Biology subjects

Metzger, S.

Publications and source records attributed to Metzger, S..

At least 19 recordsLinked to original sources

bioRxiv2026

FE DEFICIENCY-INDUCED KELCH REPEAT PROTEIN 1 (FDK1) links coumarin metabolism and iron homeostasis during alkaline iron deficiency in Arabidopsis

Although iron (Fe) is abundant in soils, its low solubility, particularly under alkaline conditions, often limits plant Fe acquisition. Under these conditions, coumarin-mediated Fe mobilization becomes increasingly important. Arabidopsis thaliana FE DEFICIENCY-INDUCED KELCH REPEAT PROTEIN 1 (FDK1, AT3G07720) is strongly induced by Fe deficiency and regulated by the central transcription factor FIT, but its function is unknown. We investigated FDK1 using genetic, physiological, metabolite, and transcriptomic analyses. Loss of FDK1 altered root growth, whereas this phenotype was restored in the FDK1-Ox overexpression line. Under alkaline Fe deficiency, growth medium from FDK1-Ox contained strongly increased levels of the Fe-mobilizing coumarins fraxetin and esculetin compared with wild type, whereas their induction was attenuated in fdk1-1. RNA-seq analysis linked FDK1 abundance to coumarin biosynthesis and iron-homeostasis gene expression. FIT and many FIT-associated genes were highly expressed in FDK1-Ox, whereas several upstream iron-homeostasis regulators, including bHLH Ib factors, were highest in fdk1-1. These findings identify FDK1 as a component of the alkaline Fe-deficiency response that promotes iron-mobilizing coumarin accumulation and is associated with coordinated regulation of iron-homeostasis genes.

plant biology↗

bioRxiv2026

Environmental drivers of heritable trait variation and lag of adaptation to climate in Hordeum murinum

1. Most plant species are genetically differentiated among populations, often reflected by phenotypic trait variation that corresponds to local adaptation. Yet the strength of local adaptation and heritable contribution to phenotypic traits vary across traits, species, and environments. Additionally, climate change is rapidly altering environmental conditions, and the climate may shift faster than populations can adapt or track the change via dispersal, resulting in adaptive lags. However, it remains unclear how widespread such adaptive lags are across plant species. 2. We focused on Hordeum murinum, an annual ruderal grass widespread in Europe. We combined continental-scale in situ measurements of 2070 plants across 207 populations with common garden experiments across two contrasting climates and two soil types to disentangle heritable variation from phenotypic plasticity and assess potential adaptive lags under climate change. 3. We found that heritable variation was pronounced in developmental traits, particularly flowering time and plant height, while seed weight, reproductive investment and SLA showed intermediate heritable contribution, and flag leaf area and total biomass were primarily plastic. Heritable trait variation was strongly associated with temperature at the populations origin, and trait clines were consistent with in situ patterns, suggesting that temperature is the main driver of genetic differentiation in H. murinum. However, we detected that fitness peaked in populations originating from warmer climates, indicating that evolutionary responses may not keep pace with rapid environmental shifts. 4. Synthesis: Our results highlight that H. murinum harbors substantial heritable variation, shaped primarily by temperature. However, the pace of evolutionary change may be insufficient to track ongoing climate change, leaving populations potentially vulnerable to future environmental conditions.

ecology↗

bioRxiv2026

Metabolic profiling and genome-scale modelling uncover mechanistic drivers of microbiome stability in synthetic maize root community

