Crassulacean Research Articles

Impact of green roof plant species on domestic wastewater treatment

Green roof is one of the nature-based solutions to provide environmental and social benefits for sustainable urban development. Green roofs irrigated with domestic wastewater solves not only their irrigation water resource but also the urban wastewater treatment. However, it is unknown whether the capacity of green roofs in pollutant removal meets the requirement of domestic wastewater treatment. This study was to investigate the capacity of pollutant removal by the green roofs with C4, C3, and CAM plant species when irrigated with domestic wastewater. Results showed that green roofs removed 79.27~97.38% of total suspended solids, 79.94~98.92% of chemical oxygen demand, 65.26~90.52% of total nitrogen, 83.32~96.31% of ammonium nitrogen, 77.83~93.97% of nitrate nitrogen, and 93.77~98.94% of total phosphorus, respectively. C4 and C3 plants contributed significantly higher runoff reduction, removal of total nitrogen, chemical oxygen demand, total nitrogen, ammonium nitrogen, nitrate nitrogen, phosphates, and total phosphorus than CAM plants. Water quality indicated by chemical oxygen demand, total nitrogen, ammonium nitrogen, and total phosphorus from the effluent complied with the widely accepted limits on domestic wastewater discharge. Our results demonstrate that green roofs can be designed for the ecological treatment of domestic wastewater on the household scale.

Salinity Stress Affects Photosynthesis, Malondialdehyde Formation, and Proline Content in Portulaca oleracea L.

In this investigation, the effect of salt stress on Portulaca oleracea L. was monitored at salinity levels of 100 and 300 mM NaCl. At a concentration of 100 mM NaCl there was a decrease in stomatal conductance (gs) simultaneously with an increase in CO2 assimilation (A) at the beginning of salt exposure (day 3). However, the leaf water potential (ψw), the substomatal concentration of CO2 (Ci), the maximum quantum yield of photosystem II (Fv/Fm), and the proline and malondialdehyde (MDA) content remained unchanged. Exposure to 300 mM NaCl caused a decrease in gs from day 3 and a decrease in water potential, CO2 assimilation, and Fv/Fm from day 9. There was a large increase in proline content and a significantly higher MDA concentration on days 6 and 9 of salt stress compared to the control group. After 22 days of exposure to 300 mM NaCl, there was a transition from the C4 cycle to crassulacean acid metabolism (CAM), manifested by a rapid increase in substomatal CO2 concentration and negative CO2 assimilation values. These results document the tolerance of P. oleracea to a lower level of salt stress and the possibility of its use in saline localities.

Transplanting experiment and transcriptome sequencing reveal the potential ecological adaptation to plateau environments in the allopolyploid Isoetes sinensis

Relatively high frequencies of polyploidy are generally found in high-altitude regions. However, more diploid than polyploid species of Isoetes are distributed in plateau environments in China. The low-altitude species Isoetes sinensis originates from the allopolyploidization between a plateau parent and another low altitude species. To study potential ecological adaptation to plateau environments in the allopolyploid I. sinensis, we transplanted individuals of I. sinensis to different altitudes. RNA sequencing was performed to elucidate the molecular response of this species’ ecological adaptation to plateaus. More unique differentially expressed genes (DEGs) were detected in individuals transplanted to the Qinghai–Tibet Plateau (QTP) than elsewhere, such as genes for ribosomal proteins (RPs) and succinate dehydrogenase (SDH), which helped them adapt to higher altitudes under both terrestrial and submerged conditions. In both terrestrial and submerged conditions, the expression of a large number of genes changed to help plants adapt to exposure to the high levels of ultraviolet (UV) radiation on plateaus, such as the genes associated with the accumulation of flavonoids, decreasing chlorophyll content, and reducing light harvesting activity. The expression of vacuolar-type H+-transporting ATPase (V-ATPase) and phosphoenolpyruvate carboxylase (PEPC) increased with altitude, revealing that the intensity of the crassulacean acid metabolism (CAM) of I. sinensis might be positively associated with altitude. In general, our results reveal that although I. sinensis only lives at low altitudes, it can still adapt to plateau stress by regulating the expression of certain key genes. The potential ecological adaptation to plateau environments in the allopolyploid I. sinensis may have been inherited from the plateau parent.

