Boea Hygrometrica Research Articles

Structure and dynamics of microbial communities associated with the resurrection plant Boea hygrometrica in response to drought stress.

The resurrection plant Boea hygrometrica selectively recruits and assembles drought-specific microbial communities across the plant-soil compartments, which may benefit plant growth and fitness under extreme drought conditions. Plant-associated microbes are essential for facilitating plant growth and fitness under drought stress. The resurrection plant Boea hygrometrica in natural habitats with seasonal rainfall can survive rapid desiccation, yet their interaction with microbiomes under drought conditions remains unexplored. This study examined the bacterial and fungal microbiome structure and drought response across plant-soil compartments of B. hygrometrica by high-throughput amplicon sequencing of 16S rRNA gene and internal transcribed spacer. Our results demonstrated that the diversity, composition, and functional profile of the microbial community varied considerably across the plant-soil compartments and were strongly affected by drought stress. Bacterial and fungal diversity was significantly reduced from soil to endosphere and belowground to aboveground compartments. The compartment-specific enrichment of the dominant bacteria phylum Cyanobacteriota and genus Methylorubrum in leaf endosphere, genera Pseudonocardia in rhizosphere soil and Actinoplanes in root endosphere, and fungal phylum Ascomycota in the aboveground compartments and genera Knufia in root endosphere and Cladosporium in leaf endosphere composed part of the core microbiota with corresponding enrichment of beneficial functions for plant growth and fitness. Moreover, the recruitment of dominant microbial genera Sphingosinicella and Plectosphaerella, Ceratobasidiaceae mycorrhizal fungi, and numerous plant growth-promoting bacteria involving nutrient supply and auxin regulation was observed in desiccated B. hygrometrica plants. Our results suggest that the stable assembled drought-specific microbial community of B. hygrometrica may contribute to plant survival under extreme environments and provide valuable microbial resources for the microbe-mediated drought tolerance enhancement in crops.

Mitochondrial genome characteristics and phylogenetic analysis of the medicinal and edible plant Mesona chinensis Benth.

Mesona chinensis Benth (MCB) (or Platostoma palustre or Platostoma chinense) is an important edible and medicinal plant in China. However, the mitochondrial genome (mitogenome, or mtDNA) of MCB has not been characterized or reported yet. In this study, we first sequenced and characterized the complete mitogenome of MCB. The MCB mitogenome was 494,599bp in length and encoded 59 genes containing 37 protein-coding genes (PCGs), 19 tRNAs, and 3 rRNAs. Gene transfer analysis revealed that a total of 12 transfer segments with more than 93% identity (total length of 25,427bp) were detected in the MCB mitogenome. Simple sequence repeats (SSR) analysis showed that 212 simple sequence repeats (SSR) were identified. Repeat sequence analysis revealed 305 repeat sequences (158 forward and 147 palindromic repeats) ranging from 30bp to 48,383bp and the 30-39bp repeats were the majority type. Relative synonymous codon usage (RSCU) analysis uncovered that in total, 9,947 codons were encoding the protein-coding genes (PCGs). Serine (909, 9.1%) and leucine (879, 8.8%) were the two most abundant amino acids, while terminator (32, .3%) was the least abundant amino acid. Ka/Ks analysis indicated that almost all genes were subject to purification selection, except ccmB. Analysis of Lamiaceae mitogenomes constitution revealed that atpB and atpE were unique to the Rotheca serrata and Salvia miltiorrhiza mitogenomes. mttB gene loss was unique to the Boea hygrometrica mitogenome. The core fragments of the Lamiaceae mitogenomes harbored a higher GC content than the specific and variable fragments. In addition, phylogenetic analysis revealed that MCB was closely related to Salvia miltiorrhiza based on the mitogenomes. The current study provided valuable genomic resources for understanding and utilizing this important medicinal plant in the future.

Whole genome and transcriptome reveal flavone accumulation in Scutellaria baicalensis roots.

