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Starch serves functions that range over a timescale of minutes to years, according to the cell type from which it is derived. In guard cells, starch is rapidly mobilized by the synergistic action of β-AMYLASE1 (BAM1) and α-AMYLASE3 (AMY3) to promote stomatal opening. In the leaves, starch typically accumulates gradually during the day and is degraded at night by BAM3 to support heterotrophic metabolism. During osmotic stress, starch is degraded in the light by stress-activated BAM1 to release sugar and sugar-derived osmolytes. Here, we report that AMY3 is also involved in stress-induced starch degradation. Recently isolated Arabidopsis thaliana amy3 bam1 double mutants are hypersensitive to osmotic stress, showing impaired root growth. amy3 bam1 plants close their stomata under osmotic stress at similar rates as the wild type but fail to mobilize starch in the leaves. 14C labeling showed that amy3 bam1 plants have reduced carbon export to the root, affecting osmolyte accumulation and root growth during stress. Using genetic approaches, we further demonstrate that abscisic acid controls the activity of BAM1 and AMY3 in leaves under osmotic stress through the AREB/ABF-SnRK2 kinase-signaling pathway. We propose that differential regulation and isoform subfunctionalization define starch-adaptive plasticity, ensuring an optimal carbon supply for continued growth under an ever-changing environment.

The Eastern Tropical Pacific (ETP) Spotted Eagle Ray, Aetobatus laticeps Gill, 1865, is an understudied species with limited information on its ecology and conservation status. Only in the last 10 years has this lineage been re-described as a distinct species from the formerly widespread Aetobatus narinari species complex (Euphrasen, 1790) (ANSC). The sampling in the studies that divided the ANSC was not geographically balanced, with most individuals (50) collected from the Atlantic and only (5) from the ETP. Given the vast extent and environmental heterogeneity of this region, it is possible that a significant portion of the genus’s genetic variation, and possibly even the presence of undescribed species, is being overlooked. Because eagle rays have relatively low fecundity and are subject to targeted and incidental fisheries, they are highly susceptible to population declines. Consequently, elucidating the genetic diversity, distribution range, genetic variability and interconnectivity of this species is crucial to assess its conservation status correctly. Through a mixed genetic marker approach, we assessed ETP eagle rays’ phylogeny, genetic diversity and phylogeography. First, we confirmed that eagle rays in this region correspond to A. laticeps. Second, we found low levels of genetic variability across all markers, coupled with a high degree of geographic-genetic structure. Finally, our data suggested three potential mechanisms that could explain the population structure we encountered: a) Isolation by distance b) Isolation by philopatry, and c) Isolation by depth. To date, this is the first comprehensive study of the genetic diversity of eagle rays in the Eastern Tropical Pacific, shedding light on a species that has long been overlooked. Our findings suggest that this species is more susceptible to direct and bycatch fishing pressures, as well as other indirect human impacts. Therefore, we recommend a re-evaluation of the conservation status of this species.

The accumulation of starch within photosynthetic tissues and within dedicated storage organs has been characterized extensively in many species, and a function in buffering carbon availability or in fueling later growth phases, respectively, has been proposed. However, developmentally regulated starch turnover within heterotrophic tissues other than dedicated storage organs is poorly characterized, and its function is not well understood. Here, we report on the characterization of starch turnover during flower, early embryo, and silique development in Arabidopsis (Arabidopsis thaliana) using a combined clearing-staining technique on whole-mount tissue. Besides the two previously documented waves of transient starch accumulation in the stamen envelope, occurring during meiosis and pollen mitosis I, we identified a novel, third wave of starch amylogenesis/amylolysis during the last stages of stamen development. To gain insights into the underlying molecular mechanisms, we analyzed publicly available microarray data, which revealed a developmentally coordinated expression of carbohydrate transport and metabolism genes during these waves of transient starch accumulation. Based on this analysis, we characterized starch dynamics in mutants affecting hexose phosphate metabolism and translocation, and identified the Glc-6-phosphate/phosphate antiporter GPT1 as the putative translocator of Glc-6-phosphate for starch biosynthesis in reproductive tissues. Based on these results, we propose a model of starch synthesis within the pollen grain and discuss the nutrient transport route feeding the embryo within the developing seed.