Engineering of Crassulacean Acid Metabolism.

Crassulacean acid metabolism (CAM) has evolved from a C3 ground state to increase water use efficiency of photosynthesis. During CAM evolution, selective pressures altered the abundance and expression patterns of C3 genes and their regulators to enable the trait. The circadian pattern of CO2 fixation and the stomatal opening pattern observed in CAM can be explained largely with a regulatory architecture already present in C3 plants. The metabolic CAM cycle relies on enzymes and transporters that exist in C3 plants and requires tight regulatory control to avoid futile cycles between carboxylation and decarboxylation. Ecological observations and modeling point to mesophyll conductance as a major factor during CAM evolution. The present state of knowledge enables suggestions for genes for a minimal CAM cycle for proof-of-concept engineering, assuming altered regulation of starch synthesis and degradation are not critical elements of CAM photosynthesis and sufficient malic acid export from the vacuole is possible.

Identification and expression profiling of genes involved in circadian clock regulation in red dragon fruit (Hylocereus polyrhizus) by full-length transcriptome sequencing

ABSTRACT Crassulacean acid metabolism (CAM) plants fix CO2 at night, exhibiting a reversed regulatory pattern of metabolomic pathways compared with most model plants, which have C3 and C4 pathways. In this study, we used a valuable tropic fruit, red dragon fruit (Hylocereus polyrhizus), as model plant to identify and analyze the circadian regulation genes. Due to the absence of red dragon fruit’s whole-genome dataset, we established a full-length transcriptome dataset using single-molecule real-time (SMRT) sequencing method. A 7.66-Gb dataset with 4,552,474 subreads was generated, with an average length of 1,683 bp and an N50 of 2,446 bp. Using this dataset, we identified center oscillator genes: CCA1 (CIRCADIAN CLOCK ASSOCIATED1), ELF3 (EARLY FLOWERING 3), GI (GIGANTEA), LHY (LATE ELONGATED HYPOCOTYL), LNK1 (NIGHT LIGHT-INDUCIBLE AND CLOCK-REGULATED 1), and TOC1 (TIMING OF CAB EXPRESSION 1); a gene for the input pathway: CRY1 (CRYPTOCHROME); a gene for the output pathway: CO (CONSTANS); and genes related to the CAM pathway: MDH (MALATE DEHYDROGENASE), ME (MALIC ENZYMES), and PPDK (PYRUVATE PHOSPHATE DIKINASE). We further established the 24-h rhythmic expression pattern of these genes and classified these into three groups: HpCCA1, HpELF3, HpLHY, HpLNK1, and HpGI have expression peaks during the day; HpTOC1, HpCO, and HpCRY1 have highest expression levels at night; The genes involved in the CAM pathways, namely, HpMDH, HpME1, and HpPPDK, have double expression peaks in the day and night. Comparison of these expression patterns between red dragon fruit and model plants could provide clues in understanding the circadian clock regulation and the activity of the CAM pathways in cactus plants.

Identification and characterization of HD-Zip genes reveals their roles in stresses responses and facultative crassulacean acid metabolism in Dendrobium catenatum

Dendrobium catenatum possesses special survival strategy including facultative crassulacean acid metabolism (CAM) to cope with various environmental stresses. The homeodomain-leucine zipper (HD-Zip) proteins had been reported to play essential roles in adaption to the environment. However, the role of the HD-Zip gene family in stresses responses and drought-induced facultative CAM in D. catenatum was largely unknown. In this study, 35 HD-Zip genes were identified in D. catenatum (DcHDZs), and were phylogenetically grouped into four subfamilies, which was further supported by the analysis of their conserved motifs and structures. Expression profile analysis of DcHD-Zip genes based on public transcriptomic data and qRT-PCR showed that most DcHD-Zip genes showed biased expression in leaf and flower than in stem and root. Three DcHD-Zip genes denominated as DcHDZ04, DcHDZ20 and DcHDZ22 belong to HD-Zip I and II subfamilies, were induced significantly under high light, low light, salt and heat stresses. Moreover, we found that the plant hormone biosynthesis and signal transduction played a vital role in facultative CAM of D. catenatum under drought, especially ABA. Nine DcHD-Zip genes were identified as DEGs and showed close relationship with several genes involved in plant hormone biosynthesis and signal transduction, suggesting their important roles in drought-induced facultative CAM of D. catenatum. This systematic analysis provided a foundation for further functional characterization of HD-Zip genes and also revealed an important regulation mechanism of facultative CAM in D. catenatum.

