Effects of trade and poaching pressure on extinction risk for cacti in the Atacama Desert.

In this era of a global biodiversity crisis, vascular plants are facing unprecedented extinction rates. We conducted an assessment of the extinction risk of 32 species and 7 subspecies of Copiapoa, a genus endemic to Chile's fog-dependent coastal Atacama Desert. We applied the International Union for Conservation of Nature Red List Categories and Criteria enhanced by expert insights and knowledge. Our primary aim was to analyze the impact of trade and poaching on their extinction risk. We employed machine learning models, including multinomial logistic regression (MLR), decision tree (DT), and random forest (RF), to analyze the relationships between conservation status and various factors. These factors encompassed trade and poaching activities, landscape condition, human footprint, monthly cloud frequency, and biological traits such as evolutionary distinctiveness and maximum diameter. Seven taxa had an area of occupancy (AOO) of <10 km2, 10 additional taxa had an AOO of <20 km2, and 16 taxa had an AOO of ≤100 km2. This reassessment exposed a critical level of extinction risk for the genus; 92% of the taxa were classified as threatened, 41% as critically endangered, 41% as endangered, and 10% as vulnerable. MLR, DT, and RF exhibited accuracies of 0.784, 0.730, and 0.598, respectively, and identified trade and poaching pressure and landscape condition as the primary drivers of extinction risk. Our assessment of Copiapoa showed trade, poaching, habitat degradation, and their synergic impacts as the main drivers of the genus' extinction risk. Our results highlight the urgent need for nations to develop and enforce strategies to monitor and control trade and poaching pressure because these factors are crucial for the long-term persistence of desert plants.

Retos para la regulación del uso comercial de serpientes elápidas marinas en el Indo­Pacífico Resumen En estos tiempos de la crisis mundial de la biodiversidad, las plantas vasculares enfrentan una tasa de extinción sin precedentes. Evaluamos el riesgo de extinción de 32 especies y siete subespecies de Copiapoa, un género endémico al Desierto de Atacama. Aplicamos los Criterios y Categorías de la Lista Roja de la Unión Internacional para la Conservación de la Naturaleza mejoradas con información y conocimiento de expertos. Nuestro principal objetivo era analizar el impacto del mercado y la colecta ilegal sobre el riesgo de extinción de estas plantas. Usamos modelos de aprendizaje automático, incluyendo la regresión logística multinominal, los árboles de decisión y los bosques aleatorios, para analizar las relaciones entre el estado de conservación y diversos factores. Estos factores englobaron las actividades de mercado y colecta ilegal, condiciones del terreno, huella humana, frecuencia mensual de nubes y características biológicas como la singularidad evolutiva y el diámetro máximo. Siete taxones tuvieron un área de ocupación (ADO) <10 km2, diez taxones más tuvieron ADO <20 km2 y 16 taxones tuvieron ADO ≤100 km2. Este análisis expuso el nivel crítico del riesgo de extinción del género Copiapoa: el 92% de los taxones están clasificados como amenazados, 41% como en peligro crítico, 41% como en peligro y 10% como vulnerable. La regresión logística multinominal, los árboles de decisión y los bosques aleatorios exhibieron una certeza del 0.784, 0.730 y 0.598, respectivamente. También identificaron a la presión del mercado y la colecta ilegal y las condiciones del terreno como los principales factores detrás de riesgo de extinción. Nuestro análisis del género Copiapoa mostró que el mercado, la colecta ilegal, la degradación del hábitat y sus impactos sinérgicos como los principales factores detrás del riesgo de extinción del género. Nuestros resultados resaltan la necesidad urgente de que las naciones desarrollen y apliquen estrategias para monitorear y controlar la presión del mercado y la colecta ilegal pues estos son factores cruciales para la persistencia a largo plazo de las plantas de los desiertos.

The poetry of nitrogen and carbon metabolic shifts: The role of C/N in pitaya phase change.

