Crassulacean Acid Metabolism Pathway Research Articles

Gene duplications facilitate C4-CAM compatibility in common purslane.

Common purslane (Portulaca oleracea) integrates both C4 and crassulacean acid metabolism (CAM) photosynthesis pathways and is a promising model plant to explore C4-CAM plasticity. Here, we report a high-quality chromosome-level genome of nicotinamide adenine dinucleotide (NAD)-malic enzyme (ME) subtype common purslane that provides evidence for 2 rounds of whole-genome duplication (WGD) with an ancient WGD (P-β) in the common ancestor to Portulacaceae and Cactaceae around 66.30 million years ago (Mya) and another (Po-α) specific to common purslane lineage around 7.74 Mya. A larger number of gene copies encoding key enzymes/transporters involved in C4 and CAM pathways were detected in common purslane than in related species. Phylogeny, conserved functional site, and collinearity analyses revealed that the Po-α WGD produced the phosphoenolpyruvate carboxylase-encoded gene copies used for photosynthesis in common purslane, while the P-β WGD event produced 2 ancestral genes of functionally differentiated (C4- and CAM-specific) beta carbonic anhydrases involved in the C4 + CAM pathways. Additionally, cis-element enrichment analysis in the promoters showed that CAM-specific genes have recruited both evening and midnight circadian elements as well as the Abscisic acid (ABA)-independent regulatory module mediated by ethylene-response factor cis-elements. Overall, this study provides insights into the origin and evolutionary process of C4 and CAM pathways in common purslane, as well as potential targets for engineering crops by integrating C4 or CAM metabolism.

The climate changes promoted the chloroplast genomic evolution of Dendrobium orchids among multiple photosynthetic pathways

Dendrobium orchids have multiple photosynthetic pathways, which can be used as a model system for studying the evolution of crassulacean acid metabolism (CAM). In this study, based on the results of the net photosynthetic rates (Pn), we classified Dendrobium species into three photosynthetic pathways, then employed and compared their chloroplast genomes. The Dendrobium chloroplast genomes have typical quartile structures, ranging from 150,841–153,038 bp. The apparent differences in GC content, sequence variability, and IR junctions of SSC/IRB junctions (JSBs) were measured within chloroplast genomes among different photosynthetic pathways. The phylogenetic analysis has revealed multiple independent CAM origins among the selected Dendrobium species. After counting insertions and deletions (InDels), we found that the occurrence rates and distribution densities among different photosynthetic pathways were inconsistent. Moreover, the evolution patterns of chloroplast genes in Dendrobium among three photosynthetic pathways were also diversified. Considering the diversified genome structure variations and the evolution patterns of protein-coding genes among Dendrobium species, we proposed that the evolution of the chloroplast genomes was disproportional among different photosynthetic pathways. Furthermore, climatic correlation revealed that temperature and precipitation have influenced the distribution among different photosynthetic pathways and promoted the foundation of CAM pathway in Dendrobium orchids. Based on our study, we provided not only new insights into the CAM evolution of Dendrobium but also provided beneficial genetic data resources for the further systematical study of Dendrobium.

Diel dynamics of multi-omics in elkhorn fern provide new insights into weak CAM photosynthesis