Comparative ecophysiology of the leaf-succulents Augea capensis (C3) and Malephora purpureo-crocea (CAM) in the Knersvlakte, Succulent Karoo, South Africa

The generally accepted assumption that CAM is an important adaptation to the drought conditions in arid deserts is mainly based on studies in controlled environments comparing the respective photosynthetic pathways in plants of different morphology. Comparative long-term field studies on the ecophysiology of C3- and CAM succulents co-occurring in the same desert habitat are too rare to satisfactorily answer the old question whether the metabolic pathway or the succulence is more important to guarantee survival in such a harsh habitat. Thus, relevant ecophysiological parameters were repeatedly monitored on plants of the leaf succulents Augea capensis (C3) and Malephora purpureo-crocea (CAM), which commonly dominate a habitat in the Knersvlakte, Namaqualand, South Africa. Under identical conditions in the same habitat, carbon gain of the C3 species was higher than that of the CAM plant, but their WUE lower and maximum photosynthetic activity nearly the same. In M. purpureo-crocea, irrigation induced rapid whole day stomatal opening at drastically increased daytime but decreased night-time CO2-uptake, while respective responses of the C3 species were delayed. These different response dynamics were due to different rooting depth, root morphology and water acquisition strategy of the flat rooting CAM and the deep-rooting C3 species. This, however, may not explain the highly similar growth success. Anyway, the results verify that CAM provides no advantage over C3 for long-term survival in the same desert environment in morphologically similar succulents.

Phosphorolytic degradation of leaf starch via plastidic α-glucan phosphorylase leads to optimized plant growth and water use efficiency over the diel phases of Crassulacean acid metabolism.

In plants with Crassulacean acid metabolism (CAM), it has been proposed that the requirement for nocturnal provision of phosphoenolpyruvate as a substrate for CO2 uptake has resulted in a re-routing of chloroplastic starch degradation from the amylolytic route to the phosphorolytic route. To test this hypothesis, we generated and characterized four independent RNAi lines of the obligate CAM species Kalanchoë fedtschenkoi with a >10-fold reduction in transcript abundance of plastidic α-glucan phosphorylase (PHS1). The rPHS1 lines showed diminished nocturnal starch degradation, reduced dark CO2 uptake, a reduction in diel water use efficiency (WUE), and an overall reduction in growth. A re-routing of starch degradation via the hydrolytic/amylolytic pathway was indicated by hyperaccumulation of maltose in all rPHS1 lines. Further examination indicated that whilst operation of the core circadian clock was not compromised, plasticity in modulating net dark CO2 uptake in response to changing photoperiods was curtailed. The data show that phosphorolytic starch degradation is critical for efficient operation of the CAM cycle and for optimizing WUE. This finding has clear relevance for ongoing efforts to engineer CAM into non-CAM species as a means of boosting crop WUE for a warmer, drier future.

Behind the scene: Critical role of reactive oxygen species and reactive nitrogen species in salt stress tolerance

AbstractSalinity is one of the most important abiotic factors which affects plant growth and development and reduces crop productivity. Plants have stress tolerance ability to respond to a particular type of stress. For salt stress alleviation, plants retain specific mechanisms, such as activation of signalling cascades, ion channels, receptors, hormonal stimulation, ion exchange, osmolytes and antioxidant enzymes which are involved either directly or indirectly in plant protection. In plants, reactive oxygen species (ROS) and reactive nitrogen species (RNS) are produced in different cell compartments and involved in the “oxidative signalling” mechanism. Based on the recent studies in signalling and mechanisms for salt tolerance in plant, we explored the role of the salt overly sensitive system (SOS) related to antiporters of plasma and mitogen‐activated protein kinase (MAPK) cascades. Considering the importance of ROS and RNS, the present review has focused on different aspects and mechanisms that play key role in plants cell signalling network in response to salinity stress. In addition, this review highlights the differential expression of ROS, RNS and various antioxidative enzymes in C3, C4 and CAM plants. Moreover, the strategies for alleviation of salt stress such as magnetopriming, nanopriming, biopriming and arbuscular mycorrhizal fungi (AMF) in plants to achieve improved salt tolerance in crops under field conditions and their effects through ROS and RNS is also discussed. We conclude the review with a discussion of unseen issues and suggestions for future researches.