Páez-Rosas et al discuss the unprecedented records of Guadalupe and Juan Fernández fur seals in the Galapagos Archipelago. The Guadalupe fur seal (GFS) and Juan Fernández fur seal (JFFS) have a restricted distribution to islands in the North and South Pacific Ocean, respectively. GFS only breeds in Mexico, concentrating its population on Guadalupe and the San Benito Islands with a regional abundance of around 40,000 individuals while JFFS is limited to the Juan Fernández Archipelago in Chile with an estimated population of 20,000 animals. Both species were considered extinct by the end of the 1800s because of intense commercial hunting. However, a small number of GFS and JFFS were discovered breeding on Guadalupe Island in 1954 and Alejandro Selkirk Island in 1965, respectively. These populations grew slowly and colonized other nearby islands over time surviving in caves or on inaccessible beaches, thereby maintaining their populations and probably facilitating the increase of their genetic diversity. Here, the extralimital records of GFS and JFFS in the Eastern Tropical Pacific which occurred during the incidence of seasonal Humboldt Current near the Galapagos Archipelago when the proliferation of nutrients increases at the base of the region's food marine web is reported.

Cadmium (Cd) toxicity has been widely studied in different plant species; however, the mechanism involved in its toxicity as well as the cell response against the metal have not been well established. In this work, using pea (Pisum sativum) plants, we studied the effect of Cd on antioxidants, reactive oxygen species (ROS), and nitric oxide (NO) metabolism of leaves using different cellular, molecular, and biochemical approaches. The growth of pea plants with 50 μM CdCl₂ affected differentially the expression of superoxide dismutase (SOD) isozymes at both transcriptional and posttranscriptional levels, giving rise to a SOD activity reduction. The copper/zinc-SOD down-regulation was apparently due to the calcium (Ca) deficiency induced by the heavy metal. In these circumstances, the overproduction of the ROS hydrogen peroxide and superoxide could be observed in vivo by confocal laser microscopy, mainly associated with vascular tissue, epidermis, and mesophyll cells, and the production of superoxide radicals was prevented by exogenous Ca. On the other hand, the NO synthase-dependent NO production was strongly depressed by Cd, and treatment with Ca prevented this effect. Under these conditions, the pathogen-related proteins PrP4A and chitinase and the heat shock protein 71.2, were up-regulated, probably to protect cells against damages induced by Cd. The regulation of these proteins could be mediated by jasmonic acid and ethylene, whose contents increased by Cd treatment. A model is proposed for the cellular response to long-term Cd exposure consisting of cross talk between Ca, ROS, and NO.

Linker histone H1 is crucial for chromatin organization and gene expression in Arabidopsis thaliana , influencing development and stress responses. To explore its role in diurnal gene regulation, we examined H1-deficient plants and found that H1 is essential for maintaining rhythmic gene expression. Genes losing synchronization often contained NAC transcription factor binding sites, indicating H1 may affect their accessibility. Nuclear imaging revealed that H1 subtly modulates nuclear size and chromatin distribution across the photoperiod. Epigenetic analysis showed typical diurnal changes – declines in H3K4me3 and active RNA Pol II in the evening and increases in H3K27me3. In H1 mutants, these patterns persisted but with elevated H3K4me3 and RNA Pol II (Ser2P) levels at night and in the morning. These results suggest that H1 fine-tunes chromatin and transcriptional rhythms, contributing to the temporal coordination of gene activity in response to environmental and developmental signals.

Peroxisomes, single-membrane-bounded organelles with essentially oxidative metabolism, are key in plant responses to abiotic and biotic stresses. Recently, the presence of nitric oxide (NO) described in peroxisomes opened the possibility of new cellular functions, as NO regulates diverse biological processes by directly modifying proteins. However, this mechanism has not yet been analysed in peroxisomes. This study assessed the presence of S-nitrosylation in pea-leaf peroxisomes, purified S-nitrosylated peroxisome proteins by immunoprecipitation, and identified the purified proteins by two different mass-spectrometry techniques (matrix-assisted laser desorption/ionization tandem time-of-flight and two-dimensional nano-liquid chromatography coupled to ion-trap tandem mass spectrometry). Six peroxisomal proteins were identified as putative targets of S-nitrosylation involved in photorespiration, β-oxidation, and reactive oxygen species detoxification. The activity of three of these proteins (catalase, glycolate oxidase, and malate dehydrogenase) is inhibited by NO donors. NO metabolism/S-nitrosylation and peroxisomes were analysed under two different types of abiotic stress, i.e. cadmium and 2,4-dichlorophenoxy acetic acid (2,4-D). Both types of stress reduced NO production in pea plants, and an increase in S-nitrosylation was observed in pea extracts under 2,4-D treatment while no total changes were observed in peroxisomes. However, the S-nitrosylation levels of catalase and glycolate oxidase changed under cadmium and 2,4-D treatments, suggesting that this post-translational modification could be involved in the regulation of H₂O₂ level under abiotic stress.