Pitaya, a desert plant, has an underexplored flowering mechanism due to a lack of functional validation assays. This study reveals that the transition from vegetative to generative growth in pitaya is regulated by significant metabolic shift, underscoring the importance of understanding and address the challenging issue pitaya's phase change. Lateral buds from 6-years-old 'Guanhuahong' pitaya (Hylocereus monacanthus) plants were collected on April 8th, 18th, and 28th 2023, representing early, middle, and late stages of phase transition, respectively. Results showed diminished nitrogen levels concurrent with increased carbon levels and carbon-to-nitrogen (C/N) ratios during pitaya phase transition. Transcriptomic analysis identified batches of differentially expressed genes (DEGs) involved in downregulating nitrogen metabolism and upregulating carbon metabolism. These batches of genes play a central role in the metabolic shifts that predominantly regulate the transition to the generative phase in pitaya. This study unveils the intricate regulatory network involving 6 sugar synthesis and transport, 11 photoperiod (e.g., PHY, CRY, PIF) and 6 vernalization (e.g., VIN3) pathways, alongside 11 structural flowering genes (FCA, FLK, LFY, AGL) out of a vast array of potential candidates in pitaya phase change. These findings provide insights into the metabolic pathways involved in pitaya's phase transition, offering a theoretical framework for managing flowering, guiding breeding strategies to optimize flowering timing and improve crop yields under varied nitrogen conditions.

Reproductive biology as a tool to elucidate taxonomic delimitation: How different can two highly specialized subspecies of Parodia haselbergii (cactaceae) be?

Reproductive isolation is one of the mechanisms of speciation. The two currently accepted subspecies of Parodia haselbergii (P. haselbergii subsp. haselbergii and P. haselbergii subsp. graessneri) were studied regarding flower traits, phenology, breeding systems and pollination. In addition, a principal component analysis with 18 floral characters and germination tests under controlled conditions were performed for both taxa. Pollination was studied in the field, in two localities of Southern Brazil. Pollinators were recorded through photos and film. Breeding system experiments were performed by applying controlled pollinations to plants excluded from pollinators. Both taxa mostly differ in asynchronous flowering periods, floral traits (including floral part measurements and nectar concentration) and pollinators. The flowers of both subspecies are functionally protogynous and perform remarkably long lifespans (≥ 15 days), both traits being novelties for Cactaceae. Whereas the reddish flowers of P. haselbergii subsp. haselbergii (nectar concentration: ca. 18%) are pollinated by hummingbirds of Thalurania glaucopis, the greenish flowers of P. haselbergii subsp. graessneri (nectar concentration: ca. 29%) are pollinated by Augochlora bees (Halictidae). Both subspecies are self-compatible, yet pollinator-dependent. The principal component analysis evidenced that both subspecies are separated, regarding flower traits. The seeds of both subspecies performed differently in the germination tests, but the best results were recovered at 20 °C and germination considerably decreased around 30 °C. In conclusion, all these results support that both taxa are in reproductive isolation, and can be treated as different species.

Comparative transcriptome analysis reveals lineage- and environment-specific adaptations in cacti from the Brazilian Atlantic Forest.

MAIN CONCLUSION: Natural selection influenced adaptive divergence between Cereus fernambucensis and Cereus insularis, revealing key genes governing abiotic stress responses and supporting neoteny in C. insularis. Uncovering the molecular mechanisms driving adaptive divergence in traits related to habitat adaptation remains a central challenge. In this study, we focused on the cactus clade, which includes Cereus sericifer F.Ritter, Cereus fernambucensis Lem., and Cereus insularis Hemsley. These allopatric species inhabit distinct relatively drier regions within the Brazilian Atlantic Forest, each facing unique abiotic conditions. We leveraged whole transcriptome data and abiotic variables datasets to explore lineage-specific and environment-specific adaptations in these species. Employing comparative phylogenetic methods, we identified genes under positive selection (PSG) and examined their association with non-synonymous genetic variants and abiotic attributes through a PhyloGWAS approach. Our analysis unveiled signatures of selection in all studied lineages, with C. fernambucensis northern populations and C. insularis showing the most PSGs. These PSGs predominantly govern abiotic stress regulation, encompassing heat tolerance, UV stress response, and soil salinity adaptation. Our exclusive observation of gene expression tied to early developmental stages in C. insularis supports the hypothesis of neoteny in this species. We also identified genes associated with abiotic variables in independent lineages, suggesting their role as environmental filters on genetic diversity. Overall, our findings suggest that natural selection played a pivotal role in the geographic range of these species in response to environmental and biogeographic transitions.