Scutellaria baicalensis Georgi is a medicinal plant in the Lamiaceae family that contains high levels of 4'-deoxyflavone and other flavonoids in its roots. Therefore, it has strong potential as a plant resource for researching the biosynthesis of specific flavonoids. In this study, we report on a chromosome-level S. baicalensis genome assembled to nine chromosomes (376.81M) using PacBio, HiSeq XTen, and Hi-C assisted assembly. The assembly ratio was 99.22%, the contig N50 was 1.80 million bases, and the scaffold N50 was 40.57 million bases, with 31896 genes being annotated. Comparative genome analysis revealed that S. baicalensis and Salvia miltiorrhiza belonged to the same branch, and diverged 36.3 million years ago. Other typically correlated species were Boea hygrometrica and Sesamum indicum. We investigated the structural genes involved in flavonoid synthesis in combination with transcriptome sequencing analysis for different tissues (roots, stems, flowers, leaves) of purple, pink, and white flowers. The results revealed that S.baiF6H is involved in the accumulation of baicalein and was significantly increased in both purple roots vs. pink roots and white roots vs. pink roots. S.baiMYB gene family expression pattern analysis and co-expression network analysis revealed that S.baiMYB transcription factors primarily regulated the production of flavonoids in S. baicalensis. S.baiMYB serves as a major factor regulating flavonoid synthesis in the roots, where yeast one-hybrid assays revealed that these transcription factors could bind to the promoter regions of structural genes to control the accumulation of flavonoids. Genome and transcriptome sequencing, co-expression analysis, and yeast one-hybrid experiments provided valuable genetic resources for understanding flavonoid biosynthesis in S. baicalensis. These findings contribute to a better understanding of the accumulation of metabolites in Lamiaceae.

Research of Water Molecules Cluster Structuring during Haberlea rhodopensis Friv. Hydration

Gesneriaceae plant family is comprised of resurrection species, namely Boea hygrometrica and Paraboea rufescens, that are native to the Southeast Asia and Haberlea rhodopensis, Ramonda myconi, and Ramonda serbica, which are mainly found in the Balkan Peninsula. Haberlea rhodopensis is known to be able to survive extreme and prolonged dehydration. Study was carried out after the dried plant Haberlea rhodopensis Friv. had been hydrated and had reached its fresh state. Two juice samples were collected from the plant blossom: The first sample was prepared with 1% filtered water through a patented EVOdrop device. Then the sample was saturated with hydrogen with EVOdrop booster to a concentration of 1.2 ppm, pH = 7.3, ORP = −390 mV. This first sample was prepared with filtered tap water from Sofia, Bulgaria. The second sample, which was a control one, was developed with tap water from Sofia, Bulgaria, consisting of 1% solutions of Haberlea rhodopensis. A study revealed that during the drying process in H. rhodopensis the number of free water molecules decreases, and water dimers are formed. The aim of our study was to determine the number of water molecules in clusters in 1% solutions of hydrated H. rhodopensis plants. Results were analyzed according to the two types of water used in the experiment. Th EVOdrop device is equipped with an ultranano membrane and rotating jet nozzle to create a vortex water and saturation thanks to a second device EVObooster to obtain hydrogen-rich water. In the current study Hydrogen-rich water is referred to as Hydrogen EVOdrop Water (HEW). Research was conducted using the following methods—spectral methods non-equilibrium energy spectrum (NES) and differential non-equilibrium energy spectrum (DNES), mathematical models, and study of the distribution of water molecules in water clusters. In a licensed Eurotest Laboratory, the research of tap water before and after flowing through the EVOdrop device was proven. Studies have been carried out on the structuring of water molecule clusters after change of hydrogen bond energies. The restructuring comes with rearrangement of water molecules by the energy levels of hydrogen bonds. Local extrema can be observed in the spectrum with largest amount of water molecules. The structural changes were tested using the NES and DNES spectral methods. The conducted research proved that the application of EVOdrop device and EVObooster changes the parameters of water to benefit hydration and health.