The eco-evolutionary significance of rainfall constancy for facultative CAM photosynthesis.

A flexible use of the crassulacean acid metabolism (CAM) has been hypothesised to represent an intermediate stage along a C3 to full CAM evolutionary continuum, when relative contributions of C3 vs CAM metabolism are co-determined by evolutionary history and prevailing environmental constraints. However, evidence for such eco-evolutionary interdependencies is lacking. We studied these interdependencies for the leaf-succulent genus Drosanthemum (Aizoaceae, Southern African Succulent Karoo) by testing for relationships between leaf δ13 C diagnostic for CAM dependence (i.e. contribution of C3 and CAM to net carbon gain), and climatic variables related to temperature and precipitation and their temporal variation. We further quantified the effects of shared phylogenetic ancestry on CAM dependence and its relation to climate. CAM dependence is predicted by rainfall and its temporal variation, with high predictive power of rainfall constancy (temporal entropy). The predictive power of rainfall seasonality and temperature-related variables was negligible. Evolutionary history of the tested clades significantly affected the relationship between rainfall constancy and CAM dependence. We argue that higher CAM dependence might provide an adaptive advantage in increasingly unpredictable rainfall environments when the anatomic exaptation (succulence) is already present. These observations might shed light on the evolution of full CAM.

Genotypic differences relative photochemical activity, inorganic and organic solutes and yield performance in clones of the forage cactus under semi-arid environment

Plants with the crassulacean acid metabolism commonly present good adaptation to arid and semi-arid environments, but it highly depends on the type of species. In this study, chlorophyll fluorescence, the concentration of inorganic and organic solutes and the productive performance were evaluated along with their relationships in different clones of the genera Opuntia and Nopalea. The experiment was conducted from 2016 to 2018. Four clones of genus Opuntia were evaluated: ‘Orelha de Elefante Mexicana’ (OEM), ‘Orelha de Elefante Africana’ (OEA), V19 and F8; and two clones of genus Nopalea: ‘IPA Sertânia’ and ‘Miúda’. The experiment was arranged in a randomised block design, with six treatments and three replications. The following parameters were measured when harvesting: initial, maximum and variable fluorescence; the quantum yield of PSII (Fv/Fm); light-induction curves of the photochemical parameters (ΔF/Fm’, qP, NPQ and ETR); the chlorophyll and carotenoid content; carbohydrates; the sodium (Na+) and potassium (K+) content; morphometry; and dry matter accumulation. The values for the effective quantum yield of PSII (ΔF/Fm’) and the alterations in photochemical quenching were higher in the OEM clone (P < 0.05). There was a difference between clones for non-photochemical quenching, with the F8 clone having the highest values. The Fv/Fm was 0.87 for the OEM. ‘IPA Sertânia’ obtained the greatest Chl a/b, and the highest values for carbohydrate concentration were found in the OEA clone. The OEM clone showed the greatest accumulation of K+, in addition to a higher cladode area index and greater dry matter accumulation. The results of this study show the high physiological tolerance of the forage cactus to a semi-arid environment, which varies according to the clone.

Overexpression of an Agave Phosphoenolpyruvate Carboxylase Improves Plant Growth and Stress Tolerance.

It has been challenging to simultaneously improve photosynthesis and stress tolerance in plants. Crassulacean acid metabolism (CAM) is a CO2-concentrating mechanism that facilitates plant adaptation to water-limited environments. We hypothesized that the ectopic expression of a CAM-specific phosphoenolpyruvate carboxylase (PEPC), an enzyme that catalyzes primary CO2 fixation in CAM plants, would enhance both photosynthesis and abiotic stress tolerance. To test this hypothesis, we engineered a CAM-specific PEPC gene (named AaPEPC1) from Agave americana into tobacco. In comparison with wild-type and empty vector controls, transgenic tobacco plants constitutively expressing AaPEPC1 showed a higher photosynthetic rate and biomass production under normal conditions, along with significant carbon metabolism changes in malate accumulation, the carbon isotope ratio δ13C, and the expression of multiple orthologs of CAM-related genes. Furthermore, AaPEPC1 overexpression enhanced proline biosynthesis, and improved salt and drought tolerance in the transgenic plants. Under salt and drought stress conditions, the dry weight of transgenic tobacco plants overexpressing AaPEPC1 was increased by up to 81.8% and 37.2%, respectively, in comparison with wild-type plants. Our findings open a new door to the simultaneous improvement of photosynthesis and stress tolerance in plants.