Comparative analysis of floral transition and floral organ formation in two contrasting species: Disocactus speciosus and D. eichlamii (Cactaceae).

KEY MESSAGE: Contrasting morphologies in Disocactus are the result of differential development of the vegetative and floral tissue where intercalary growth is involved, resulting in a complex structure, the floral axis. Species from the Cactaceae bear adaptations related with their growth in environments under hydric stress. These adaptations have translated into the reduction and modification of various structures such as leaves, stems, lateral branches, roots and the structuring of flowers in a so-called flower-shoot. While cacti flowers and fruits have a consistent structure with showy hermaphrodite or unisexual flowers that produce a fruit called cactidium, the developmental dynamics of vegetative and reproductive tissues comprising the reproductive unit have only been inferred through the analysis of pre-anthetic buds. Here we present a comparative analysis of two developmental series covering the early stages of flower formation and organ differentiation in Disocactus speciosus and Disocactus eichlamii, which have contrasting floral morphologies. We observe that within the areole, a shoot apical meristem commences to grow upward, producing lateral leaves with a spiral arrangement, rapidly transitioning to a floral meristem. The floral meristem produces tepal primordia and a staminal ring meristem from which numerous or few stamens develop in a centrifugal manner in D. speciosus and D. eichlamii, respectively. Also, the inferior ovary derives from the floral meristem flattening and an upward growth of the surrounding tissue of the underlying stem, producing the pericarpel. This structure is novel to cacti and lacks a clear anatomical delimitation with the carpel wall. Here, we present a first study that documents the early processes taking place during initial meristem determination related to pericarpel development and early floral organ formation in cacti until the establishment of mature floral organs.

Adaptations facilitate the invasion of Cylindropuntia rosea (DC.) Backeb. (Cactaceae) in the highlands of southwestern Saudi Arabia.

The colonization and expansion of any plant species into a novel environment depend on its structural and functional characteristics. Therefore, developing better control measures for any invasive plant species requires examining and understanding the mechanisms underlying its reproduction and adaptation to the environment it invades. Recently, a novel exotic species Cylindropuntia rosea (DC.) Backeb. has been identified in Baljurashi, Al-Baha province, in southwestern Saudi Arabia. Reports suggest that this species may become invasive with the current rate of habitat expansion in Baljurashi. Although C. rosea is an important invasive species, most of its morpho-anatomical and physiological characteristics have not been examined. Therefore, the aim of this study was to investigate the morpho-anatomical and related physiological adaptations of C. rosea in its new habitats in the southwestern highlands of Saudi Arabia. We observed that the species is well-equipped for invasion with traits to handle semi-arid conditions, including some morphological and anatomical features, CAM photosynthetic pathway, high growth rate, and highly effective defense mechanisms against herbivores and insects. These morpho-anatomical and physiological characteristics contribute to the high invasiveness of this species in Saudi Arabia.

Elevated extinction risk of cacti under climate change.