Stability is a desirable property for agricultural microbiomes, but there is a poor understanding of the mechanisms that mediate microbial community stability. A representative bacterial synthetic community from maize roots has been proposed by Niu et al. (2017, PNAS, 114:E2450) as a model system to study microbiome stability. This SynCom assembles stably when all seven members are present, but community diversity collapses without the keystone E. ludwigii strain. In this study, we used complementary in vitro experiments and in silico metabolic modelling to assess the role of metabolites for the stability of this SynCom, by defining the metabolic niches occupied by each strain, as well as their cross-feeding phenotypes and B-vitamin dependencies. We show that the individual member strains occupy complementary metabolic niches, measured by the depletion of distinct metabolites in exometabolomic experiments, as well as contrasting growth phenotypes on diverse carbon substrates, patterns which are largely recapitulated by computational simulations. Minimal medium experiments show that the established seven-member community comprises a mixture of prototrophic and auxotrophic strains. Correspondingly, experimental and in silico cross-feeding phenotypes showed that spent media harvested from the prototrophic strains can sustain growth of two auxotrophs and let to the identification of B-vitamin dependencies. Altogether, this study highlights the complementary power of in vitro and in silico approaches and suggests that the metabolic mechanisms of this SynCom can serve as design principles to inform the rational assembly of stable plant-associated microbial communities.

microbiology↗

bioRxiv2026

A hidden T-DNA-linked inversion-duplication causes a pronounced light-dependent phenotype in Arabidopsis

T-DNA insertion mutants are widely used to disrupt genes and infer their functions, yet the insertions can also trigger unintended genomic changes that confound phenotypic interpretation. Here, we used T-DNA insertion mutants affecting the major mitochondrial malate dehydrogenase (MDH1) and the heterodimeric NAD-dependent malic enzymes (ME1 and ME2) to examine their functional coordination across photoperiods and irradiance regimes. Under short days, especially at low light intensity, mdh1xme2 mutants were markedly smaller than wild type and, unexpectedly, than the mdh1xme1xme2 triple mutant, and they showed a more pronounced reduction in photosynthetic capacity. ME1 was undetectable in mdh1xme2, implying that the double and triple mutants effectively lack heterodimeric ME and should therefore behave similarly, contrary to what we observed. Whole-genome analysis resolved this discrepancy by revealing that the MDH1 T-DNA insertion in mdh1xme2 is accompanied by a major rearrangement, a 137-kbp duplication downstream of the insertion site, which was absent in the mdh1xme1xme2 triple mutant. This duplication increased gene dosage and elevated transcript abundance across the duplicated interval, while proteomics detected 5 of the 38 encoded proteins, including PEPC1. mdh1xme2 accumulated oxaloacetate-derived amino acids and displayed an altered carbon/nitrogen balance, making PEPC1 a plausible contributor to the exacerbated mdh1xme2 phenotype. Together, our data indicate that a T-DNA-linked structural variant can amplify expression of dozens of genes and intensify phenotypes at specific conditions, thereby affecting the interpretation of genotype-phenotype relationships. Because Agrobacterium-mediated DNA transfer also underpins many genome-editing workflows, our findings argue that structural validation around insertion/editing loci should be considered essential when interpreting T-DNA-derived plant lines.

plant biology↗

bioRxiv2026

Quantification of Phytohormones in Plants - Optimized Extraction, Separation and Detection

Phytohormones are key players in the regulation of plant development and metabolism. The different phytohormone classes comprise numerous chemically very diverse compounds, which are often present at very low concentrations. The chemical properties of phytohormones range from acidic to basic and from polar to non-polar. Furthermore, concentration varies strongly among different phytohormones, between plant species, tissues and developmental stages. Challenges often arise when only small amounts of plant material are available and when plant species are investigated in which the phytohormone profile has not yet been characterized. To establish a method for comprehensive phytohormone analysis we addressed these challenges by choosing and optimizing a suitable extraction method followed by optimized HPLC separation. We compared the most widely-used mass spectrometric detection methods, multiple reaction monitoring (MRM) on a triple quad instrument with high-resolution mass spectrometry (HRMS) on a Q-TOF instrument, and discuss the advantages of both methods and their limitations. O_LIWe compared various methods described in literature for the extraction of six phytohormone classes by liquid-liquid extraction and solid phase extraction purification and describe our optimizations to the selected method. C_LIO_LIWe optimized HPLC separation for 50 different phytohormones. C_LIO_LIWe evaluated the application of MRM and HRMS detection strategies. C_LI

biochemistry↗

bioRxiv2026

NADP-malic enzyme 1 couples ABA signaling to ROS-auxin patterning to restrict Arabidopsis root growth