Genome-wide identification of CrRLK1L gene family and desiccation-induced expression profiles in Boea hygrometrica

Catharanthus roseus receptor-like kinase 1-like (CrRLK1L) proteins constitute a subfamily of receptor-like kinases (RLKs) that play diverse roles during fertilization, vegetative development and plant pathogen interactions. CrRLK1Ls possess a unique malectin-like domain at N-terminal that bind to oligo- or polysaccharides from cell wall polymers, byproducts of cell wall degradation, or membrane-associated or secreted glycosylated proteins. CrRLK1L members have been identified in many organisms, however, the study of this gene family in resurrection plant species has not been reported to date. Resurrection plants are a kind of extremophiles that can survive extreme drought stress (desiccation) and recover rapidly after rehydration, and display specific and reversible cell wall structure and component changes during dehydration and rehydration. Here, we identified 18 CrRLK1L protein members in the resurrection plant Boea hygrometrica genome and classified them into 9 clades based on the conserved amino acid sequences. Phylogenetic analysis reveals the expansion of FER clade, the absence of MEDOS and CVY clades and the emergence of a new Bh-specific clade in BhCrRLK1L protein family. Analysis of cis-regulatory elements has predicted several types of drought induced elements and/or drought related hormone responsiveness elements in the promoter regions of all BhCrRLK1Ls. In agreement, we found 15 members of BhCrRLK1Ls change their expression pattern in response to drought stress, based on a previous transcriptome survey. Subsequent qRT-PCR validation of selected 7 BhCrRLK1L genes confirmed that BhFER1, BhCrRLK1L14 and BhCrRLK1L15 are induced by desiccation, and BhFER3, BhCrRLK1L17 and BhCrRLK1L18 are repressed by desiccation. Our study systematically identified the CrRLK1L members in B. hygrometrica, and analyzed the gene expression profiles in response to desiccation stresses, which lays a foundation for exploring the function of BhCrRLK1Ls in desiccation signal transduction in B. hygrometrica.

Sequence Analysis of the Complete Mitochondrial Genome of a Medicinal Plant, Vitex rotundifolia Linnaeus f. (Lamiales: Lamiaceae).

In the present study, we depicted the complete mitochondrial genome of a valuable medicinal plant, Vitex rotundifolia. The mitochondrial genome of V. rotundifolia, mapped as a circular molecule, spanned 380,980 bp in length and had a GC content of 45.54%. The complete genome contained 38 protein-coding genes, 19 transfer RNAs (tRNAs), and 3 ribosomal RNAs (rRNAs). We found that there were only 38.73% (147.54 kb), 36.28% (138.23 kb), and 52.22% (198.96 kb) of the homologous sequences in the mitochondrial genome of V. rotundifolia, as compared with the mitochondrial genomes of Scutellaria tsinyunensis, Boea hygrometrica, and Erythranthe lutea, respectively. A multipartite structure mediated by the homologous recombinations of the three direct repeats was found in the V. rotundifolia mitochondrial genome. The phylogenetic tree was built based on 10 species of Lamiales, using the maximum likelihood method. Moreover, this phylogenetic analysis is the first to present the evolutionary relationship of V. rotundifolia with the other species in Lamiales, based on the complete mitochondrial genome.

Two Decades of Desiccation Biology: A Systematic Review of the Best Studied Angiosperm Resurrection Plants.