Cactaceae (cacti), a New World plant family, is one of the most endangered groups of organisms on the planet. Conservation planning is uncertain as it is unclear whether climate and land-use change will positively or negatively impact global cactus diversity. On the one hand, a common perception is that future climates will be favourable to cacti as they have multiple adaptations and specialized physiologies and morphologies for increased heat and drought. On the other hand, the wide diversity of the more than 1,500 cactus species, many of which occur in more mesic and cooler ecosystems, questions the view that most cacti can tolerate warmer and drought conditions. Here we assess the hypothesis that cacti will benefit and expand in potential distribution in a warmer and more drought-prone world. We quantified exposure to climate change through range forecasts and associated diversity maps for 408 cactus species under three Representative Concentration Pathways (2.6, 4.5 and 8.5) for 2050 and 2070. Our analyses show that 60% of species will experience a reduction in favourable climate, with about a quarter of species exposed to environmental conditions outside of the current realized niche in over 25% of their current distribution. These results show low sensitivity to many uncertainties in forecasting, mostly deriving from dispersal ability and model complexity rather than climate scenarios. While current range size and the International Union for Conservation of Nature's Red List category were not statistically significant predictors of predicted future changes in suitable climate area, epiphytes had the greatest exposure to novel climates. Overall, the number of cactus species at risk is projected to increase sharply in the future, especially in current richness hotspots. Land-use change has previously been identified as the second-most-common driver of threat among cacti, affecting many of the ~31% of cacti that are currently threatened. Our results suggest that climate change will become a primary driver of cactus extinction risk with 60-90% of species assessed negatively impacted by climate change and/or other anthropogenic processes, depending on how these threat processes are distributed across cactus species.

Unraveling the development behind unisexual flowers in Cylindropuntia wolfii (Cactaceae).

BACKGROUND: In certain unisexual flowers, non-functional sexual organs remain vestigial and unisexuality can be overlooked leading to the ambiguous description of the sexual systems. Therefore, to accurately describe the sexual system, detailed morphological and developmental analyses along with experimental crosses must be performed. Cylindropuntia wolfii is a rare cactus endemic to the Sonoran Desert in southern California and northern Baja California that was described as gynodioecious by morphological analysis. The aims of our project include accurately identifying the sexual system of C. wolfii using histological and functional studies and characterizing the developmental mechanisms that underlie its floral development. METHODS: Histological analyses were carried out on different stages of C. wolfii flowers and controlled crosses were performed in the field. RESULT: Our results identified C. wolfii to be functionally dioecious. The ovule and anther development differed between staminate and pistillate flowers. In vivo pollen germination tests showed that the pollen of staminate and pistillate flowers were viable and the stigma and style of both staminate and pistillate flowers were receptive. This suggests that there are no genetic or developmental barriers in the earlier stages of pollen recognition and pollen germination. CONCLUSIONS: Despite being functionally dioecious, we observed that functionally pistillate individuals produced fruits with a large number of aborted seeds. This implies that not only does this species have low reproductive success, but its small population sizes may lead to low genetic diversity.

Evolution of flower allometry and pigmentation in Mammillaria haageana (Cactaceae).

BACKGROUND: A puzzle in evolution is the understanding of how the environment might drive subtle phenotypic variation, and whether this variation is adaptive. Under the neutral evolutionary theory, subtle phenotypes are almost neutral with little adaptive value. To test this idea, we studied the infraspecific variation in flower shape and color in Mammillaria haageana, a species with a wide geographical distribution and phenotypic variation, which populations are often recognized as infraspecific taxa. RESULTS: We collected samples from wild populations, kept them in the greenhouse for at least one reproductive year, and collected newly formed flowers. Our first objective was to characterize tepal natural variation in M. haageana through geometric morphometric and multivariate pigmentation analyses. We used landmark-based morphometrics to quantify the trends of shape variation and tepal color-patterns in 20 M. haageana accessions, belonging to five subspecies, plus 8 M. albilanata accessions for comparison as the sister species. We obtained eight geometric morphometric traits for tepal shape and color-patterns. We found broad variation in these traits between accessions belonging to the same subspecies, without taxonomic congruence with those infraspecific units. Also the phenetic cluster analysis showed different grouping patterns among accessions. When we correlated these phenotypes to the environment, we also found that solar radiation might explain the variation in tepal shape and color, suggesting that subtle variation in flower phenotypes might be adaptive. Finally we present anatomical sections in M. haageana subsp. san-angelensis to propose some of the underlying tepal structural features that may give rise to tepal variation. CONCLUSIONS: Our geometric morphometric approach of flower shape and color allowed us to identify the main trends of variation in each accession and putative subspecies, but also allowed us to correlate these variation to the environment, and propose anatomical mechanisms underlying this diversity of flower phenotypes.