Crassulacean acid metabolism (CAM) has high water-use efficiency (WUE) and is widely recognized to have evolved from C3 photosynthesis. Different plant lineages have convergently evolved CAM, but the molecular mechanism that underlies C3-to-CAM evolution remains to be clarified. Platycerium bifurcatum (elkhorn fern) provides an opportunity to study the molecular changes underlying the transition from C3 to CAM photosynthesis because both modes of photosynthesis occur in this species, with sporotrophophyll leaves (SLs) and cover leaves (CLs) performing C3 and weak CAM photosynthesis, respectively. Here, we report that the physiological and biochemical attributes of CAM in weak CAM-performing CLs differed from those in strong CAM species. We investigated the diel dynamics of the metabolome, proteome, and transcriptome in these dimorphic leaves within the same genetic background and under identical environmental conditions. We found that multi-omic diel dynamics in P. bifurcatum exhibit both tissue and diel effects. Our analysis revealed temporal rewiring of biochemistry relevant to the energy-producing pathway (TCA cycle), CAM pathway, and stomatal movement in CLs compared with SLs. We also confirmed that PHOSPHOENOLPYRUVATE CARBOXYLASE KINASE (PPCK) exhibits convergence in gene expression among highly divergent CAM lineages. Gene regulatory network analysis identified candidate transcription factors regulating the CAM pathway and stomatal movement. Taken together, our results provide new insights into weak CAM photosynthesis and new avenues for CAM bioengineering.

Do photosynthetic metabolism and habitat influence foliar water uptake in orchids?

Epiphytic and rupicolous plants inhabit environments with limited water resources. Such plants commonly use Crassulacean Acid Metabolism (CAM), a photosynthetic pathway that accumulates organic acids in cell vacuoles at night, so reducing their leaf water potential and favouring water absorption. Foliar water uptake (FWU) aids plant survival during drought events in environments with high water deficits. We hypothesized that FWU represents a strategy employed by epiphytic and rupicolous orchids for water acquisition and that CAM will favour increased water absorption. We examined 6 epiphyte, 4 terrestrial and 6 rupicolous orchids that use C3 (n=9) or CAM (n=7) pathways. Five individuals per species were used to evaluate FWU, structural characteristics and leaf water balance. Rupicolous species with C3 metabolism had higher FWU than other species. FWU (Cmax and k) could be related to succulence, SLM and leaf RWC. The results indicated that high orchid leaf densities favoured FWU, as area available for water storage increases with leaf density. Structural characteristics linked to water storage (e.g. high RWC, succulence), on the other hand, could limit leaf water absorption by favouring high internal leaf water potentials. Epiphytic, rupicolous and terrestrial orchids showed FWU. Rupicolous species had high levels of FWU, probably through absorption from mist. However, succulence in plants with CAM appears to mitigate FWU.

High-quality ice plant reference genome analysis provides insights into genome evolution and allows exploration of genes involved in the transition from C3 to CAM pathways.

Ice plant (Mesembryanthemum crystallinum), a member of the Aizoaceae family, is a typical halophyte crop and a model plant for studying the mechanism of transition from C3 photosynthesis to crassulacean acid metabolism (CAM). Here, we report a high-quality chromosome-level ice plant genome sequence. This 98.05% genome sequence is anchored to nine chromosomes, with a total length of 377.97 Mb and an N50 scaffold of 40.45 Mb. Almost half of the genome (48.04%) is composed of repetitive sequences, and 24 234 genes have been annotated. Subsequent to the ancient whole-genome triplication (WGT) that occurred in eudicots, there has been no recent whole-genome duplication (WGD) or WGT in ice plants. However, we detected a novel WGT event that occurred in the same order in Simmondsia chinensis, which was previously overlooked. Our findings revealed that ice plants have undergone chromosome rearrangements and gene removal during evolution. Combined with transcriptome and comparative genomic data and expression verification, we identified several key genes involved in the CAM pathway and constructed a comprehensive network. As the first genome of the Aizoaceae family to be released, this report will provide a rich data resource for comparative and functional genomic studies of Aizoaceae, especially for studies on salt tolerance and C3-to-CAM transitions to improve crop yield and resistance.

A comparison in species distribution model performance of succulents using key species and subsets of environmental predictors.