Abscisic acid (ABA) restricts primary root growth by reshaping reactive oxygen species (ROS) dynamics and hormone signaling at the root apex, yet how cellular reductant supply for redox homeostasis is integrated into this response remains unclear. Here, we show that the cytosolic NADP-dependent malic enzyme 1 (NADP-ME1) is required for full ABA inhibition of Arabidopsis primary root elongation after germination. Three independent me1 loss-of-function mutants retained significant elongation of primary roots under ABA compared with wild type. In wild type, ABA induced an asymmetric auxin response at the root tip, whereas me1 roots failed to establish this auxin asymmetry and instead accumulated superoxide, indicating disrupted ROS balance. Pharmacological perturbation of auxin transport and ethylene biosynthesis/signaling attenuated the mutant phenotype, linking NADP-ME1 function to auxin-ethylene interactions during ABA-regulated growth. NADP-ME1 loss amplifies ABA-dependent transcriptional rewiring, including induction of oxidative stress and depression of growth-associated hormone modules. Co-immunoprecipitation coupled with bimolecular fluorescence complementation identified ascorbate peroxidase 1 (APX1) and major latex protein-like 34 (MLP34) as NADP-ME1 interaction partners, suggesting functional coupling between NADPH production and ROS detoxification. Together, our results support a model in which NADP-ME1 shapes the superoxide/H2O2 balance to control auxin patterning at the root tip and thereby execute ABA-mediated growth inhibition.

plant biology↗

bioRxiv2026

How do spotted hyaenas respond to decreased prey availability in their clan territories over the last decades?

Climate change can alter predator-prey dynamics by influencing the distribution and movements of migratory prey. Despite increasing research on predator-prey mismatches, how predators respond to changes in prey availability caused by climate change remains largely unknown, particularly for behaviourally flexible species such as central-place foragers. In the Serengeti National Park, Tanzania, increased rainfall in recent decades is thought to have altered the movement patterns of large herds of migratory herbivores, the main prey of spotted hyaenas (Crocuta crocuta) in the park, leading to a decrease in yearly migratory prey presence within hyaena clan territories. Between 1990 and 1994, migratory prey were present within hyena clan territories for about 12% of the year--mainly in May-June and November-December--dropping to just 7% between 2015 and 2019. Using longitudinal data from three Serengeti hyaena clans at the centre of the park monitored between 1990 and 2019, we investigated the impact of the observed decrease in migratory prey presence on the number of observations of hyaenas feeding at carcasses ("feeding events", n = 777), and explored associated changes in hyaena clan size. The vast majority of observed hyaena feeding events involved migratory prey species, with this relative proportion remaining constant throughout the study period. Annual patterns in the number of feeding events closely mirrored annual patterns of migratory prey presence in clan territories, with two distinct peaks mid-year and toward the end of the year. As migratory prey presence in the study clan territories declined over the years, the number of observed feeding events also decreased. However, the size of two out of three clans increased over time, suggesting that the decline in migratory prey presence in clan territories and in the number of observed feeding events did not negatively impact hyaena clans. This absence of decline in clan size may reflect the fact that hyaenas feed within their territories for only a small fraction of the year, although it also invites further investigation into the mechanisms hyaenas may employ to compensate for reduced prey availability and reduced feeding events within their clan territories.