Interaction among species, time-of-day, and soil water potential on biochemical and physiological characteristics of cladodes of Opuntia

The physiology and biochemistry of young Opuntia spp. cladodes relate with their Crassulacean acid metabolism, which extends over the day-night cycle in four phases, is species-dependent and is affected by water availability. This study aimed to assess the interaction among species, time-of-day, and the soil water potential (ΨW) on biochemical and physiological characteristics of cladodes of Opuntia species. Three-week-old cladodes were harvested at 7:00 a.m. and 3:00 p.m. from plants with or without irrigation for 30 d (−0.17 and −5.72 MPa soil ΨW), from O. albicarpa, O. ficus-indica, O. hyptiacantha, O. megacantha, and O. streptacantha. The experimental design was a factorial 5 x 2 x 2 (species, sampling time and soil ΨW). The experimental unit was one cladode per plant, and six repetitions were evaluated. Total acids, glucose, fructose, sucrose, starch, total phenolics, free amino acids, and soluble proteins concentrations were evaluated, as well as acid invertase and neutral invertase activities. The interaction among species x soil ΨW and species x time of the day was significant (P ≤ 0.05) in all variables evaluated. An exception was the species x soil ΨW on starch concentration (P = 0.1827). The biochemical and physiological characteristics of Opuntia cladodes were modified by the time of the day and soil ΨW interaction, but most of the characteristics were positively or inversely affected depending on the species, frequently displaying a descending trend following O. streptacantha, O. hyptiacantha, O. megacantha, O. albicarpa and O. ficus-indica. The total acids, glucose, fructose, starch, soluble proteins, and free amino acids concentrations revealed that domestication significantly modifies C and N metabolism in Opuntia.

Increasing aridity shapes beta diversity and the network dynamics of the belowground fungal microbiome associated with Opuntia ficus-indica

AimsThe effects of aridity on soil and water-use efficient (WUE) crop species are relatively well known. However, the understanding of its impacts on the dynamics of below-ground microorganisms associated with plant roots is less well understood. MethodsTo investigate the influence of increasing aridity on the dynamics of the fungal communities, samples from the root endosphere and rhizosphere associated with the prickly pear cactus trees (Opuntia ficus-indica) growing along the aridity gradient were collected and the internal transcribed spacer (ITS) were sequenced. The diversity and network analyses of fungal taxa were determined along with standard measurements of soil parameters. ResultsWe found that (i) the fungal community exhibited similar alpha diversity and shared a set of core taxa within the rhizosphere and endosphere, but there was significant beta diversity differences; (ii) the relative abundance of major phyla was higher in the rhizosphere than in the endosphere; (iii) arbuscular endomycorrhizal colonization was highest in the humid climate and decreased under lower-arid, and was negatively correlated with increased concentration of Ca2+ in the soil; (iv) increased aridity correlated with increased connectivity of the soil microbial-root fungal networks in the arid soils, producing a highly cohesive network in the upper-arid area; and (v) distinct fungal hubs sculpt the fungal microbiome network structure in the rhizosphere and endosphere within each bioclimatic zone. ConclusionsOur findings highlight the importance of gradient analysis-based correlation network as a powerful approach to understand changes in the diversity, the dynamics, and the structure of fungal communities associated with the rhizosphere-endosphere interaction and led to the identification of microbes at each bioclimatic zone that are potentially involved in promoting the survival, protection, and growth of Opuntia trees. The variability of fungal hubs composition depending on plant compartment and bioclimatic zone will give key implications for the application of rhizospheric fungi and endophytes as microbial inoculants in agriculture, as well as in the conservation and restoration of cacti plants in arid and semi-arid lands against the backdrop of climate change. Overall, this study will enhance our understanding of the microbiomes'dynamic of CAM plants in nature.