Identifying the environmental drivers of the global distribution of succulent plants using the Crassulacean acid metabolism pathway of photosynthesis has previously been investigated through ensemble‐modeling of species delimiting the realized niche of the natural succulent biome. An alternative approach, which may provide further insight into the fundamental niche of succulent plants in the absence of dispersal limitation, is to model the distribution of selected species that are globally widespread and have become naturalized far beyond their native habitats. This could be of interest, for example, in defining areas that may be suitable for cultivation of alternative crops resilient to future climate change. We therefore explored the performance of climate‐only species distribution models (SDMs) in predicting the drivers and distribution of two widespread CAM plants, Opuntia ficus‐indica and Euphorbia tirucalli. Using two different algorithms and five predictor sets, we created distribution models for these exemplar species and produced an updated map of global inter‐annual rainfall predictability. No single predictor set produced markedly more accurate models, with the basic bioclim‐only predictor set marginally out‐performing combinations with additional predictors. Minimum temperature of the coldest month was the single most important variable in determining spatial distribution, but additional predictors such as precipitation and inter‐annual precipitation variability were also important in explaining the differences in spatial predictions between SDMs. When compared against previous projections, an a posteriori approach correctly does not predict distributions in areas of ecophysiological tolerance yet known absence (e.g., due to biotic competition). An updated map of inter‐annual rainfall predictability has successfully identified regions known to be depauperate in succulent plants. High model performance metrics suggest that the majority of potentially suitable regions for these species are predicted by these models with a limited number of climate predictors, and there is no benefit in expanding model complexity and increasing the potential for overfitting.

Evolution of an intermediate C4 photosynthesis in the non-foliar tissues of the Poaceae.

Carbon concentrating mechanisms (CCMs) in plants are abaptive features that have evolved to sustain plant growth in unfavorable environments, especially at low atmospheric carbon levels and high temperatures. Uptake of CO2 and its storage in the aerenchyma tissues of Lycopsids and diurnal acidity fluctuation in aquatic plants during the Palaeozoic era (ca. 300Ma.) would represent the earliest evolution of a CCM. The CCM parts of the dark reactions of photosynthesis have evolved many times, while the light reactions are conserved across plant lineages. A C4 type CCM, leaf C4 photosynthesis is evolved in the PACMAD clade of the Poaceae family. The evolution of C4 photosynthesis from C3 photosynthesis was an abaptation. Photosynthesis in reproductive tissues of sorghum and maize (PACMAD clade) has been shown to be of a weaker C4 type (high CO2 compensation point, low carbon isotope discrimination, and lack of Rubisco compartmentalization, when compared to the normal C4 types) than that in the leaves (normal C4 type). However, this does not fit well with the character polarity concept from an evolutionary perspective. In a recent model proposed for CCM evolution, the development of a rudimentary CCM prior to the evolution of a more efficient CCM (features contrasting to a weaker C4 type, leading to greater biomass production rate) has been suggested. An intermediate crassulacean acid metabolism (CAM) type of CCM (rudimentary) was reported in the genera, Brassia, Coryanthes, Eriopsis, Peristeria, of the orchids (well-known group of plants that display the CAM pathway). Similarly, we propose here the evolution of a rudimentary CCM (C4-like type pathway) in the non-foliar tissues of the Poaceae, prior to the evolution of the C4 pathway as identified in the leaves of the C4 species of the PACMAD clade.

Functional relationship between leaf/stem pseudobulb size and photosynthetic pathway in the Orchidaceae

Water storage has been commonly cited as an important function of orchid pseudobulbs, and it is reasonable to assume that orchids which utilize crassulacean acid metabolism (CAM) photosynthesis have larger pseudobulbs than those of C3 orchid taxa, because these foliar (or stem) structures may reflect another type of succulent tissue in CAM plants. On the other hand, it is equally plausible that C3 orchids have larger pseudobulbs, as they lack succulent tissue, as well as the water-conservative CAM pathway. The goal of this study was to compare pseudobulb size in over 100 living orchid species growing at the Missouri Botanical Garden by measurement. Pseudobulb volumes of C3 species did not differ from those of species with CAM photosynthesis in a family-wide comparison of all sampled species, as well as in comparisons of taxa with these two photosynthetic pathways among three subtribes and within one genus. The results did not support a functional relationship between pseudobulb volume and photosynthetic pathway in the Orchidaceae. Pseudobulbs are equally important structures in C3 and CAM orchid taxa, and may function similarly in water, carbohydrates, and (or) essential elements storage in the two groups of orchids. This study lays a foundation for further research into pseudobulb evolution in orchids.

