abundant in S. lepidophylla. Notably, levels of γ-glutamyl amino acid, linked with glutathione metabolism in the detoxification of reactive oxygen species, and with possible nitrogen remobilization following rehydration, were markedly higher in S. lepidophylla. Markers for lipoxygenase activity were also greater in S. lepidophylla, especially at 50% RWC. S. moellendorffii contained more than twice the number of unnamed compounds, with only a slightly greater abundance than in S. lepidophylla. In contrast, S. lepidophylla contained 14 unnamed compounds of fivefold or greater abundance than in S. moellendorffii, suggesting that these compounds might play critical roles in DT. Overall, S. lepidophylla appears poised to tolerate desiccation in a constitutive manner using a wide range of metabolites with some inducible components, whereas S. moellendorffii mounts only limited metabolic responses to dehydration stress.

Changes of fluorescence and xanthophyll pigments during dehydration in the resurrection plantSelaginella lepidophylla in low and medium light intensities

The changes in photosynthetic efficiency and photosynthetic pigments during dehydration of the resurrection plantSelaginella lepidophylla (from the Chiuhahuan desert, S.W. Texas, USA) were examined under different light conditions. Changes in the photosynthetic efficiency were deduced from chlorophyll a fluorescence measurements (F_o, F_m, and F_v) and pigment changes were measured by HPLC analysis. A small decrease in F_v/F_m was seen in hydrated stems in high light (650 μmol photons·m^-2·s^-1) but not in low light (50 μmol photons·m^-2·s^-1). However, a pronounced decline in F_v/F_m was observed during dehydration in both light treatments, after one to two hours of dehydration. A rise in F_o was observed only after six to ten hours of dehydration. Concomitant with the decrease in photosynthetic efficiency during dehydration a rise in the xanthophyll zeaxanthin was observed, even in low-light treatments. The increase in zeaxanthin can be related to previously observed photoprotective non-photochemical quenching of fluorescence in dehydrating stems ofS. lepidophylla. We hypothesize that under dehydrating conditions even low light levels become excessive and zeaxanthin-related photoprotection is engaged. We speculate that these processes, as well as stem curling and self shading (Eickmeier et al. 1992), serve to minimize photoinhibitory damage toS. lepidophylla during the process of dehydration.