Influence of competition and intraguild predation between two candidate biocontrol parasitoids on their potential impact against Harrisia cactus mealybug, Hypogeococcus sp. (Hemiptera: Pseudococcidae).

When two or more parasitoid species, particularly candidates for biocontrol, share the same target in the same temporal window, a complex of behaviors can occur among them. We studied the type of interactions (competition and intraguild predation) that existed between the nymphal parasitoids Anagyrus cachamai and A. lapachosus (Hymenoptera: Encyrtidae), two candidate neoclassical biocontrol agents against the Puerto Rican cactus pest mealybug, Hypogeococcus sp. (Hemiptera: Pseudococcidae). The surrogate native congener host in Argentina, the cactus mealybug Hypogeococcus sp., was studied to predict which species should be released; in the case that both should be released, in which order, and their potential impact on host suppression. In the laboratory we conducted experiments where different densities of the host mealybug were exposed to naive females of A. cachamai and A. lapachosus sequentially in both directions. Experiments were analyzed by combining a series of competitive behavioral and functional response models. A fully Bayesian approach was used to select the best explaining models and calculate their parameters. Intraguild predation existed between A. cachamai, the species that had the greatest ability to exploit the resource, and A. lapachosus, the strongest species in the interference competition. The role that intraguild predation played in suppression of Hypogeococcus sp. indicated that a multiple release strategy for the two biocontrol agents would produce better control than a single release; as for the release order, A. lapachosus should be released first.

Grafting in Hylocereus (Cactaceae) as a tool for strengthening tolerance to high temperature stress.

The Hylocereus species that are grown as exotic fruit crops are very often farmed under marginal agronomic conditions, which may include exposure to high temperatures. Here we present a pioneering investigation of grafting as an agro-technique to improve heat tolerance in Hylocereus. To this end, we studied the diploid species H. undatus, the tetraploid H. megalanthus and its di-haploid gamete-derived line 2719, and the interspecific-interploid tetraploid Z-10, all grafted onto H. undatus as the rootstock. Self-grafted, grafted and non-grafted plants were acclimated for one week (to obtain baseline values) and then exposed to heat stress (45/35 °C day/night) for three days, followed by a one-week recovery period under optimal temperatures (30/22 °C). A comparison of the physiological, biochemical and molecular performances of the grafted and self-grafted plants under heat stress and during the recovery period vs those of non-stressed plants (control; 30/22 °C) showed that the grafted and self-grafted plants performed better in most of the assessments: grafted and self-grafted plants recovered more rapidly from the heat stress and suffered far less stem damage. An unexpected - but important - finding that may have implications for other crop was that the self-grafted plants showed better performance than non-grafted plants throughout the trial. Our findings provide support for grafting as a strategy for coping with the stress induced by extremely high temperatures. This study thus paves the way for further investigations of grafting in Hylocereus as a valuable technique that will maintain crop productivity in the face of increasing worldwide temperatures.

Modeling the potential distribution of Epiphyllum phyllanthus (L.) Haw. under future climate scenarios in the Caatinga biome.

The climate change projections for the Caatinga biome this century are for an increase in temperature and reduction in rainfall, leading to aridization and plant cover dominated by Cactaceae. The objective of this study was to model the potential distribution of Epiphyllum phyllanthus (L.) Haw., a cactus that is native to the Caatinga biome, considering two possible future climate scenarios, to assess this species' spatio-temporal response to these climate change, and thus to evaluate the need or not for conservation measures. For this purpose, we obtained biogeographic information on the target species from biodiversity databases, choosing nine environmental variables and applying the MaxEnt algorithm. We considered the time intervals 2041-2060 and 2061-2080, centered on 2050 and 2070, respectively, and the greenhouse gas scenarios RCP4.5 and 8.5. For all the scenarios considered, the models generated for 2050 and 2070 projected drastic contraction (greater than 80%) for the areas of potential occurrence of the species in relation to the present potential. The remaining areas were found to be concentrated in the northern portion of the biome, specifically in the northern part of the state of Ceará, which has particular characteristics.