Exploring the effects of elevated carbon dioxide mediated global warming phenomenon in photosynthesis: challenges and future directions

Photosynthesis is a plant-physiological mechanism that transforms light energy into chemical energy. It is the only mechanism for food preparation in the form of complex sugar. Rise in the concentration of greenhouse gases (GHGs) and water vapour causes a hike in global temperature known as global warming. Increasing temperature causes climate change by changing the weathering pattern. Climate change affects photosynthesis in C3, C4, and Crassulacean acid metabolism (CAM) plants. The focus of this review is to highlight the impact of elevated CO2 mediated global warming on photosynthesis. CO2 is the most abundant greenhouse gas. The elevated CO2 level in the atmosphere increases the photosynthesis rate in plants until a certain level. Increased heat caused by higher CO2 concentration disrupts the photosynthetic machineries. Moreover, the increased level of temperature built up by a higher amount of atmospheric CO2 concentration on the C3, C4, and CAM pathway follower plants are discussed thoroughly.

CAM photosynthesis: the acid test.

SummaryThere is currently considerable interest in the prospects for bioengineering crassulacean acid metabolism (CAM) photosynthesis – or key elements associated with it, such as increased water‐use efficiency – into C3 plants. Resolving how CAM photosynthesis evolved from the ancestral C3 pathway could provide valuable insights into the targets for such bioengineering efforts. It has been proposed that the ability to accumulate organic acids at night may be common among C3 plants, and that the transition to CAM might simply require enhancement of pre‐existing fluxes, without the need for changes in circadian or diurnal regulation. We show, in a survey encompassing 40 families of vascular plants, that nocturnal acidification is a feature entirely restricted to CAM species. Although many C3 species can synthesize malate during the light period, we argue that the switch to night‐time malic acid accumulation requires a fundamental metabolic reprogramming that couples glycolytic breakdown of storage carbohydrate to the process of net dark CO2 fixation. This central element of the CAM pathway, even when expressed at a low level, represents a biochemical capability not seen in C3 plants, and so is better regarded as a discrete evolutionary innovation than as part of a metabolic continuum between C3 and CAM.

Underwater CAM photosynthesis elucidated by Isoetes genome

To conserve water in arid environments, numerous plant lineages have independently evolved Crassulacean Acid Metabolism (CAM). Interestingly, Isoetes, an aquatic lycophyte, can also perform CAM as an adaptation to low CO2 availability underwater. However, little is known about the evolution of CAM in aquatic plants and the lack of genomic data has hindered comparison between aquatic and terrestrial CAM. Here, we investigate underwater CAM in Isoetes taiwanensis by generating a high-quality genome assembly and RNA-seq time course. Despite broad similarities between CAM in Isoetes and terrestrial angiosperms, we identify several key differences. Notably, Isoetes may have recruited the lesser-known ‘bacterial-type’ PEPC, along with the ‘plant-type’ exclusively used in other CAM and C4 plants for carboxylation of PEP. Furthermore, we find that circadian control of key CAM pathway genes has diverged considerably in Isoetes relative to flowering plants. This suggests the existence of more evolutionary paths to CAM than previously recognized.

