Gesneriads, a Source of Resurrection and Double-Tolerant Species: Proposal of New Desiccation- and Freezing-Tolerant Plants and Their Physiological Adaptations

Decoding the physicochemical basis of resurrection: the journey of lichen Flavoparmelia caperata through prolonged water scarcity to full rehydration

Desiccation tolerance is a complex phenomenon observed in the lichen Flavoparmelia ceparata. To understand the reactivation process of desiccated thalli, completely dried samples were rehydrated. The rehydration process of this lichen occurs in two phases. The first phase, characterized by rapid rehydration, involves the conversion of non-functional reaction centers (RCs) into functional PSII RCs, and the accumulation of ROS along with the increment in SOD antioxidant enzyme. These coordinated mechanisms initiate the light reaction of photosynthesis by forming active light-harvesting complexes (LHCs). This adaptation ensures efficient recovery, as evidenced by specific energy fluxes (ABS/RC, TR/RC, ET/RC, and DI/RC), phenomenological fluxes (ABS/CS, TR/CS, ET/CS, and DI/CS), quantum efficiencies (ФP0, ФE0, and ФD0), primary and secondary photochemistry, photochemical and non-photochemical quenching, and performance index, highlighting the essential role of rapid water uptake in restoring turgor pressure for cell structure and function maintenance. The interconnected network of antioxidant defenses, including catalase (CAT) and peroxidase (POD), underscores the plant's ability to cope with oxidative stress during resilience. The acid phosphomonoesterase (PME) enzymatic activity corresponds to its role in releasing phosphate for essential cellular functions and post-rehydration thallus growth. The activity of CAT, GPOD, and PME signifies the gradual reactivation of lichen F. caperata. Moreover, the investigation into chlorophyll a fluorescence emphasizes the efficient reactivation of the photosynthetic process in F. caperata. In conclusion, lichen F. caperata demonstrates significant potential for desiccation tolerance through the rapid transformation of chloroplasts, chlorophylls, and PSII RCs from their inactive to active states upon rehydration. This research not only enhances our understanding of desiccation tolerance in resurrection plants but also highlights the importance of lichens, particularly F. caperata, as valuable models for studying plant resilience in challenging environments.

Resurrection Plants-A Valuable Source of Natural Bioactive Compounds: From Word-of-Mouth to Scientifically Proven Sustainable Use

Resurrection plant species are a group of higher plants whose vegetative tissues are able to withstand long periods of almost full desiccation and recover quickly upon rewatering. Apart from being a model system for studying desiccation tolerance, resurrection plant species appear to be a valuable source of metabolites, with various areas of application. A significant number of papers have been published in recent years with respect to the extraction and application of bioactive compounds from higher resurrection plant species in various test systems. Promising results have been obtained with respect to antioxidative and antiaging effects in various test systems, particularly regarding valuable anticancer effects in human cell lines. Here, we review the latest advances in the field and propose potential mechanisms of action of myconoside-a predominant secondary compound in the European members of the Gesneriaceae family. In addition, we shed light on the possibilities for the sustainable use of natural products derived from resurrection plants.

Dynamics of chromatin accessibility and genome wide control of desiccation tolerance in the resurrection plant Haberlea rhodopensis

BACKGROUND

Drought is one of the main consequences of global climate change and this problem is expected to intensify in the future. Resurrection plants evolved the ability to withstand the negative impact of long periods of almost complete desiccation and to recover at rewatering. In this respect, many physiological, transcriptomic, proteomic and genomic investigations have been performed in recent years, however, few epigenetic control studies have been performed on these valuable desiccation-tolerant plants so far.