Performance of Hylocereus (Cactaceae) species and interspecific hybrids under high-temperature stress.

High temperatures limit the successful cultivation of the Hylocereus species on a global basis. We aimed to investigate the degree of heat tolerance in three species, namely, the diploids Hylocereus undatus and H. monacanthus, and the tetraploid H. megalanthus, and nine of their interspecific-interploid hybrids. Rooted cuttings were exposed to heat stress (45/35 °C) or control conditions (25/20 °C) for eight days. Initially, the plants were screened for their tolerance to heat stress and ranked into four heat tolerance categories: good tolerance, moderate tolerance, low tolerance, or sensitive, according to the decrease in the maximum quantum efficiency of photosystem II (Fv/Fm) and visual stem damage. The physiological and biochemical performances of the parental species and of three hybrids representing three different heat-tolerance categories were further analyzed in depth. H. megalanthus (classified as heat sensitive) showed a 65% decrease in Fv/Fm and severe visual stem damage, along with a marked reduction in total chlorophyll content, a large increase in malondialdehyde, and inhibition of catalase activity. H. undatus and H. monacanthus, (classified as low-tolerance species) exhibited slight stem "liquification." The good-tolerance hybrid Z-16 exhibited the best performance under heat stress (21% decrease in Fv/Fm) and the absence of stem damage, coupled with a small decrease in total chlorophyll content, a slight increase in malondialdehyde, high antioxidant activity, and proline accumulation progressing with time. Our findings revealed that most of the hybrids performed better than their parental species, indicating that our breeding programs can provide Hylocereus cultivars suitable for cultivation in heat-challenging regions.

Differential responses of the soil microbial community in two pitaya orchards with different mulch types.

To prevent plants from being damaged due to extreme temperature and sunlight, the pitaya orchards in Hainan Province, China, are increasingly adopting living and black fabric cloth mulching. In this study, an Illumina Hiseq sequencer was employed to compare the soil microbial communities of two pitaya orchards, one covered by living mulching (LM) and the other covered by black fabric cloth (FC). Bacterial abundance was higher in the LM orchard than in the FC orchard (1.19 × 104 versus 4.49 × 104 g-1 soil). In contrast, fungal abundance was higher in the FC orchard than in the LM orchard (2.71 × 106 versus 2.97 × 105 g-1 soil). We also found that the most dominant species in the FC orchard were from the genus Neoscytalidium, which included species that could cause infection in a large variety of plant hosts. However, the LM orchard mainly harbored useful fungal species, such as Trichoderma and Chaetomium. Soil nutrients were positively correlated in the FC orchard, which potentially indicated that the FC orchard could demonstrate better fertilizer utilization efficiency. However, the LM and FC strategies have both advantages and disadvantages with regards to the cultivation management of pitaya orchards.

Giant cacti: isotopic recorders of climate variation in warm deserts of the Americas.

The plant family Cactaceae is considered among the most threatened groups of organisms on the planet. The threatened status of the cacti family has created a renewed interest in the highly evolved physiological and morphological traits that underpin their persistence in some of the harshest subtropical environments in the Americas. Among the most important anatomical features of cacti is the modification of leaves into spines, and previous work has shown that the stable isotope chemistry of cacti spines records potential variations in stem water balance, stress, and Crassulacean acid metabolism (CAM). We review the opportunities, challenges, and pitfalls in measuring δ 13C, δ 2H, and δ 18O ratios captured in spine tissues that potentially reflect temporal and spatial patterns of stomatal conductance, internal to atmospheric CO2 partial pressures, and subsequent patterns of photosynthetic gas exchange. We then evaluate the challenges in stable isotope analysis in spine tissues related to variation in CAM expression, stem water compartmentalization, and spine whole-tissue composition among other factors. Finally, we describe how the analysis of all three isotopes can be used in combination to provide potentially robust analysis of photosynthetic function in cacti, and other succulent-stemmed taxa across broad spatio-temporal environmental gradients.

Conserved miR396b-GRF Regulation Is Involved in Abiotic Stress Responses in Pitaya (Hylocereus polyrhizus).

