Boea Hygrometrica Research Articles

A comparative study on Ca content and distribution in two Gesneriaceae species reveals distinctive mechanisms to cope with high rhizospheric soluble calcium.

Excessive Ca is toxic to plants thus significantly affects plant growth and species distribution in Ca-rich karst areas. To understand how plants survive high Ca soil, laboratory experiments were established to compare the physiological responses and internal Ca distribution in organ, tissue, cell, and intracellular levels under different Ca levels for Lysionotus pauciflorus and Boea hygrometrica, two karst habitant Gesneriaceae species in Southwest China. In the controlled condition, L. pauciflorus could survive as high as 200 mM rhizospheric soluble Ca, attributed to a series of physiological responses and preferential storage that limited Ca accumulation in chloroplasts of palisade cells. In contrast, B. hygrometrica could survive only 20 mM rhizospheric soluble Ca, but accumulated a high level of internal Ca in both palisade and spongy cells without disturbance on photosynthetic activity. By phenotype screening of transgenic plants expressing high Ca-inducible genes from B. hygrometrica, the expression of BhDNAJC2 in A. thaliana was found to enhance plant growth and photosynthesis under high soluble Ca stress. BhDNAJC2 encodes a recently reported heat shock protein (HSP) 40 family DnaJ-domain protein. The Ca-resistant phenotype of BhDNAJC2 highlights the important role of chaperone-mediated protein quality control in Ca tolerance in B. hygrometrica. Taken together, our results revealed that distinctive mechanisms were employed in the two Gesneriaceae karst habitants to cope with a high Ca environment.

Identification of a retroelement from the resurrection plant Boea hygrometrica that confers osmotic and alkaline tolerance in Arabidopsis thaliana.

Functional genomic elements, including transposable elements, small RNAs and non-coding RNAs, are involved in regulation of gene expression in response to plant stress. To identify genomic elements that regulate dehydration and alkaline tolerance in Boea hygrometrica, a resurrection plant that inhabits drought and alkaline Karst areas, a genomic DNA library from B. hygrometrica was constructed and subsequently transformed into Arabidopsis using binary bacterial artificial chromosome (BIBAC) vectors. Transgenic lines were screened under osmotic and alkaline conditions, leading to the identification of Clone L1-4 that conferred osmotic and alkaline tolerance. Sequence analyses revealed that L1-4 contained a 49-kb retroelement fragment from B. hygrometrica, of which only a truncated sequence was present in L1-4 transgenic Arabidopsis plants. Additional subcloning revealed that activity resided in a 2-kb sequence, designated Osmotic and Alkaline Resistance 1 (OAR1). In addition, transgenic Arabidopsis lines carrying an OAR1-homologue also showed similar stress tolerance phenotypes. Physiological and molecular analyses demonstrated that OAR1-transgenic plants exhibited improved photochemical efficiency and membrane integrity and biomarker gene expression under both osmotic and alkaline stresses. Short transcripts that originated from OAR1 were increased under stress conditions in both B. hygrometrica and Arabidopsis carrying OAR1. The relative copy number of OAR1 was stable in transgenic Arabidopsis under stress but increased in B. hygrometrica. Taken together, our results indicated a potential role of OAR1 element in plant tolerance to osmotic and alkaline stresses, and verified the feasibility of the BIBAC transformation technique to identify functional genomic elements from physiological model species.

Molecular cloning and differential expression of sHSP gene family members from the resurrection plant Boea hygrometrica in response to abiotic stresses

