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An overlooked phenomenon is a potential increase in the distribution and abundance of plants with the highly water-usage-efficient crassulacean acid metabolism (CAM). In the present article, we critically analyze recent research to investigate to what extent and why CAM plants may have recently expanded their range and abundance under global change. We discuss the ecophysiological and evolutionary mechanisms linked with CAM succulence and the drivers underlying potential CAM expansion, including drought, warming, and atmospheric carbon dioxide enrichment. We further map the biogeographic pattern of CAM expansion and show that some CAM plants (e.g. Cylindropuntia, Opuntia, and Agave) are expanding and encroaching within dryland landscapes worldwide. Our results collectively highlight the recent expansion of CAM plants, a trend that could be sustained under increasing aridity with climate change. We recommend that CAM expansion be evaluated in a data-model integrated framework to better understand and predict the ecological and socioeconomic consequences of CAM expansion during the Anthropocene. [ABSTRACT FROM AUTHOR]

Temperature shapes the geographical distribution and behavior of plants. Understanding the regulatory mechanisms underlying the plant heat stress response is important for developing climate-resilient crops, including maize (Zea mays). To identify transcription factors (TFs) that may contribute to the maize heat stress response, we generated a dataset of short- and long-term transcriptome changes following a heat treatment time course in the inbred line B73. Co-expression network analysis highlighted several TFs, including the class B2a heat shock factor (HSF) ZmHSF20. Zmhsf20 mutant seedlings exhibited enhanced tolerance to heat stress. Furthermore, DNA affinity purification sequencing and Cleavage Under Targets and Tagmentation assays demonstrated that ZmHSF20 binds to the promoters of Cellulose synthase A2 (ZmCesA2) and three class A Hsf genes, including ZmHsf4, repressing their transcription. We showed that ZmCesA2 and ZmHSF4 promote the heat stress response, with ZmHSF4 directly activating ZmCesA2 transcription. In agreement with the transcriptome analysis, ZmHSF20 inhibited cellulose accumulation and repressed the expression of cell wall-related genes. Importantly, the Zmhsf20 Zmhsf4 double mutant exhibited decreased thermotolerance, placing ZmHsf4 downstream of ZmHsf20. We proposed an expanded model of the heat stress response in maize, whereby ZmHSF20 lowers seedling heat tolerance by repressing ZmHsf4 and ZmCesA2, thus balancing seedling growth and defense. The transcription factor ZmHSF20 acts upstream of ZmHsf4 and Cellulose synthase A2, which positively regulate cell wall development under heat stress, thereby improving maize heat tolerance. [ABSTRACT FROM AUTHOR]

In heterotrophs, heme degradation produces bilirubin, a tetrapyrrole compound that has antioxidant activity. In plants, heme is degraded in plastids and is believed to be converted to phytochromobilin rather than bilirubin. Recently, we used the bilirubin-inducible fluorescent protein UnaG to reveal that plants produce bilirubin via a non-enzymatic reaction with NADPH. In the present study, we used an UnaG-based live imaging system to visualize bilirubin accumulation in Arabidopsis thaliana and Nicotiana benthamiana at the organelle and tissue levels. In chloroplasts, bilirubin preferentially accumulated in the stroma, and the stromal bilirubin level increased upon dark treatment. Investigation of intracellular bilirubin distribution in leaves and roots showed that it accumulated mostly in plastids, with low levels detected in the cytosol and other organelles, such as peroxisomes, mitochondria and the endoplasmic reticulum. A treatment that increased bilirubin production in chloroplasts decreased the bilirubin level in peroxisomes, implying that a bilirubin precursor is transported between the two organelles. At the cell and tissue levels, bilirubin showed substantial accumulation in the root elongation region but little or none in the root cap and guard cells. Intermediate bilirubin accumulation was observed in other shoot and root tissues, with lower levels in shoot tissues. Our data revealed the distribution of bilirubin in plants, which has implications for the transport and physiological function of tetrapyrroles. [ABSTRACT FROM AUTHOR]