Genomic insights into the fast growth of paulownias and the formation of Paulownia witches' broom

Paulownias are among the fastest growing trees in the world, but they often suffer tremendous loss of wood production due to infection by Paulownia witches' broom (PaWB) phytoplasmas. In this study, we have sequenced and assembled a high-quality nuclear genome of Paulownia fortunei, a commonly cultivated paulownia species. The assembled genome of P. fortunei is 511.6 Mb in size, with 93.2% of its sequences anchored to 20 pseudo-chromosomes, and it contains 31 985 protein-coding genes. Phylogenomic analyses show that the family Paulowniaceae is sister to a clade composed of Phrymaceae and Orobanchaceae. Higher photosynthetic efficiency is achieved by integrating C3 photosynthesis and the crassulacean acid metabolism pathway, which may contribute to the extremely fast growth habit of paulownia trees. Comparative transcriptome analyses reveal modules related to cambial growth and development, photosynthesis, and defense responses. Additional genome sequencing of PaWB phytoplasma, combined with functional analyses, indicates that the effector PaWB-SAP54 interacts directly with Paulownia PfSPLa, which in turn causes the degradation of PfSPLa by the ubiquitin-mediated pathway and leads to the formation of witches' broom. Taken together, these results provide significant insights into the biology of paulownias and the regulatory mechanism for the formation of PaWB.

Transcriptome and Degradome Profiling Reveals a Role of miR530 in the Circadian Regulation of Gene Expression in Kalanchoë marnieriana.

Crassulacean acid metabolism (CAM) is an important photosynthetic pathway for plant adaptation to dry environments. CAM plants feature a coordinated interaction between mesophyll and epidermis functions that involves refined regulations of gene expression. Plant microRNAs (miRNAs) are crucial post-transcription regulators of gene expression, however, their roles underlying the CAM pathway remain poorly investigated. Here, we present a study characterizing the expression of miRNAs in an obligate CAM species Kalanchoë marnieriana. Through sequencing of transcriptome and degradome in mesophyll and epidermal tissues under the drought treatments, we identified differentially expressed miRNAs that were potentially involved in the regulation of CAM. In total, we obtained 84 miRNA genes, and eight of them were determined to be Kalanchoë-specific miRNAs. It is widely accepted that CAM pathway is regulated by circadian clock. We showed that miR530 was substantially downregulated in epidermal peels under drought conditions; miR530 targeted two tandem zinc knuckle/PLU3 domain encoding genes (TZPs) that were potentially involved in light signaling and circadian clock pathways. Our work suggests that the miR530-TZPs module might play a role of regulating CAM-related gene expression in Kalanchoë.

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.

Studi Degreening, Kesegaran, dan Daya Simpan Buah Naga Merah (Hylocereus polyrhizus (Weber) Britton & Rose) untuk Menentukan Kriteria Panen Optimum

Buah naga merah adalah buah non klimakterik dengan lintasan fotosintesis crassulacean acid metabolism. Kematangan optimum ditandai dengan warna kulit buah merah 100%. Tujuan percobaan adalah mempelajari perubahan warna kulit terkait dengan kesegaran dan daya simpan buah naga merah untuk menentukan kriteria panen optimum. Bahan percobaan disiapkan di kebun Sabisa Farm, Sindang Barang, Bogor (60 35’ 16” LS, 1060 46’ BT; elevasi 219 m di atas permukaan laut). Percobaan menggunakan rancangan kelompok lengkap teracak dengan perlakuan 5 taraf umur panen, yaitu 30, 32, 34, 36, dan 38 hari setelah antesis (HSA) dengan 5 ulangan. Hasil percobaan menunjukkan bahwa kulit buah naga merah 30 HSA memiliki skala warna 2 (1-25% merah), buah 32 HSA memiliki skala warna 4 (26-50% merah), dan buah 34, 36, dan 38 HSA telah mencapai skala warna 6 (100% merah) ketika dipanen. Kulit buah 30 HSA memerlukan waktu 6 hari setelah panen (HSP) dan buah 32 HSA memerlukan waktu 3 HSP untuk mencapai warna merah 100%. Pada saat warna merah 100%, buah 30 - 38 HSA memiliki kandungan padatan terlarut total 11.7 hingga 13.5 oBrix yang masih memenuhi standard pemasaran buah naga sebesar 11.0 oBrix. Kandungan asam tertitrasi total menurun, tetapi kandungan vitamin C meningkat dengan meningkatnya umur panen.
 Kata kunci: CAM, kematangan pascapanen, kesegaran buah, satuan panas, tanaman hari-panjang

How to resolve the enigma of diurnal malate remobilisation from the vacuole in plants with crassulacean acid metabolism?