Resurrection plants have an extraordinary ability to survive extreme water loss but still revive full metabolic activity when rehydrated. These plants are useful models to understand the complex biology of vegetative desiccation tolerance. Despite extensive studies of resurrection plants, many details underlying the mechanisms of desiccation tolerance remain unexplored. To summarize the progress in resurrection plant research and identify unexplored questions, we conducted a systematic review of 15 model angiosperm resurrection plants. This systematic review provides an overview of publication trends on resurrection plants, the geographical distribution of species and studies, and the methodology used. Using the Preferred Reporting Items for Systematic reviews and Meta–Analyses protocol we surveyed all publications on resurrection plants from 2000 and 2020. This yielded 185 empirical articles that matched our selection criteria. The most investigated plants were Craterostigma plantagineum (17.5%), Haberlea rhodopensis (13.7%), Xerophyta viscosa (reclassified as X. schlechteri) (11.9%), Myrothamnus flabellifolia (8.5%), and Boea hygrometrica (8.1%), with all other species accounting for less than 8% of publications. The majority of studies have been conducted in South Africa, Bulgaria, Germany, and China, but there are contributions from across the globe. Most studies were led by researchers working within the native range of the focal species, but some international and collaborative studies were also identified. The number of annual publications fluctuated, with a large but temporary increase in 2008. Many studies have employed physiological and transcriptomic methodologies to investigate the leaves of resurrection plants, but there was a paucity of studies on roots and only one metagenomic study was recovered. Based on these findings we suggest that future research focuses on resurrection plant roots and microbiome interactions to explore microbial communities associated with these plants, and their role in vegetative desiccation tolerance.

DNA methylation-mediated modulation of rapid desiccation tolerance acquisition and dehydration stress memory in the resurrection plant Boea hygrometrica.

Pre-exposure of plants to various abiotic conditions confers improved tolerance to subsequent stress. Mild drought acclimation induces acquired rapid desiccation tolerance (RDT) in the resurrection plant Boea hygrometrica, but the mechanisms underlying the priming and memory processes remain unclear. In this study, we demonstrated that drought acclimation-induced RDT can be maintained for at least four weeks but was completely erased after 18 weeks based on a combination of the phenotypic and physiological parameters. Global transcriptome analysis identified several RDT-specific rapid dehydration-responsive genes related to cytokinin and phospholipid biosynthesis, nitrogen and carbon metabolism, and epidermal morphogenesis, most of which were pre-induced by drought acclimation. Comparison of whole-genome DNA methylation revealed dehydration stress-responsive hypomethylation in the CG, CHG, and CHH contexts and acclimation-induced hypermethylation in the CHH context of the B. hygrometrica genome, consistent with the transcriptional changes in methylation pathway genes. As expected, the global promoter and gene body methylation levels were negatively correlated with gene expression levels in both acclimated and dehydrated plants but showed no association with transcriptional divergence during the procedure. Nevertheless, the promoter methylation variations in the CG and CHG contexts were significantly associated with the differential expression of genes required for fundamental genetic processes of DNA conformation, RNA splicing, translation, and post-translational protein modification during acclimation, growth, and rapid dehydration stress response. It was also associated with the dehydration stress-induced upregulation of memory genes, including pre-mRNA-splicing factor 38A, vacuolar amino acid transporter 1-like, and UDP-sugar pyrophosphorylase, which may contribute directly or indirectly to the improvement of dehydration tolerance in B. hygrometrica plants. Altogether, our findings demonstrate the potential implications of DNA methylation in dehydration stress memory and, therefore, provide a molecular basis for enhanced dehydration tolerance in plants induced by drought acclimation.

MicroRNA profiling the resurrection plant Haberlea rhodopensis unveils essential regulators of survival under severe drought