RESULTS

In the present study, for the first time for resurrection plants we provide evidences about the differential chromatin accessibility of Haberlea rhodopensis during desiccation stress by ATAC-seq (Assay for Transposase Accessible Chromatin with high-throughput sequencing). Based on gene similarity between species, we used the available genome of the closely related resurrection plant Dorcoceras hygrometricum to identify approximately nine hundred transposase hypersensitive sites (THSs) in H. rhodopensis. The majority of them corresponds to proximal and distal regulatory elements of different genes involved in photosynthesis, carbon metabolism, synthesis of secondary metabolites, cell signalling and transcriptional regulation, cell growth, cell wall, stomata conditioning, chaperons, oxidative stress, autophagy and others. Various types of binding motifs recognized by several families of transcription factors have been enriched from the THSs found in different stages of drought. Further, we used the previously published RNA-seq data from H. rhodopensis to evaluate the expression of transcription factors putatively interacting with the enriched motifs, and the potential correlation between the identified THS and the expression of their corresponding genes.

CONCLUSIONS

These results provide a blueprint for investigating the epigenetic regulation of desiccation tolerance in resurrection plant H. rhodopensis and comparative genomics between resurrection and non-resurrection species with available genome information.

The Inhibitory Effects and Cytotoxic Activities of the Stem Extract of Nepenthes miranda against Single-Stranded DNA-Binding Protein and Oral Carcinoma Cells

The carnivorous pitcher plants of the genus Nepenthes exhibit many ethnobotanical uses, including treatments of stomachache and fever. In this study, we prepared different extracts from the pitcher, stem, and leaf extracts of Nepenthes miranda obtained using 100% methanol and analyzed their inhibitory effects on recombinant single-stranded DNA-binding protein (SSB) from Klebsiella pneumoniae (KpSSB). SSB is essential for DNA replication and cell survival and thus an attractive target for potential antipathogen chemotherapy. Different extracts prepared from Sinningia bullata, a tuberous member of the flowering plant family Gesneriaceae, were also used to investigate anti-KpSSB properties. Among these extracts, the stem extract of N. miranda exhibited the highest anti-KpSSB activity with an IC₅₀ value of 15.0 ± 1.8 μg/mL. The cytotoxic effects of the stem extract of N. miranda on the survival and apoptosis of the cancer cell lines Ca9-22 gingival carcinoma, CAL27 oral adenosquamous carcinoma, PC-9 pulmonary adenocarcinoma, B16F10 melanoma, and 4T1 mammary carcinoma cells were also demonstrated and compared. Based on collective data, the cytotoxic activities of the stem extract at a concentration of 20 μg/mL followed the order Ca9-22 > CAL27 > PC9 > 4T1 > B16F10 cells. The stem extract of N. miranda at a concentration of 40 μg/mL completely inhibited Ca9-22 cell migration and proliferation. In addition, incubation with this extract at a concentration of 20 μg/mL boosted the distribution of the G2 phase from 7.9% to 29.2% in the Ca9-22 cells; in other words, the stem extract might suppress Ca9-22 cell proliferation by inducing G2 cell cycle arrest. Through gas chromatography-mass spectrometry, the 16 most abundant compounds in the stem extract of N. miranda were tentatively identified. The 10 most abundant compounds in the stem extract of N. miranda were used for docking analysis, and their docking scores were compared. The binding capacity of these compounds was in the order sitosterol > hexadecanoic acid > oleic acid > plumbagin > 2-ethyl-3-methylnaphtho[2,3-b]thiophene-4,9-dione > methyl α-d-galactopyranoside > 3-methoxycatechol > catechol > pyrogallol > hydroxyhydroquinone; thus, sitosterol might exhibit the greatest inhibitory capacity against KpSSB among the selected compounds. Overall, these results may indicate the pharmacological potential of N. miranda for further therapeutic applications.