PacBio full length transcript sequencing and Illumina transcriptome insight into immune defense mechanism of Litopenaeus vannamei under ammonia-N stress

To investigate the immune defense mechanism of Litopenaeus vannamei (L. vannamei) exposed to high concentration of environmental ammonia-N, PacBio full-length transcriptome and Illumina transcriptome sequencing were performed. After ammonia-N exposure, 24,763 and 32,132 full-length transcripts were obtained, while 4465 and 3022 new genes were annotated at 0 and 6 h after compared to L. vannamei whole genome, respectively. Besides, haemocytes transcriptomes, performed at 0, 6 and 48 h, obtained a total of 1017 differentially expressed genes (DEGs), and among them 160 DEGs related to neuroendocrine-immune (NEI) were screened, of which 40 DEGs have alternative splicing form. The following experiments showed that plasma 5-HT and ACh concentrations increased significantly, and then returned to the initial level at 48 h. Moreover, cell membrane receptors (5-HT7R, ACh7R and Toll3), G-protein effectors (AC2 and PLC) and CaM all significantly upregulated, and nuclear transcription factor NF-кB was significantly downregulated, suggesting that 5-HT can act on AC-PKA, PLC - PKC and PLC - CaM pathways through 5-HT7R, and subsequently function on NF-кB together with ACh through ACh7R pathway to affects downstream effector proteins expression. Toll3 pathway is also activated to participate in signal transduction process simultaneously. Furthermore, the expressions of BGBP, PPO3, C-lectin, ALF, LYC and AIF3 were significantly increased, while Syntaxin and Cubilin were significantly decreased. The corresponding immune defense parameters including the THC, PO activity, haemocytes phagocytosis rate, antibacterial and bacteriolytic activities were significantly decreased. All results indicate that after ammonia-N stress, 5-HT, ACh and Toll3 can transfer signal into haemocytes to affect effector proteins and finally reduce immune defense parameters of L. vannamei. This study contributes to better exploration the immune defense mechanism of crustaceans under ammonia-N stress.

Five‐year field trial of the biomass productivity and water input response of cactus pear (Opuntia spp.) as a bioenergy feedstock for arid lands

AbstractClimate‐resilient and highly water‐use efficient crops are needed to meet the future food, feed, fiber, and fuel demands of a growing human population. Cactus pear (Opuntia spp.) are highly productive yet have crop water demands that are approximately 20% that of traditional crops due to their ability to perform crassulacean acid metabolism (CAM). In the first long‐term field trial of Opuntia for bioenergy in the United States, the aboveground biomass (cladode and fruit) productivity and response to different water inputs of O. cochenillifera, O. ficus‐indica, and O. streptacantha were evaluated at a planting density of 1418 plants ha−1 under three irrigation levels over a 5‐year period to investigate their response to different water inputs. Mean cladode fresh weight, cladode dry weight, cladode count, fruit fresh weight, and fruit dry weight increased linearly by 1.26‐, 1.88‐, 1.53‐, 1.89‐, and 2.13‐fold, respectively, with increasing irrigation from 300 to 716 mm year−1. Significant differences in irrigation response appeared in years 4 and 5 as the cactus trees grew larger. However, no significant differences were observed among the three Opuntia spp. for all parameters measured. Biomass productivity increased over 5 years by 140.8‐ and 132.5‐fold for cladode fresh and dry weight, respectively. Mean annual total aboveground biomass at 300, 407, and 716 mm year−1 water input resulted in 8.25, 11.16, and 15.52 Mg dry mass ha−1 year−1, respectively, at the sparse planting density used here to separate irrigation blocks, which could have been easily quadrupled. O. ficus‐indica performed better than O. cochenillifera and O. streptacantha in terms of cladode biomass and fruit count and quality. Biomass productivity was consistent with previous studies for Opuntia spp. demonstrating that cactus pear displays very high biomass and food/forage potential using substantially lower rates of supplemental irrigation than conventional crops grown in semi‐arid and arid regions.