MicroRNA396 (miR396) is a conserved microRNA family that targets growth-regulating factors (GRFs), which play significant roles in plant growth and stress responses. Available evidence justifies the idea that miR396-targeted GRFs have important functions in many plant species; however, no genome-wide analysis of the pitaya (Hylocereus polyrhizus) miR396 gene has yet been reported. Further, its biological functions remain elusive. To uncover the regulatory roles of miR396 and its targets, the hairpin sequence of pitaya miR396b and the open reading frame (ORF) of its target, HpGRF6, were isolated from pitaya. Phylogenetic analysis showed that the precursor miR396b (MIR396b) gene of plants might be clustered into three major groups, and, generally, a more recent evolutionary relationship in the intra-family has been demonstrated. The sequence analysis indicated that the binding site of hpo-miR396b in HpGRF6 is located at the conserved motif which codes the conserved "RSRKPVE" amino acid in the Trp-Arg-Cys (WRC) region. In addition, degradome sequencing analysis confirmed that four GRFs (GRF1, c56908.graph_c0; GRF4, c52862.graph_c0; GRF6, c39378.graph_c0 and GRF9, c54658.graph_c0) are hpo-miR396b targets that are regulated by specific cleavage at the binding site between the 10th and 11th nucleotides from the 5' terminus of hpo-miR396b. Furthermore, quantitative real-time polymerase chain reaction (qRT-PCR) analysis showed that hpo-miR396b is down-regulated when confronted with drought stress (15% polyethylene glycol, PEG), and its expression fluctuates under other abiotic stresses, i.e., low temperature (4 ± 1 °C), high temperature (42 ± 1 °C), NaCl (100 mM), and abscisic acid (ABA; 0.38 mM). Conversely, the expression of HpGRF6 showed the opposite trend to exposure to these abiotic stresses. Taken together, hpo-miR396b plays a regulatory role in the control of HpGRF6, which might influence the abiotic stress response of pitaya. This is the first documentation of this role in pitaya and improves the understanding of the molecular mechanisms underlying the tolerance to drought stress in this fruit.

A decade of flowering phenology of the keystone saguaro cactus (Carnegiea gigantea).

PREMISE OF THE STUDY: Phenology is the study of biological life cycle events, such as flowering and migration. Climate patterns can alter these life history events, having ecosystem-wide ramifications. For example, warmer springs are associated with earlier leaf-out for many species, impacting species interactions and growing-season carbon dynamics. While phenological research has been conducted extensively in temperate regions, relatively little is known about the phenological responses in arid and semi-arid regions. METHODS: In this study we looked at the flowering phenology of a keystone species in the Sonoran Desert, the saguaro cactus (Carnegiea gigantea). The timing and abundance of flowering was observed on 151 individuals for 10 years at a site near Tucson, Arizona, USA. Using six phenological traits, we explored the relationship between saguaro size and flowering and the climatic drivers of flowering. KEY RESULTS: Our analyses demonstrated how the calculation of phenological traits at the individual versus the population level can yield differing responses to climate variability, suggesting that not all studies examining the same trait (e.g., first day of bloom) are directly comparable. We found that larger cacti began flowering earlier, flowered for longer, and produced more flowers. Warmer temperatures were correlated with advanced onset and higher bloom yields, while increased precipitation appeared to delay onset and reduce bloom yields. CONCLUSIONS: Given that climate models predict that the Southwestern USA will become increasingly warmer with more variable precipitation, saguaros may begin flowering earlier in the season and flower more intensely, which could impact pollen availability and population dynamics.

Genomic changes associated with adaptation to arid environments in cactophilic Drosophila species.