AbstractSmall heat shock proteins (sHSPs) are a class of molecular chaperones that bind to and prevent aggregation of proteins. To assess the potential role of sHSPs in protection against abiotic stresses, we conducted a screening of sHSP genes from the desiccation-tolerant resurrection plant Boea hygrometrica, which is widespread in East Asia in alkaline, calcium-rich limestone crevices. In total, 25 sHSP genes, belonging to six subgroups, were identified from the desiccated leaves of B. hygrometrica. Ten of these genes were cloned and named according to the nomenclature proposed for sHSPs. Transcripts of all these BhsHSPs were detectable in fresh leaves, but only 6 genes were induced after desiccation, and remained high during rehydration. Four of the cytosol-targeted BhsHSP genes were up-regulated under treatments, such as heat, cold, alkaline conditions, high calcium, oxidation, or application of the phytohormone abscisic acid. Together, these results demonstrate that CI and CII sHSPs, especially Bh17.9CI and Bh17.4BCII, are associated with abiotic stresses, and may function in the maintenance of protein stability, aiding in the adaptations to extreme environmental conditions in which B. hygrometrica can survive.

Understanding desiccation tolerance using the resurrection plant Boea hygrometrica as a model system.

Vegetative tissues of Boea hygrometrica, a member of the Gesneriaceae family, can tolerate severe water loss to desiccated state and fully recover upon rehydration. Unlike many other so called “resurrection plants,” the detached leaves of B. hygrometrica also possess the same level of capacity for desiccation tolerance (DT) as that of whole plant. B. hygrometrica is distributed widely from the tropics to northern temperate regions in East Asia and grows vigorously in areas around limestone rocks, where dehydration occurs frequently, rapidly, and profoundly. The properties of detached B. hygrometrica leaves and relative ease of culture have made it a useful system to study the adaptive mechanisms of DT. Extensive studies have been conducted to identify the physiological, cellular, and molecular mechanisms underlying DT in the last decade, including specific responses to water stress, such as cell wall folding and pigment-protein complex stabilizing in desiccated leaves. In this review, the insight into the structural, physiological, and biochemical, and molecular alterations that accompany the acquisition of DT in B. hygrometrica is described. Finally a future perspective is proposed, with an emphasis on the emerging regulatory roles of retroelements and histone modifications in the acquisition of DT, and the need of establishment of genome sequence database and high throughput techniques to identify novel regulators for fully understanding of the matrix of DT.

The Complete Chloroplast and Mitochondrial Genome Sequences of Boea hygrometrica: Insights into the Evolution of Plant Organellar Genomes

The complete nucleotide sequences of the chloroplast (cp) and mitochondrial (mt) genomes of resurrection plant Boea hygrometrica (Bh, Gesneriaceae) have been determined with the lengths of 153,493 bp and 510,519 bp, respectively. The smaller chloroplast genome contains more genes (147) with a 72% coding sequence, and the larger mitochondrial genome have less genes (65) with a coding faction of 12%. Similar to other seed plants, the Bh cp genome has a typical quadripartite organization with a conserved gene in each region. The Bh mt genome has three recombinant sequence repeats of 222 bp, 843 bp, and 1474 bp in length, which divide the genome into a single master circle (MC) and four isomeric molecules. Compared to other angiosperms, one remarkable feature of the Bh mt genome is the frequent transfer of genetic material from the cp genome during recent Bh evolution. We also analyzed organellar genome evolution in general regarding genome features as well as compositional dynamics of sequence and gene structure/organization, providing clues for the understanding of the evolution of organellar genomes in plants. The cp-derived sequences including tRNAs found in angiosperm mt genomes support the conclusion that frequent gene transfer events may have begun early in the land plant lineage.

Cloning and Expression of a Gene Encoding a Raffinose Synthase in the Resurrection Plant <I>Boea hygrometrica</I>

Cloning and Expression of a Gene Encoding a Raffinose Synthase in the Resurrection Plant <I>Boea hygrometrica</I>

Chemical Constituents of Boea hygrometrica

Aim To study the chemical constituents of Boea hygrometrica (Bunge.) R. Br. Methods The compounds were isolated and purified by Diaion HP-20, Toyopearl HW-40, silica gel column chromatography and the structures were identified on the basis of spectral data and physiochemical properties. Results Seven compounds were obtained and identified as 5,7,3′4′-tetrahydroxy-6-methoxy-8- C-[β-D-xylopyranosy1-(1→2)]-β-D-glucopyranosyl flavone ( 1), p-hydroxy phenethylalcohol ( 2), 3,4-dihydroxy phenethylalcohol ( 3), apocynin ( 4), ferulic acid ( 5), 1′- O-β-D-(3,4-dihydroxy)-ethyl-6′- O-trans-caffeoyl-β-D-apiofuranosyl-(1→3′)- glucopyranoside ( 6), gentisic acid ( 7). Conclusion Compound 1 was a new c-glycoside flavonal and compounds 2–7 were isolated from this plant for the first time.