Acquisition of Freezing Tolerance of Resurrection Species from Gesneriaceae, a Comparative Study

Resurrection plants have the unique ability to restore normal physiological activity after desiccation to an air-dry state. In addition to their desiccation tolerance, some of them, such as Haberlea rhodopensis and Ramonda myconi, are also freezing-tolerant species, as they survive subzero temperatures during winter. Here, we compared the response of the photosynthetic apparatus of two other Gesneriaceae species, Ramonda serbica and Ramonda nathaliae, together with H. rhodopensis, to cold and freezing temperatures. The role of some protective proteins in freezing tolerance was also investigated. The water content of leaves was not affected during cold acclimation but exposure of plants to -10 °C induced dehydration of plants. Freezing stress strongly reduced the quantum yield of PSII photochemistry (Y(II)) and stomatal conductance (g_s) on the abaxial leaf side. In addition, the decreased ratio of F_v/F_m suggested photoinhibition or sustained quenching. Freezing-induced desiccation resulted in the inhibition of PSII activity, which was accompanied by increased thermal energy dissipation. In addition, an increase of dehydrins and ELIPs was detected, but the protein pattern differed between species. During recovery, the protein abundance decreased and plants completely recovered their photosynthetic activity. Thus, our results showed that R. serbica, R. nathaliae, and H. rhodopensis survive freezing stress due to some resurrection-linked traits and confirmed their freezing tolerance.

Morphological, physiological and biochemical response of Lallemantia species to elevated temperature and light duration during seed development

Seed weight, storability, and germinability can depend on maternal plant's environment. However, there is slight information about the effect of light and temperature on seed quality of Lallemantia species. The purpose of this research was to determine the properties of physio-biochemical of maternal plant, seed quality, and seed chemical composition of Lallemantia species (Lallemantia iberica and Lallemantia royleana) under temperature (15 °C, 25 °C, and 35 °C) and photoperiod (8 hd^-1, 16 hd^-1, and 24 hd^-1) maternal plants environment. Increasing temperature and photoperiod caused a reduction in leaf chlorophyll, stomatal movement, total soluble sugar, superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) enzymes activities, and an increment in malondialdehyde (MDA) and hydrogen peroxide (H2O2) content of seeds. However, the highest weight, germination, vigor index, and longevity, seed chemical compositions were obtained in offspring which matured under 25 °C for 16 hd^-1. The highest germination, oil, and relative percentage of fatty acids (oleic acid (OA), linoleic acid (LA), and linolenic acid (LNA)) were obtained in L. iberica seeds. On the contrary, longevity, mucilage, and sucrose were more abundant in L. royleana seeds. Overall, this research has clearly shown that temperature and light quality and quantity of maternal plant's environment have an immensely effect on producing of seeds with high-quality. However, it is necessary to investigate the impact of the epigenetic mechanisms of the maternal plant on the offspring in future studies.

Cytotoxic, Antibacterial, and Antioxidant Activities of the Leaf Extract of Sinningia bullata

Sinningia bullata is a tuberous member of the flowering plant family Gesneriaceae. Prior to this work, the antibacterial, antioxidant, and cytotoxic properties of S. bullata were undetermined. Here, we prepared different extracts from the leaf, stem, and tuber of S. bullata and investigated their pharmacological activities. The leaf extract of S. bullata, obtained by 100% acetone (Sb-L-A), had the highest total flavonoid content, antioxidation capacity, and cytotoxic and antibacterial activities. Sb-L-A displayed a broad range of antibacterial activities against Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa. The inhibition zones of Sb-L-A ranged from 8 to 30 mm and were in the following order: S. aureus > E. coli > P. aeruginosa. Incubation of B16F10 melanoma cells with Sb-L-A at a concentration of 80 μg/mL caused deaths at the rate of 96%, reduced migration by 100%, suppressed proliferation and colony formation by 99%, and induced apoptosis, which was observed in 96% of the B16F10 cells. In addition, the cytotoxic activities of Sb-L-A were synergistically enhanced when coacting with the antitumor drug epothilone B. Sb-L-A was also used to determine the cytotoxic effects against 4T1 mammary carcinoma cells. Sb-L-A of 60 μg/mL boosted the distribution of the G2 phase from 1.4% to 24.4% in the B16F10 cells. Accordingly, Sb-L-A might suppress melanoma cell proliferation by inducing G2 cell-cycle arrest. The most abundant compounds in Sb-L-A were identified using gas chromatography-mass spectrometry. Overall, the collective data in this study may indicate the pharmacological potentials of Sb-L-A for possible medical applications.