BACKGROUND: Insights into the genetic capacities of species to adapt to future climate change can be gained by using comparative genomic and transcriptomic data to reconstruct the genetic changes associated with such adaptations in the past. Here we investigate the genetic changes associated with adaptation to arid environments, specifically climatic extremes and new cactus hosts, through such an analysis of five repleta group Drosophila species. RESULTS: We find disproportionately high rates of gene gains in internal branches in the species' phylogeny where cactus use and subsequently cactus specialisation and high heat and desiccation tolerance evolved. The terminal branch leading to the most heat and desiccation resistant species, Drosophila aldrichi, also shows disproportionately high rates of both gene gains and positive selection. Several Gene Ontology terms related to metabolism were enriched in gene gain events in lineages where cactus use was evolving, while some regulatory and developmental genes were strongly selected in the Drosophila aldrichi branch. Transcriptomic analysis of flies subjected to sublethal heat shocks showed many more downregulation responses to the stress in a heat sensitive versus heat resistant species, confirming the existence of widespread regulatory as well as structural changes in the species' differing adaptations. Gene Ontology terms related to metabolism were enriched in the differentially expressed genes in the resistant species while terms related to stress response were over-represented in the sensitive one. CONCLUSION: Adaptations to new cactus hosts and hot desiccating environments were associated with periods of accelerated evolutionary change in diverse biochemistries. The hundreds of genes involved suggest adaptations of this sort would be difficult to achieve in the timeframes projected for anthropogenic climate change.

Transcriptional activation of long terminal repeat retrotransposon sequences in the genome of pitaya under abiotic stress.

Frequent somatic variations exist in pitaya (Hylocereus undatus) plants grown under abiotic stress conditions. Long terminal repeat (LTR) retrotransposons can be activated under stressful conditions and play key roles in plant genetic variation and evolution. However, whether LTR retrotransposons promotes pitaya somatic variations by regulating abiotic stress responses is still uncertain. In this study, transcriptionally active LTR retrotransposons were identified in pitaya after exposure to a number of stress factors, including in vitro culturing, osmotic changes, extreme temperatures and hormone treatments. In total, 26 LTR retrotransposon reverse transcriptase (RT) cDNA sequences were isolated and identified as belonging to 9 Ty1-copia and 4 Ty3-gypsy families. Several RT cDNA sequences had differing similarity levels with RTs from pitaya genomic DNA and other plant species, and were differentially expressed in pitaya under various stress conditions. LTR retrotransposons accounted for at least 13.07% of the pitaya genome. HuTy1P4 had a high copy number and low expression level in young stems of pitaya, and its expression level increased after exposure to hormones and abiotic stresses, including in vitro culturing, osmotic changes, cold and heat. HuTy1P4 may have been subjected to diverse transposon events in 13 pitaya plantlets successively subcultured for four cycles. Thus, the expression levels of these retrotransposons in pitaya were associated with stress responses and may be involved in the occurrence of the somaclonal variation in pitaya.

Host Plant Adaptation in Cactophilic Species of the Drosophila buzzatii Cluster: Fitness and Transcriptomics.

Host plant shifts in herbivorous insects often involve facing new environments that may speed up the evolution of oviposition behavior, performance-related traits, morphology, and, incidentally, reproductive isolation. In the genus Drosophila, cactophilic species of the repleta group include emblematic species in the study of the evolution of host plant utilization. The South American D. buzzatii and its sibling D. koepferae are a model system for the study of differential host plant use. Although these species exhibit a certain degree of niche overlap, the former breeds primarily on decaying cladodes of Opuntia cacti while D. koepferae main hosts are columnar cacti of the genus Trichocereus. Opuntia sulphurea and Trichocereus terscheckii are among the main hosts in nature. These cacti differ in ecological (spatial and temporal predictability) and chemical characteristics. Particularly relevant is the presence of toxic alkaloids in T. terscheckii. Studies of the effects of these cacti and alkaloids revealed the remarkable impact on oviposition behavior, viability, developmental time, wing morphology, mating success, and developmental stability in both species. Recent whole-genome expression studies showed that expression profiles are massively affected by the rearing cactus, and that the presence of alkaloids is the main factor modulating gene expression in D. buzzatii. Functional enrichment analysis indicated that differentially expressed genes are related to detoxification processes and stress response-though genes involved in development are an important part of the transcriptomic response. The implications of our studies in the evolution of host plant use in the repleta group are discussed.