An efficient procedure for plant organellar genome assembly, based on whole genome data from the 454 GS FLX sequencing platform

MotivationComplete organellar genome sequences (chloroplasts and mitochondria) provide valuable resources and information for studying plant molecular ecology and evolution. As high-throughput sequencing technology advances, it becomes the norm that a shotgun approach is used to obtain complete genome sequences. Therefore, to assemble organellar sequences from the whole genome, shotgun reads are inevitable. However, associated techniques are often cumbersome, time-consuming, and difficult, because true organellar DNA is difficult to separate efficiently from nuclear copies, which have been transferred to the nucleus through the course of evolution.ResultsWe report a new, rapid procedure for plant chloroplast and mitochondrial genome sequencing and assembly using the Roche/454 GS FLX platform. Plant cells can contain multiple copies of the organellar genomes, and there is a significant correlation between the depth of sequence reads in contigs and the number of copies of the genome. Without isolating organellar DNA from the mixture of nuclear and organellar DNA for sequencing, we retrospectively extracted assembled contigs of either chloroplast or mitochondrial sequences from the whole genome shotgun data. Moreover, the contig connection graph property of Newbler (a platform-specific sequence assembler) ensures an efficient final assembly. Using this procedure, we assembled both chloroplast and mitochondrial genomes of a resurrection plant, Boea hygrometrica, with high fidelity. We also present information and a minimal sequence dataset as a reference for the assembly of other plant organellar genomes.

Two new C-glycosylflavones from Boea hygrometrica

Two new C-glycosylflavones, named 5,7,3′,4′-tetrahydroxy-6-methoxy-8-C-β-D-gluco-pyranosyl flavonoside (1), 5,3′,4′-trihydroxy-6,7-dimethoxy-8-C-[β-D-apiofuranosyl-(1 → 2)]-β-D-glucopyranosyl flavonoside (2), together with nine known compounds (3–11), were isolated from 50% acetone extract of Boea hygrometrica (Bunge.) R.Br. Their structures were established by spectroscopic techniques including MS, IR, UV, and 2D NMR.

A role for a cell wall localized glycine‐rich protein in dehydration and rehydration of the resurrection plant Boea hygrometrica

The acquisition of desiccation tolerance in dicotyledonous angiosperms requires the induction of a co-ordinated programme of genetic and biochemical processes during drying and the adaptive mechanisms are primarily protoplasmic in nature. Recent studies have shown that changes in cell wall structure and composition are also important for recovery after drying, however, the molecular mechanisms that underpin these adaptive responses are largely unknown. Here, the desiccation-tolerant plant Boea hygrometrica was used as a model system to investigate the changes in gene expression and cell wall adaptation that take place during extreme dehydration. A cDNA macroarry analysis of dehydration-inducible genes led to the identification of a gene encoding a glycine-rich protein (BhGRP1). The corresponding transcript was up-regulated during drying in B. hygrometrica leaves. In silico analysis revealed that BhGRP1 is targeted to the cell wall and this was confirmed in planta. Morphological changes in the cell wall architecture were also observed during the process of drying and re-watering. Concomitant with this observation, cell wall profiling by Fourier transform infrared spectroscopy indicated that protein levels increased upon desiccation and remained broadly similar upon re-watering. These findings suggest that the deposition of BhGRP1 may play a role in cell wall maintenance and repair during dehydration and rehydration in B. hygrometrica.