ecology↗

bioRxiv2026

Climate-driven in-situ trait variation in an annual ruderal grass across Europe

O_LIPlant functional traits link environmental conditions to plant performance and adaptation. Growing evidence shows that in-situ intraspecific trait variation can be as important as differences between species, yet large intraspecific datasets measured in situ are rare. While most studies focused on plant morphological traits, contents of elemental nutrients in the seeds received much less attention so far. C_LIO_LIWe conducted a large-scale in-situ study of the widespread ruderal grass Hordeum murinum. We sampled 2070 individuals from 207 populations from a large part of the native range in Europe and Northern Africa. In-situ, we measured seed ripening phenology and morphological traits, and analyzed the content of elemental nutrients in the seeds. C_LIO_LIWe found that Hordeum murinum grew larger, produced seeds later, and had heavier seeds in colder and wetter areas. Plants in denser vegetation were taller with heavier seeds but formed fewer spikes. Seed nutrient content generally declined with seed weight and was mainly driven by climate. Soil conditions had only minor effects on plant traits and seed nutrients. Population identity explained much of the variation, indicating a possible genetic component. C_LIO_LISynthesis: Our findings provide a comprehensive view of Hordeum murinum responding to environmental gradients across its European distribution. Climatic variables, especially temperature, are key drivers for reproductive success and seed nutrient content, while local environments, such as biotic pressures, are more critical for growth-related traits. These patterns indicate that H. murinum modulates its growth and reproductive investment along environmental gradients, balancing phenology, stress tolerance, and limited competitive capacity. C_LI

ecology↗

bioRxiv2025

Compromised futures: gastrointestinal parasites reduce survival and recruitment but not reproductive performance in wild female spotted hyenas (Crocuta crocuta)

BackgroundGastrointestinal parasitic (GIP) infections can decrease the survival and reproductive performance of humans and livestock. Even so, the immediate and delayed fitness consequences of GIP in unmanaged wild mammal populations, particularly during the sensitive and energetically demanding early life stage, remain largely unknown. MethodsWe investigate non-invasively the effects of GIP during early life on the survival to adulthood, age at first reproduction and longevity of 68 individually known female spotted hyenas in the Serengeti National Park, Tanzania. We also test whether a high investment in gastrointestinal local immunity (i.e. faecal mucin and immunoglobulin A) and an elevated allostatic load (i.e. faecal glucocorticoid metabolites) decrease these measures of performance, when controlling for resource availability and maternal effects (i.e. maternal social rank) using logistic regression and Cox proportional hazards models. ResultsAncylostoma sp. infections and the level of immunoglobulin A both negatively associate with survival to adulthood, probably because of the damage caused by the parasite and resource allocation trade-off between immunity and maintenance. Conversely, maternal social rank has a positive influence on survival to adulthood and longevity. Immune responses, allostatic load and GIP do not affect the age at first reproduction, suggesting either no effect, a complex interaction between different life stages, or a more immediate time-dependent effect. ConclusionOur study highlights the critical role of GIP infections and maternal effects on early-life fitness and long-term outcomes in females of a wild carnivore, thereby contributing to our understanding of ecological dynamics in unmanaged ecosystems.

ecology↗

bioRxiv2025

Artificial Soil (ArtSoil): recreating soil conditions in synthetic plant growth media