Small RNAs (sRNAs) are essential components of gene-regulatory networks, which guide plant development and tune it to environmental challenges. Though the past years have witnessed evidences on sRNA importance for stress response, there is scarce data on their involvement in resurrection plant survival under severe drought. Haberlea rhodopensis (hrh) is an angiosperm resurrection species, whose vegetative tissues can tolerate desiccation and recover upon rehydration. In this study, high-throughput sequencing sRNAs indicated a higher complexity of the sRNA population, especially of a 24 nt sRNA category, in the desiccated vegetative tissue of H. rhodopensis compared to unstressed tissues. The cross-species discovery was performed to predict 77 mature microRNAs (miRNAs), most of which were assigned to 23 high-confidence conserved miRNA families in the leaf tissue. Several members of the miR156/157, miR166, and miR399 families were found to be desiccation-responsive. The miR156/157 family members were found up-regulated upon dehydration and down-regulated upon rehydration, while the miR166 and miR399 family members followed an opposite trend of expression. A probable miR156/157 target, orthologous to the SQUAMOSA promoter binding protein-like, was reconstructed in H. rhodopensis based on genomic data available for this species and the closely related Boea hygrometrica. Reverse transcription quantittative PCR analysis confirmed the expression profile of hrh-miR156a-5p and hrh-miR157-5p established by sRNA sequencing and revealed an inverse expression pattern between these miRNAs and their targets in the desiccated tissue. Our study suggests that the miR156/157 and miR399 families are essential for plant survival under severe drought due to their ability to control plant development and growth by modulating transcription factor expression.

Discover the Dehydration Response Genes in <i>Boea hygrometrica</i> Transcriptome Using Bayesian Network Approach

“Drying without dying” is an amazing feature in land plant evolution. <i>Boea hygrometrica</i> is an important resurrection plant model. The current genome and transcriptome analysis have revealed that some biological processes may contribute to its dehydration tolerance, but genes play pivotal roles in the dehydration response remains unclear. Bayesian network approach is a powerful tool for transcriptome data analysis and biological network reconstruction. In this work, by using the Bayesian network approach, we first reconstruct a gene regulation network with the <i>B. hygrometrica</i> transcriptome data. The network contains 1292 genes. Next, we defined the hub node genes in the network and focus on their functions in order to understand the response <i>B. hygrometrica</i> carried out under the dehydration stress. Finally, by an association analysis, we deduce the function of the unknown gene <i>Bhs126_021</i> which has a degree of 84 in the network. The data-driven strategy we applied in this work not only finds out the knowledge from the knowledge-driven strategy analysis, but also provides novel findings from the <i>B. hygrometrica</i> transcriptome. Our findings give insight of control genes in land plant under the dehydration stress. The data-driven strategy applied in this work can also efficiently analyze other similar transcriptome data sets.

Common and Specific Mechanisms of Desiccation Tolerance in Two Gesneriaceae Resurrection Plants. Multiomics Evidences.

Environmental stress, especially water deficiency, seriously limits plant distribution and crop production worldwide. A small group of vascular angiosperm plants termed “resurrection plants,” possess desiccation tolerance (DT) to withstand dehydration and to recover fully upon rehydration. In recent years, with the rapid development of life science in plants different omics technologies have been widely applied in resurrection plants to study DT. Boea hygrometrica is native in East and Southeast Asia, and Haberlea rhodopensis is endemic to the Balkans in Europe. They are both resurrection pants from Gesneriaceae family. This paper reviews recent advances in transcriptome and metabolome, and discusses the differences and similarities of DT features between both species. Finally, we believe we provide novel insights into understanding the mechanisms underlying the acquisition and evolution of desiccation tolerance of the resurrection plants that could substantially contribute to develop new approaches for agriculture to overcome water deficiency in future.

Weighted Gene Co-expression Network Analysis (WGCNA) Reveals the Hub Role of Protein Ubiquitination in the Acquisition of Desiccation Tolerance in Boea hygrometrica.

Boea hygrometrica can survive extreme drought conditions and has been used as a model to study desiccation tolerance. A genome-wide transcriptome analysis of B. hygrometrica showed that the plant can survive rapid air-drying after experiencing a slow soil-drying acclimation phase. In addition, a weighted gene co-expression network analysis was used to study the transcriptomic datasets. A network comprising 22 modules was constructed, and seven modules were found to be significantly related to desiccation response using an enrichment analysis. Protein ubiquitination was observed to be a common process linked to hub genes in all the seven modules. Ubiquitin-modified proteins with diversified functions were identified using immunoprecipitation coupled with mass spectrometry. The lowest level of ubiquitination was noted at the full soil drying priming stage, which coincided the accumulation of dehydration-responsive gene BhLEA2. The highly conserved RY motif (CATGCA) was identified from the promoters of ubiquitin-related genes that were downregulated in the desiccated samples. An in silico gene expression analysis showed that the negative regulation of ubiquitin-related genes is potentially mediated via a B3 domain-containing transcription repressor VAL1. This study suggests that priming may involve the transcriptional regulation of several major processes, and the transcriptional regulation of genes in protein ubiquitination may play a hub role to deliver acclimation signals to posttranslational level in the acquisition of desiccation tolerance in B. hygrometrica.