Background and Aims Quantifying spatial species richness is useful to describe biodiversity patterns across broad geographical areas, especially in large, poorly known plant groups. We explore patterns and predictors of species richness across Africa in one such group, the palaeotropical genus Grewia L. (Malvaceae). Methods Grewia species richness was quantified by extracting herbarium records from GBIF and Tropicos and creating geographical grids at varying spatial scales. We assessed predictors of species richness using spatial regression models with 30 environmental variables. We explored species co-occurrence in Madagascar at finer resolutions using Schoener's index and compared species range sizes and International Union for Conservation of Nature status among ecoregions. Lastly, we derived a trait matrix for a subset of species found in Madagascar to characterize morphological diversity across space. Key Results Grewia species occur in 50 countries in Africa, with the highest number of species in Madagascar (93, with 80 species endemic). Species richness is highest in Madagascar, with ≤23 Grewia species in a grid cell, followed by coastal Tanzania/Kenya (≤13 species) and northern South Africa and central Angola (11 species each). Across Africa, higher species richness was predicted by variables related to aridity. In Madagascar, a greater range in environmental variables best predicted species richness, consistent with geographical grid cells of highest species richness occurring near biome/ecoregion transitions. In Madagascar, we also observe increasing dissimilarity in species composition with increasing geographical distance. Conclusions The spatial patterns and underlying environmental predictors that we uncover in Grewia represent an important step in our understanding of plant distribution and diversity patterns across Africa. Madagascar boasts nearly twice the Grewia species richness of the second most species-rich country in Africa, which might be explained by complex topography and environmental conditions across small spatial scales. [ABSTRACT FROM AUTHOR]

Low temperature constitutes one of the main barriers to plant distributions, confining many clades to their ancestrally tropical biome. However, recent evidence suggests that transitions from tropical to temperate biomes may be more frequent than previously thought. Here, we study the evolution of cold and frost tolerance in the globally distributed and highly stress-tolerant Salicornieae (Salicornioideae, Amaranthaceae s.l.). We first generate a phylogenetic tree comprising almost all known species (85-90%), using newly generated (n  = 106) and published nuclear-ribosomal and plastid sequences. Next, we use geographical occurrence data to document in which clades and geographical regions cold-tolerant species occur and reconstruct how cold tolerance evolved. Finally, we test for correlated evolution between frost tolerance and the annual life form. We find that frost tolerance has evolved independently in up to four Northern Hemisphere lineages but that annuals are no more likely to evolve frost tolerance than perennials, indicating the presence of different strategies for adapting to cold environments. Our findings add to mounting evidence for multiple independent out-of-the-tropics transitions among close relatives of flowering plants and raise new questions about the ecological and physiological mechanism(s) of adaptation to low temperatures in Salicornieae. [ABSTRACT FROM AUTHOR]

Invasive plants are often sold as ornamental garden plants, but how often are species sold in the same locations as where they are invasive? To answer this question, we assessed the geography of ornamental plant sales in the United States in relation to existing invasions and potential invasion risk with climate change. Using a data set of 672 nurseries selling 89 invasive plants, we estimated the distance between nursery sales and invasive species' observed distributions. We also used species range maps to identify nursery sales within current potential invaded ranges, as well as within species' future potential ranges given climate change. Half of the species were sold by a nursery within 21 kilometers of an observed record of invasion. Under the current climate, horticulture could be seeding invasions for 73 of the 89 species studied, and horticulture could facilitate climate-driven range expansion of 25 of 89 species. Our results illustrate risks associated with horticultural introductions of invasive species, providing guidance for regulatory and educational interventions that reduce the spread of ongoing and future invasions. [ABSTRACT FROM AUTHOR]

Low temperature is one of the most important abiotic factors limiting the growth, development and geographical distribution of plants. Prunus mume is an attractive woody ornamental plant that blooms in early spring in Beijing. However, the molecular mechanisms underlying cold hardening to enhance freezing tolerance in Prunus genus remains elusive. This study examined the dynamic physiological responses induced by cold hardening, and identified freezing-tolerance genes by RNA-seq and ATAC-seq analyses. Cold hardening elevated the content of soluble substances and enhanced freezing resistance in P. mume. Transcriptome analysis indicated that the candidate differentially expressed genes (DEGs) were those enriched in Ca2+ signalling, mitogen-activated protein kinase (MAPK) cascade, abscisic acid signalling, and inducer of CBF expression 1 (ICE)-C-repeat binding factor (CBF) signalling pathways. The openness of gene chromatin positively correlated with the expression level of these genes. Thirteen motifs were identified in the open chromatin regions in the treatment group subjected to freezing after cold hardening. The chromatin opening of transcription start site at the proximal –177 region of cold-shock protein CS120-like (PmCSL) was markedly increased, while the expression level of PmCSL was significantly up-regulated. Overexpression of PmCSL in Arabidopsis significantly improved the freezing tolerance of transgenic plants. These findings provide new insights into the regulatory mechanism of freezing tolerance to improve breeding of cold-hardy P. mume plants. [ABSTRACT FROM AUTHOR]