Opening of stomata in plants with crassulacean acid metabolism (CAM) is mainly shifted to the night period when atmospheric CO2 is fixed by phosphoenolpyruvate carboxylase and stored as malic acid in the vacuole. As such, CAM plants ameliorate transpirational water losses and display substantially higher water-use efficiency compared with C3 and C4 plants. In the past decade significant technical advances have allowed an unprecedented exploration of genomes, transcriptomes, proteomes and metabolomes of CAM plants and efforts are ongoing to engineer the CAM pathway in C3 plants. Whilst research efforts have traditionally focused on nocturnal carboxylation, less information is known regarding the drivers behind diurnal malate remobilisation from the vacuole that liberates CO2 to be fixed by RuBisCo behind closed stomata. To shed more light on this process, we provide a stoichiometric analysis to identify potentially rate-limiting steps underpinning diurnal malate mobilisation and help direct future research efforts. Within this remit we address three key questions: Q1 Does light-dependent assimilation of CO2 via RuBisCo dictate the rate of malate mobilisation? Q2: Do the enzymes responsible for malate decarboxylation limit daytime mobilisation from the vacuole? Q3: Does malate efflux from the vacuole set the pace of decarboxylation?

The Development of Crassulacean Acid Metabolism (CAM) Photosynthesis in Cotyledons of the C4 Species, Portulaca grandiflora (Portulacaceae).

Portulaca grandiflora simultaneously utilizes both the C4 and Crassulacean acid metabolism (CAM) photosynthetic pathways. Our goal was to determine whether CAM developed and was functional simultaneously with the C4 pathway in cotyledons of P. grandiflora. We studied during development whether CAM would be induced with water stress by monitoring the enzyme activity, leaf structure, JO2 (rate of O2 evolution calculated by fluorescence analysis), and the changes in titratable acidity of 10 and 25 days old cotyledons. In the 10 days old cotyledons, C4 and CAM anatomy were evident within the leaf tissue. The cotyledons showed high titratable acid levels but a small CAM induction. In the 25 days old cotyledons, there was a significant acid fluctuation under 7 days of water stress. The overall enzyme activity was reduced in the 10 days old plants, while in the 25 days old plants CAM activity increased under water-stressed conditions. In addition to CAM, the research showed the presence of glycine decarboxylase in the CAM tissue. Thus, it appears both pathways develop simultaneously in the cotyledons but the CAM pathway, due to anatomical constraints, may be slower to develop than the C4 pathway. Cotyledons showed the ancestral Atriplicoid leaf anatomy, which leads to the question: Could a CAM cell be the precursor to the C4 pathway? Further study of this may lead to understanding into the evolution of C4 photosynthesis in the Portulaca.

Biosystems Design to Accelerate C3-to-CAM Progression.

Global demand for food and bioenergy production has increased rapidly, while the area of arable land has been declining for decades due to damage caused by erosion, pollution, sea level rise, urban development, soil salinization, and water scarcity driven by global climate change. In order to overcome this conflict, there is an urgent need to adapt conventional agriculture to water-limited and hotter conditions with plant crop systems that display higher water-use efficiency (WUE). Crassulacean acid metabolism (CAM) species have substantially higher WUE than species performing C3 or C4 photosynthesis. CAM plants are derived from C3 photosynthesis ancestors. However, it is extremely unlikely that the C3 or C4 crop plants would evolve rapidly into CAM photosynthesis without human intervention. Currently, there is growing interest in improving WUE through transferring CAM into C3 crops. However, engineering a major metabolic plant pathway, like CAM, is challenging and requires a comprehensive deep understanding of the enzymatic reactions and regulatory networks in both C3 and CAM photosynthesis, as well as overcoming physiometabolic limitations such as diurnal stomatal regulation. Recent advances in CAM evolutionary genomics research, genome editing, and synthetic biology have increased the likelihood of successful acceleration of C3-to-CAM progression. Here, we first summarize the systems biology-level understanding of the molecular processes in the CAM pathway. Then, we review the principles of CAM engineering in an evolutionary context. Lastly, we discuss the technical approaches to accelerate the C3-to-CAM transition in plants using synthetic biology toolboxes.