A role of age-dependent DNA methylation reprogramming in regulating the regeneration capacity of Boea hygrometrica leaves.

Plants can regenerate new individuals under appropriate culture conditions. Although the molecular basis of shoot regeneration has steadily been unraveled, the role of age-dependent DNA methylation status in the regulation of explant regeneration remains practically unknown. Here, we established an effective auxin/cytokinin-induced shoot regeneration system for the resurrection plant Boea hygrometrica via direct organogenesis and observed that regeneration was postponed with increasing age of donor plants. Global transcriptome analysis revealed significant upregulation of genes required for hormone signaling and phenylpropanoid biosynthesis and downregulation of photosynthetic genes during regeneration. Transcriptional changes in the positive/negative regulators and cell wall-related proteins involved in plant regeneration, such as ELONGATED HYPOCOTYL5 (HY5), LATERAL ORGAN BOUNDARIES DOMAIN, SHOOT-MERISTEMLESS, and WUSCHEL, were associated with the regeneration process. Comparison of DNA methylation profiling between leaves from young seedlings (YL) and mature plants (ML) revealed increased asymmetrical methylation in ML, which was predominantly distributed in promoter regions of genes, such as HY5 and a member of ABA-responsive element (ABRE) binding protein/ABRE binding factor, as well as genes encoding glycine-rich cell wall structural protein, CENTRORADIALIS-like protein, and beta-glucosidase 40-like essential for shoot meristem and cell wall architecture. Their opposite transcription response in ML explants during regeneration compared with those from YL demonstrated the putative involvement of DNA methylation in regeneration. Moreover, a significant lower expression of DNA glycosylase-lyase required for DNA demethylation in ML was coincident with its postponed regeneration compared with those in YL. Taken together, our results suggest a role of promoter demethylation in B. hygrometrica regeneration.

Acclimation-induced metabolic reprogramming contributes to rapid desiccation tolerance acquisition in Boea hygrometrica

The acquisition of rapid desiccation tolerance for the resurrection plant Boea hygrometrica requires a cycle of drought acclimation. Here, a gas chromatography-mass spectrometry based global untargeted metabolite profiling analysis was conducted on leaves of B. hygrometrica during dehydration and rehydration. Metabolic profiles between non-acclimated and drought acclimated plants were clearly distinguished in principal-component and hierarchical cluster analysis, indicating that drought acclimation response required the process in metabolic reprogramming. Accumulation of numerous metabolites involved in carbon and energy metabolism as well as amino acid and fatty acid biosynthesis was observed to be significantly changed upon drought acclimation and dehydration treatments. Using partial least-squares discriminant analysis, 25 known metabolites and 51 compounds with unknown structures were identified as putative biomarkers contributed to the discrimination between drought acclimated and non-acclimated plants. Remarkably, as revealed by transcriptome data analysis, some up-accumulated metabolites in acclimated plants, such as maltose, glutaric acid, L-tryptophan and α-tocopherol, which are in good correlation with the increased desiccation tolerance, and were precisely controlled by the transcript changes in multigene family members of related enzymes. Furthermore, genes positively correlated with the up-accumulated biomarkers in transcription abundances were enriched in multiple biological processes, such as “ubiquitin-dependent protein catabolism” and “abscisic acid-activated signaling pathway”. Taken together, our observations indicate that the accumulation of important metabolites correlates with the transcriptional activity of biosynthetic related enzymes and putative regulators involved in ubiquitination and ABA signal transduction during a short period of drought acclimation might contribute to the acquisition of rapid desiccation tolerance in B. hygrometrica.