Increasing evidence indicates that wide distributed bryophyte taxa with homogeneous morphology may represent separate evolutionary lineages. The evolutionary histories of these cryptic lineages may be related to historical factors, such as the climatic oscillations in the Quaternary. Thus, the post-glacial demographic signatures paired with cryptic speciation may result in complex phylogeographic patterns. This research has two aims: to determine whether the widespread moss Racomitrium lanuginosum represents cryptic molecular taxa across the Northern Hemisphere and to infer the effects of Quaternary glaciations on spatial genetic diversity. We used the internal transcribed spacer (ITS) marker to resolve the phylogeographic history of the species and single nucleotide polymorphisms (genotyping-by-sequencing) to infer the genetic structure and demographic history. Finally, we assessed the historical changes in the distribution range using species distribution models. Racomitrium lanuginosum comprises distinct molecular lineages sympatrically distributed in the Northern Hemisphere. We also uncovered long-distance dispersal from eastern North America to Scandinavia and potential in situ survival in northern Scandinavia. Due to the genetic signatures, the Alaska Peninsula could be considered a glacial refugium. The species experienced post-glacial expansion northwards in the Northern Hemisphere, mainly from the Alaska Peninsula. Our results exemplify the complex phylogeographic history in cold environments and contribute to recognizing evolutionary patterns in the Northern Hemisphere. [ABSTRACT FROM AUTHOR]

Solar-induced fluorescence (SIF) is a promising proxy for photosynthesis, but it is unclear whether it performs well in tracking the gross primary productivity (GPP) under different environmental conditions. In this study, we investigated the dynamics of the two parameters from October 2020 to June 2021 in field-grown winter wheat (Triticum aestivum) and found that the ability of SIF to track GPP was weakened at low temperatures. Accounting for the coupling of light and temperature at a seasonal scale, we found that SIF yield showed a lower temperature sensitivity and had a lower but broader optimal temperature range compared with light-use efficiency (LUE), although both SIF yield and LUE decreased in low-temperature conditions. The discrepancy between the temperature responses of SIF yield and GPP caused an increase in the ratio of SIF/GPP in winter, which indicated the variation in the relationship between them during this period. The results of our study highlight the impact of low temperature on the relationship between SIF and GPP and show the necessity of reconsidering the dynamics of energy distribution inside plants under changing environments. [ABSTRACT FROM AUTHOR]

Members of the B family of membrane-bound ATP-binding cassette (ABC) transporters represent key components of the auxin efflux machinery in plants. Over the last two decades, experimental studies have shown that modifying ATPbinding cassette sub-family B (ABCB) expression affects auxin distribution and plant phenotypes. However, precisely how ABCB proteins transport auxin in conjunction with the more widely studied family of PIN-formed (PIN) auxin efflux transporters is unclear, and studies using heterologous systems have produced conflicting results. Here, we integrate ABCB localization data into a multicellular model of auxin transport in the Arabidopsis thaliana root tip to predict how ABCB-mediated auxin transport impacts organ-scale auxin distribution. We use our model to test five potential ABCB-PIN regulatory interactions, simulating the auxin dynamics for each interaction and quantitatively comparing the predictions with experimental images of the DII-VENUS auxin reporter in wild-type and abcb single and double loss-offunction mutants. Only specific ABCB-PIN regulatory interactions result in predictions that recreate the experimentally observed DII-VENUS distributions and long-distance auxin transport. Our results suggest that ABCBs enable auxin efflux independently of PINs; however, PIN-mediated auxin efflux is predominantly through a co-dependent efflux where colocalized with ABCBs. [ABSTRACT FROM AUTHOR]

Flowering time is an important agronomic trait that determines the distribution and adaptation of plants. The accurate prediction of flowering time in elite germplasm is critical for maize breeding. However, the molecular mechanisms underlying the photoperiod response remain elusive in maize. Here we cloned the flowering time-controlling gene, ZmNF-YC2 , by map-based cloning and confirmed that ZmNF-YC2 is the nuclear transcription factor Y subunit C-2 protein and a positive regulator of flowering time in maize under long-day conditions. Our results show that ZmNF-YC2 promotes the expression of ZmNF-YA3. ZmNF-YA3 negatively regulates the transcription of ZmAP2. ZmAP2 suppresses the expression of ZMM4 to delay flowering time. We then developed a gene regulatory model of flowering time in maize using ZmNF-YC2 , ZmNF-YA3 , ZmAP2 , ZMM4 , and other key genes. The cascading regulation by ZmNF-YC2 of maize flowering time has not been reported in other species. [ABSTRACT FROM AUTHOR]

Pathogen specialization may not always arise due to an adaptive trade‐off between infecting one or many species. Bruns et al. characterized the potential host range of four lineages of the fungal pathogen Microbotryum on three Dianthus species. They found that both generalists and specialists co‐occurred in nature and no clear fitness benefit is found for either. They suggested that specialization may be related to the specific geographic distribution of these plants. [ABSTRACT FROM AUTHOR]