A WRKY transcription factor participates in dehydration tolerance in Boea hygrometrica by binding to the W-box elements of the galactinol synthase (BhGolS1) promoter

Accumulation of compatible osmolytes, such as soluble sugars, in plants is an important osmoprotective mechanism. Sugars play a role in osmotic adjustment and are associated with stabilization of proteins and cell structures, reactive oxygen species scavenging, signaling functions or induction of adaptive pathways. Galactinol is the galactosyl donor for the synthesis of raffinose family oligosaccharides (RFOs) and its synthesis by galactinol synthase (GolS) is the first committed step of the RFOs biosynthetic pathway. GolS genes are induced by a variety of stresses in both stress-sensitive and tolerant-plant species; however, the mechanism of transcriptional regulation is not fully established. In this paper, we characterized a GolS gene (BhGolS1) that was dehydration and ABA-inducible in the resurrection plant Boea hygrometrica and conferred dehydration tolerance in a transgenic tobacco system. Four W-box cis-elements were identified in the BhGolS1 promoter and shown to be bound by an early dehydration and ABA-inducible WRKY gene (BhWRKY1). These data suggest a mechanism where BhWRKY1 is likely to function in an ABA-dependent signal pathway to regulate BhGolS1 expression, which leads to the accumulation of RFOs in desiccation-tolerant B. hygrometrica leaves.

Ectopic over-expression of BhHsf1, a heat shock factor from the resurrection plant Boea hygrometrica, leads to increased thermotolerance and retarded growth in transgenic Arabidopsis and tobacco

Plant heat shock transcription factors (Hsfs) are commonly found to be involved in various stress responses. Several Hsfs displayed dwarf phenotype while conferred stress tolerance when over-expressed. However, the underlying mechanisms were not fully understood. Here we report the cloning and characterization of an Hsf (BhHsf1) from the resurrection plant Boea hygrometrica. Drought, heat and wound can induce BhHsf1 expression. The over-expression of BhHsf1 conferred growth retardation and stress tolerance in both Arabidopsis and tobacco. Evidence was presented to show that the growth retardation of aerial organs in the transgenic plants was resulted from the reduction of cell proliferation. Gene expression profiling using microarray hybridization and pathway analysis showed that Hsps and stress-associated genes were induced whereas the genes related to DNA replication and mitotic cell cycle were down-regulated in BhHsf1 over-expression Arabidopsis, which was in consistence with the observation of the impaired nuclear endoreduplication. Taking together, our results suggest that BhHsf1 may play dual roles in mediating the processes in heat stress tolerance and growth retardation via regulation of target genes related to stress protection and mitotic cell cycle.

Cloning and expression analysis of a dirigent protein gene from the resurrection plant Boea hygrometrica

Resurrection plants are tolerant to extreme dehydration and are useful model systems to study genes that play a role in drought tolerance. A gene fragment encoding a dirigent protein that is predicted to function in lignin biosynthesis was identified from leaves of the resurrection plant Boea hygrometrica via cDNA microarray screening. A cDNA, designated BhDIR1, containing the complete predicted open reading frame, was obtained by 5′-RACE. BhDIR1 transcripts were found to be accumulated in response to changes in plant dehydration status, exogenously applied phytohormones and signaling molecules, and temperature stresses. BhDIR1 encodes a protein of 199 amino acids, which shows 20–40% similarity to dirigent proteins reported from other plants. BhDIR1 is predicted to contain a cleavable signal peptide at the N-terminal, and its plasma membrane/cell wall localization was confirmed using a GFP fusion protein assay. Consistent with this discovery, the acid-soluble lignin content decreased in dehydrated B. hygrometrica leaves . Taken together, our results indicate a protective role for a dirigent protein in response to drought stress by changing the physical characters of lignin which in turn is predicted to affect the mechanical strength and flexibility of the plant cell wall.