Efficient modulation of photosynthetic apparatus confers desiccation tolerance in the resurrection plant Boea hygrometrica.

Boea hygrometrica (B. hygrometrica) can tolerate severe desiccation and resume photosynthetic activity rapidly upon water availability. However, little is known about the mechanisms by which B. hygrometrica adapts to dehydration and resumes competence upon rehydration. Here we determine how B. hygrometrica deals with oxidative stress, excessive excitation/electron pressures as well as photosynthetic apparatus modulation during dehydration/rehydration. By measuring ROS generation and scavenging efficiency, we found that B. hygrometrica possesses efficient strategies to maintain cellular redox homeostasis. Transmission electron microscopy (TEM) analysis revealed a remarkable alteration of chloroplast architecture and plastoglobules (PGs) accumulation during dehydration/rehydration. Pulse-amplitude modulated (PAM) chlorophyll fluorescence measurements, P700 redox assay as well as chlorophyll fluorescence emission spectra analysis on leaves of B. hygrometrica during dehydration/rehydration were also performed. Results showed that the photochemical activity of PSII as well as photoprotective energy dissipation in PSII undergo gradual inactivation/activation during dehydration/rehydration in B. hygrometrica; PSI activity is relatively induced upon water deficit, and dehydration leads to physical interaction between PSI and LHCII. Furthermore, blue-native polyacrylamide gel electrophoresis (BN-PAGE) and immunoblot analysis revealed that the protein abundance of light harvesting complexes decrease markedly along with internal water deficit to restrict light absorption and attenuate electron transfer, resulting in limited light excitation and repressed photosynthesis. In contrast, many thylakoid proteins remain at a basal level even after full dehydration. Taken together, our study demonstrated that efficient modulation of cellular redox homeostasis and photosynthetic activity confers desiccation tolerance in B. hygrometrica.

BhbZIP60 from Resurrection Plant Boea hygrometrica Is an mRNA Splicing-Activated Endoplasmic Reticulum Stress Regulator Involved in Drought Tolerance.

Adverse environmental conditions cause endoplasmic reticulum (ER) stress in plants. To mitigate ER stress damage, ER associated transcription factors and inositol-requiring enzyme-1 (IRE1)-mediated bZIP60 mRNA splicing are activated in plants. A drought-induced gene, encoding the ortholog of AtbZIP60, was identified in the resurrection plant Boea hygrometrica, termed BhbZIP60. In response to ER stress and dehydration, BhbZIP60 mRNA can be spliced to create a frame shift in the C terminus by the excision of 23b segment in a manner of its ortholog in other plants, thus translocating to the nucleus instead of the cytoplasm. The splicing-activated BhbZIP60 (BhbZIP60S) could function in the same way as its Arabidopsis ortholog by restoring the molecular phenotype of the mutant atbzip60. When overexpressed in Arabidopsis, BhbZIP60S provided transgenic plants with enhanced tolerance to drought, tunicamycin and mannitol stresses with upregulation of the expressions of ER quality control (QC) genes (BiP2, BiP3, CNX1, and sPDI) and abscisic acid (ABA) responsive genes (RD29A, RAB18, and RD17). Furthermore, in the yeast one-hybrid system, BhbZIP60S was capable of interacting with ER stress responsive elements (ERSE and ERSE-II) that exist in the promoters of known ER-QC genes, but not binding to ABA responsive cis-elements (ABREs). Our results demonstrated that drought-induced BhbZIP60 may have a function in drought tolerance via the splicing-activated BhbZIP60S to mediate ER-QC by direct binding to the promoters of ER-QC genes. This study evidently demonstrates the involvement of ER-QC in the drought tolerance of Arabidopsis and the desiccation tolerance of the resurrection plant B. hygrometrica.