Drought survival strategies of juvenile bromeliads of Alcantarea imperialis (Carrière) Harms

The establishment of bromeliad populations in rupicolous environments depends on the efficient survival strategy of juvenile individuals under adverse conditions, such as drought. Juvenile plants of Alcantarea imperialis do not form water reservoir (phytotelm) as adult individuals and then they require metabolic mechanisms to cope with water deficit during the initial stages of plant growth. It has been reported that sugar accumulation and crassulacean acid metabolism (CAM) photosynthesis are related to plant responses to water deficit. This study investigated whether these physiological adjustments could be dual strategies to drought survive of juvenile A. imperialis plants. Plants were cultivated in vitro with polyethylene glycol 6000 (PEG 6000) to simulate different degrees of water deficit (moderate stress, − 1.9 mega Pascal (MPa) and severe stress, − 8.5 MPa) and a control treatment without PEG (− 0.5 MPa) for 7, 15 and 30 days. Plant growth, biochemical and anatomical parameters were analyzed. Under 15 days in moderate stress condition, the plants initially accumulated soluble sugars and at 30 days, their leaves presented a thicker aquiferous parenchyma, which might facilitate the accumulation of high concentrations of carbohydrates and polyalcohols (sorbitol and mannitol) and perform CAM pathway due to the increase of phosphoenolpyruvate carboxylase (PEPC) activity and accumulate organic acids during the night. Under severe stress CAM was intensified and their leaves were less thick. The results showed that juvenile A. imperialis plants are able to make metabolic adjustments in response to water shortage, and these responses are dependent on the intensity and/or duration of the drought conditions. Overall, this work provides a better understanding of how rupicolous plants survive under different drought conditions. Rupicolous juvenile bromeliads of Alcantarea imperialis subjected to drought are able to survive by increasing the production of sugars under conditions of moderate stress or performing CAM under severe stress.

Identification and characterization of pineapple leaf lncRNAs in crassulacean acid metabolism (CAM) photosynthesis pathway

Long noncoding RNAs (lncRNAs) have been identified in many mammals and plants and are known to play crucial roles in multiple biological processes. Pineapple is an important tropical fruit and a good model for studying the plant evolutionary adaptation to the dry environment and the crassulacean acid metabolism (CAM) photosynthesis strategy; however, the lncRNAs involved in CAM pathway remain poorly characterized. Here, we analyzed the available RNA-seq data sets derived from 26 pineapple leaf samples at 13 time points and identified 2,888 leaf lncRNAs, including 2,046 long intergenic noncoding RNAs (lincRNAs) and 842 long noncoding natural antisense transcripts (lncNATs). Pineapple leaf lncRNAs are expressed in a highly tissue-specific manner. Co-expression analysis of leaf lncRNA and mRNA revealed that leaf lncRNAs are preferentially associated with photosynthesis genes. We further identified leaf lncRNAs that potentially function as competing endogenous RNAs (ceRNAs) of two CAM photosynthesis pathway genes, PPCK and PEPC, and revealed their diurnal expression pattern in leaves. Moreover, we found that 48% of lncRNAs exhibit diurnal expression patterns in leaves, suggesting their important roles in CAM. This study conducted a comprehensive genome-wide analysis of leaf lncRNAs and identified their role in gene expression regulation of the CAM photosynthesis pathway in pineapple.