Changes in natural and artificial light presumably have dramatic influences on ecological communities, yet measuring these effects can be challenging due to the difficulty in distinguishing ecological signals from background variability. Here, we used environmental DNA (eDNA) to test for light‐associated changes in a nearshore marine community. Over 8 days at Friday Harbor Laboratories, Washington, USA, we sampled seawater at midday and midnight with and without an artificial light treatment, analyzing a total of 84 samples (3 L triplicate samples) using COI and 12S markers on an Oxford Nanopore MinION platform. We detected 229 eukaryotic (COI) and 77 vertebrate (12S) taxa across 11 trophic groups, dominated by primary producers (89 species), benthic invertebrates, and fishes. Metabarcoding captured community restructuring within 30 min, such that we could observe meaningful effects of artificial light treatments at night (particularly among spawning polychaetes), as well as more fundamental community shifts in day vs. night (e.g., with primary producers, gelatinous zooplankton, and filter feeders more common during the day). These techniques offer a means of near‐real‐time assessment of wholescale changes in ecological communities, and our results here illustrate species‐ and group‐specific effects of light levels that are likely important in structuring nearshore marine communities worldwide.

Juvenile blacktip sharks ( Carcharhinus limbatus ) are highly abundant in the mangrove-fringed bays throughout the Galapagos Archipelago, utilizing these habitats as nursery grounds. Due to spatial variation in factors including temperature and larval connectivity, fish species richness is higher in the eastern portion of the archipelago. Predator diets often reflect regional prey availability, leading us to hypothesize that juvenile blacktip sharks in the eastern Galapagos would have greater prey taxa richness than those in the west. Here, we used DNA metabarcoding of fecal matter collected via non-lethal cloacal swabs to describe and quantify juvenile blacktip shark diets. We collected samples from 107 sharks across 240 km, spanning 14 bays on four islands, and released all sharks alive. The most common prey taxa identified were Thoburn’s mullet ( Mugil thoburni ; 20.0%, based on percent of occurrence), followed by fishes in the genus Abudefduf (sergeant-majors; 13.4%), Galapagos ringtail damselfish ( Stegastes beebei ; 12.7%), scalloped hammerhead shark ( Sphyrna lewini ; 11.7%), and yellowtail damselfish ( Stegastes arcifrons ; 10.7%). Prey taxa richness was highest among sharks sampled in the bays of San Cristobal, possibly due to geographic variation in prey availability. Additionally, sharks sampled during a La Niña event in 2021 had higher prey taxa richness than those sampled during an El Niño event in 2023, which could be due to El Niño-induced declines in species richness and abundance resulting from shifts in primary productivity and upwelling. A deeper understanding of shark diets can improve our ability to predict how changes in food web dynamics and prey availability affect shark populations. This knowledge is especially vital in the face of overfishing and climate change, helping to inform more effective conservation strategies and support shark survival.

During photosynthesis of higher plants, absorbed light energy is converted into chemical energy that, in part, is accumulated in the form of transitory starch within chloroplasts. In the following night, transitory starch is mobilized to sustain the heterotrophic metabolism of the plant. β-amylases are glucan hydrolases that cleave α-1,4-glycosidic bonds of starch and release maltose units from the non-reducing end of the polysaccharide chain. In Arabidopsis, nocturnal degradation of transitory starch involves mainly β-amylase-3 (BAM3). A second β-amylase isoform, β-amylase-1 (BAM1), is involved in diurnal starch degradation in guard cells, a process that sustains stomata opening. However, BAM1 also contributes to diurnal starch turnover in mesophyll cells under osmotic stress. With the aim of dissecting the role of β-amylases in osmotic stress responses in Arabidopsis, mutant plants lacking either BAM1 or BAM3 were subject to a mild (150 mM mannitol) and prolonged (up to one week) osmotic stress. We show here that leaves of osmotically-stressed bam1 plants accumulated more starch and fewer soluble sugars than both wild-type and bam3 plants during the day. Moreover, bam1 mutants were impaired in proline accumulation and suffered from stronger lipid peroxidation, compared with both wild-type and bam3 plants. Taken together, these data strongly suggest that carbon skeletons deriving from BAM1 diurnal degradation of transitory starch support the biosynthesis of proline required to face the osmotic stress. We propose the transitory-starch/proline interplay as an interesting trait to be tackled by breeding technologies aimingto improve drought tolerance in relevant crops.