Characterization of the complete chloroplast genome sequence of Lysionotus pauciflorus (Gesneriaceae)

Lysionotus pauciflorus, an evergreen subshrub with high medicinal and ecological values, mainly distributed in subtropical montane regions of China. In this study, we reported its complete chloroplast (cp) genome from Next Generation Sequencing data. The whole genome was 153,856 bp in length, containing a pair of inverted repeat region (IRs) of 25,465 bp, a large single copy (LSC) region of 85,087 bp and a small single copy (SSC) region of 17,839. The genome contained 133 genes, including 88 protein-coding genes (80 PCG species), 37 tRNA genes (28 tRNA species) and 8 rRNA genes (4 rRNA species). Among these genes, 12 genes harbored a single intron and 3 genes harbored 2 introns. The majority of gene species occurred as a single copy and one tRNA gene occurred as three copies. The overall AT content of L. pauciflorus cp genome is 62.5%. A maximum parsimony (MP) phylogenetic analysis demonstrated a close relationship between L. pauciflorus and Boea hygrometrica.

Global Transcriptome Analysis Reveals Acclimation-Primed Processes Involved in the Acquisition of Desiccation Tolerance in Boea hygrometrica.

Boea hygrometrica resurrection plants require a period of acclimation by slow soil-drying in order to survive a subsequent period of rapid desiccation. The molecular basis of this observation was investigated by comparing gene expression profiles under different degrees of water deprivation. Transcripts were clustered according to the expression profiles in plants that were air-dried (rapid desiccation), soil-dried (gradual desiccation), rehydrated (acclimated) and air-dried after acclimation. Although phenotypically indistinguishable, it was shown by principal component analysis that the gene expression profiles in rehydrated, acclimated plants resemble those of desiccated plants more closely than those of hydrated acclimated plants. Enrichment analysis based on gene ontology was performed to deconvolute the processes that accompanied desiccation tolerance. Transcripts associated with autophagy and α-tocopherol accumulation were found to be activated in both air-dried, acclimated plants and soil-dried non-acclimated plants. Furthermore, transcripts associated with biosynthesis of ascorbic acid, cell wall catabolism, chaperone-assisted protein folding, respiration and macromolecule catabolism were activated and maintained during soil-drying and rehydration. Based on these findings, we hypothesize that activation of these processes leads to the establishment of an optimal physiological and cellular state that enables tolerance during rapid air-drying. Our study provides a novel insight into the transcriptional regulation of critical priming responses to enable survival following rapid dehydration in B. hygrometrica.

The resurrection genome of Boea hygrometrica: A blueprint for survival of dehydration

"Drying without dying" is an essential trait in land plant evolution. Unraveling how a unique group of angiosperms, the Resurrection Plants, survive desiccation of their leaves and roots has been hampered by the lack of a foundational genome perspective. Here we report the ∼1,691-Mb sequenced genome of Boea hygrometrica, an important resurrection plant model. The sequence revealed evidence for two historical genome-wide duplication events, a compliment of 49,374 protein-coding genes, 29.15% of which are unique (orphan) to Boea and 20% of which (9,888) significantly respond to desiccation at the transcript level. Expansion of early light-inducible protein (ELIP) and 5S rRNA genes highlights the importance of the protection of the photosynthetic apparatus during drying and the rapid resumption of protein synthesis in the resurrection capability of Boea. Transcriptome analysis reveals extensive alternative splicing of transcripts and a focus on cellular protection strategies. The lack of desiccation tolerance-specific genome organizational features suggests the resurrection phenotype evolved mainly by an alteration in the control of dehydration response genes.

Cloning, Expression and Functional Analysis of a J-domain Protein-coding Gene, BhDNAJC2 , from the Resurrection Plant Boea hygrometrica

Cloning, Expression and Functional Analysis of a J-domain Protein-coding Gene, <i>BhDNAJC2</i> , from the Resurrection Plant <i>Boea hygrometrica</i>