The genome sequence of Aloe vera reveals adaptive evolution of drought tolerance mechanisms

SummaryAloe vera is a species from Asphodelaceae family having characteristics like drought resistance and numerous medicinal properties. However, the genetic basis of these phenotypes is yet unknown primarily due to unavailability of its genome sequence. Thus, we report the first Aloe vera genome sequence comprising of 12.93 Gbp and harboring 86,177 protein-coding genes. It is the first genome from Asphodelaceae family and the largest angiosperm genome sequenced and assembled till date. We also report the first genome-wide phylogeny of monocots including Aloe vera to resolve its phylogenetic position. The comprehensive comparative analysis of Aloe vera with other available high-quality monocot genomes revealed adaptive evolution in several genes of drought stress response, CAM pathway, and circadian rhythm and positive selection in DNA damage response genes in Aloe vera. This study provides clues on the genetic basis of evolution of drought stress tolerance capabilities of Aloe vera.

Ecohydrology of epiphytes: Modelling water balance, CAM photosynthesis, and their climate impacts

AbstractEpiphytes are aerial plants, often characterized by CAM (crassulacean acid metabolism) photosynthesis, which make up a significant portion of the biomass in some rainforests. Their unique characteristics have not yet been included in ecohydrological models, and their potential impact on local hydrometeorology is largely unexplored. This work introduces a water balance model for epiphytes, which adapts the soil‐plant‐atmosphere continuum model to represent a plant system without soil and couples it to the Photo3 photosynthesis model, which includes CAM photosynthesis. The model, which is parameterized with field data of Guzmania monostachia, accurately captures the observed hydraulic and photosynthetic behaviour of the epiphytic species. The application of vertical profiles of environmental inputs within the rainforest canopy shows increasing transpiration rates and decreasing water use efficiency with increasing canopy height, which corresponds to observed distributions of epiphytes in rainforests. Given that vascular epiphytes constitute a maximum of 35–50% of the foliar biomass in rainforests and contribute up to 13% of forest net primary production, they may contribute up to 10–50% of total rainforest evapotranspiration, a significant portion of the water cycle on the local ecosystem scale. The results of this work provide a missing piece to current ecohydrological models and can be integrated into Earth system models to help improve the physical representation of transpiration and free‐surface evaporation from canopy in current and future climates.

Improved method for isolation of high-quality total RNA from Agave tequilana Weber roots.

Together with their undeniable role in the ecology of arid and semiarid ecosystems, Agave species are emerging as a model to dissect the relationships between crassulacean acid metabolism and high efficiency of light and water use, and as an energy crop for bioethanol production. Transcriptome resources from economically valuable Agaves species, such as Agave tequilana and A. salmiana, as well as hybrids for fibers, are now available, and multiple gene expression landscape analyses have been reported. Key components in molecular mechanisms underlying drought tolerance could be uncovered by analyzing gene expression patterns of roots. This study describes an efficient protocol for high-quality total RNA isolation from phenolic compounds-rich Agave roots. Our methodology involves suitable root handling and collecting in the field and using saving-time commercial kits available. RNA isolated from roots free of lignified out-layers and clean cortex showed high values of quality and integrity according to electrophoresis and microfluidics-based platform. Synthesis of long full-length cDNAs and PCR amplification tested the suitability for downstream applications of extracted RNA. The protocol was applied successfully to A. tequilana roots but can be used for other Agave species that also develop lignified epidermis/exodermis in roots.

Metabolic Modeling of the C3-CAM Continuum Revealed the Establishment of a Starch/Sugar-Malate Cycle in CAM Evolution.

The evolution of Crassulacean acid metabolism (CAM) is thought to be along a C3-CAM continuum including multiple variations of CAM such as CAM cycling and CAM idling. Here, we applied large-scale constraint-based modeling to investigate the metabolism and energetics of plants operating in C3, CAM, CAM cycling, and CAM idling. Our modeling results suggested that CAM cycling and CAM idling could be potential evolutionary intermediates in CAM evolution by establishing a starch/sugar-malate cycle. Our model analysis showed that by varying CO2 exchange during the light period, as a proxy of stomatal conductance, there exists a C3-CAM continuum with gradual metabolic changes, supporting the notion that evolution of CAM from C3 could occur solely through incremental changes in metabolic fluxes. Along the C3-CAM continuum, our model predicted changes in metabolic fluxes not only through the starch/sugar-malate cycle that is involved in CAM photosynthetic CO2 fixation but also other metabolic processes including the mitochondrial electron transport chain and the tricarboxylate acid cycle at night. These predictions could guide engineering efforts in introducing CAM into C3 crops for improved water use efficiency.