LEA 4 group genes from the resurrection plant Boea hygrometrica confer dehydration tolerance in transgenic tobacco

The resurrection plant Boea hygrometrica can survive extreme dehydration and is used as a model system to study desiccation tolerance. Screening of a cDNA library prepared from desiccated leaves via a macroarray technique has resulted in the identification of two dehydration responsive genes that encode group 4 late embryogenesis abundant (LEA) proteins, designated as BhLEA1 and BhLEA2, respectively. BhLEA1 and BhLEA2 were induced by dehydration and signaling molecules, including abscisic acid (ABA). Transgenic tobacco that ectopically express BhLEA1 and BhLEA2 were generated and used to study the role of LEA proteins in dehydration tolerance. After a period of drought, the relative water content of leaves and photosystem II activity in transgenic tobacco were higher than wild-type plants. Furthermore the membrane permeability was lower in selected transgenic lines that expressed BhLEA1 and BhLEA2 than in wild-type plants. Superoxide dismutase and peroxidase activities were increased in transgenic plants relative to that observed in the wild-type control and proteins including ribulose-bisphosphate carboxylase (large subunit), light-harvesting complex II and photosystem II extrinsic protein were stabilized in transgenic plants compared to wild-type plants. Surprisingly, the steady state levels of BhLEA1 and BhLEA2 protein substantially increased in response drying, despite being under the transcriptional control of the CaMV 35S promoter. Data presented here suggests that BhLEA genes are likely to play a role in the general protection of the plant cell during dehydration and affect membrane and protein stability.

Proteome analysis of leaves from the resurrection plant Boea hygrometrica in response to dehydration and rehydration

Resurrection plants differ from other species in their unique ability to survive desiccation. In order to understand the mechanisms of desiccation tolerance, proteome studies were carried out using leaves of the resurrection plant Boea hygrometrica to reveal proteins that were differentially expressed in response to changes in relative water content. This opportunity was afforded by the rare ability of excised B. hygrometrica leaves to survive and resume metabolism following desiccation in a manner similar to intact plants. From a total of 223 proteins that were reproducibly detected and analyzed, 35% showed increased abundance in dehydrated leaves, 5% were induced in rehydrated leaves and 60% showed decreased or unchanged abundance in dehydrated and rehydrated leaves. Since the induction kinetics fall into clearly defined patterns, we suggest that programmed regulation of protein expression triggered by changes of water status. Fourteen dehydration responsive proteins were analyzed by mass spectrometry. Eight proteins were classified as playing a role in reactive oxygen species scavenging, photosynthesis and energy metabolism. In agreement with these findings, glutathione content and polyphenol oxidase activity were found to increase upon dehydration and rapid recovery of photosynthesis was observed.

A comparison of photosynthetic apparatus of the detached leaves of the resurrection plant Boea hygrometrica with its non-tolerant relative Chirita heterotrichia in response to dehydration and rehydration

Comparisons of the water contents in detached leaves of Boea hygrometrica (Bunge) R. Br ., and other members of the family Gesneriaceae have shown that B. hygrometrica can tolerate an extraordinarily high degree of water loss and restore its life upon rehydration. We have investigated the effects of dehydration on photosynthetic function in B. hygrometrica in comparison with its non-resurrection relative Chirita heterotrichia Merr. Studies on the net photosynthetic rate, chlorophyll fluorescence emission and excitation spectra, and the kinetics of chlorophyll fluorescence induction revealed that the effects of dehydration on both species were similar insofar as photosystem II was more sensitive to dehydration than photosystem I. However, B. hygrometrica responded more rapidly than C. heterotrichia. Although photosynthetic activity could be restored in both species upon rehydration after 2 days of dehydration, only B. hygrometrica recovered when the dehydration period was extended to 8 days. In contrast to C. heterotrichia leaves, in which the levels of carotenoids decreased rapidly during desiccation, carotenoid content actually increased in B. hygrometrica leaves upon dehydration and returned to the normal level after rehydration. Non-denaturing electrophoresis revealed that the thylakoid pigment–protein complexes of B. hygrometrica were highly stable during desiccation and rehydration, whereas those of C. heterotrichia were totally destroyed after 8 days of desiccation.