Controlled plant growth in laboratories can be achieved by cultivating plants in sterile or axenic conditions on pre-defined synthetic growth media typically supplemented with sugar. In nature, plants do not receive exogenous sugar supply, form symbiosis with microbes, and plant growth is influenced by soil edaphic factors. Thus, physiological and multi-omic analyses from plants grown on synthetic media will differ from those of soil-grown plants due to the influence of sucrose, and the lack of influence from microbiota and soil edaphic factors on plant growth. The rapid advancements in spatial-omics call for accurate characterization of plants grown in conditions similar to soil. To address the issue, we developed Artificial Soil (ArtSoil), a growth medium containing essential nutrients for plant growth, and aqueous soil extract (ASE) to maintain soil microbiomes and edaphic factors, simultaneously eliminating the need for sugar supplementation in the medium. We compared Arabidopsis thaliana grown on conventional media to ArtSoil under various growth conditions, and showed that complex soil microbiota in ArtSoil promote plant growth without physiological side effects induced by sucrose. We demonstrate an application for ArtSoil in single-cell transcriptomics and report microbiota-induced cell-type specificity in immune and nitrogen signaling. We tested ArtSoil with six types of ASEs to present the potential of ArtSoil in decoupling the effects of nutrients from microbiota in plant growth. We conclude that ArtSoil recapitulates the soil environment compared to conventional media, hence, enabling physiologically relevant plant growth. Significance statementLaboratory plant growth commonly relies on sugar-supplemented media and sterile growth conditions, which introduces physiological artifacts and fails to capture the natural influences of soil microbiota and edaphic factors, leading to analyses that diverge from native conditions. We developed Artificial Soil (ArtSoil), a medium containing aqueous soil extract that supports microbiota and sugar-independent growth, and demonstrate its utility in recapitulating native soil properties and enabling physiologically relevant plant development in vitro.

plant biology↗

bioRxiv2025

Differential contributions of an antimicrobial effector from Verticillium dahliae to virulence and tomato microbiota assembly across natural soils

Throughout their life cycle plants associate with diverse and complex microbial communities, known as their microbiota. These microbiota contribute to plant performance and health, in part by providing a microbial barrier against invading plant pathogens. To colonize plant hosts, pathogens not only have to overcome host immune responses, but also breach the microbial barrier, for which they secrete so-called effector proteins. Accordingly, the soil-borne fungal plant pathogen Verticillium dahliae secretes the antimicrobial effector Ave1 to suppress antagonistic microbes and facilitate host colonization. Notably, many pathogens, including V. dahliae, have life stages outside their host plants, for instance in soil, where they encounter diverse microbial communities. Yet, how antimicrobial effectors support establishment across these environments remains poorly understood. To address this, we established a collection of natural soil samples with diverse physicochemical properties and microbiota compositions. Using this collection, we show for three plant species, barley, tomato and cotton, that root-associated bacterial and fungal communities are primarily shaped by the type of soil, whereas the phyllosphere microbiota is mainly determined by plant species. On tomato, we furthermore show that Ave1 differentially contributes to virulence on diverse soils, as Ave1 altered the tomato microbiota on all soils tested, but the taxa affected by these shifts varied depending on the specific soils. Our findings suggest that while Ave1-mediated microbiota manipulation occurs across soils, its impact on fungal virulence is influenced by the specific composition of the soil-derived microbiota assembled by the host.

plant biology↗

bioRxiv2025

SNRK3.15 is a crucial component of the sulfur deprivation response in Arabidopsis thaliana

Sulfate deprivation (-S) results in numerous metabolic and phenotypic alterations in plants. Kinases are often key players in transducing nutrient status signals to molecular components involved in metabolic and developmental program regulation, but despite the physiological importance of sulfur, to date, no signaling kinases have been identified in sulfur-deficiency signaling response programs. Here we show that the serine/threonine protein kinase CIPK14/SNRK3.15 plays a regulatory role in the -S response in Arabidopsis thaliana seedlings. Multiple molecular and physiological responses to -S are attenuated in snrk3.15 mutants, including both early adaptive responses and later emergency salvage processes including nutrient deficiency induced senescence. When grown in soil with sufficient sulfur supply, snrk3.15 mutants showed no clear phenotypes, including no difference in seed sulfur content. Lastly, the proteome dataset generated from Col-0 and snrk3.15.1 Arabidopsis seedlings under -S conditions for this project is the first of its kind and will be a valuable research resource. Proteomics data are available via ProteomeXchange with identifier PXD046612.

plant biology↗

bioRxiv2024

From Flowering Time to High Temperature Resilience: PHOTOPERIOD 1 (PPD-H1) Controls Spike Fertility through Improving Stress Resistance and Energy Metabolism under High Ambient Temperatures

High ambient temperature (HT) impairs reproductive development and grain yield in temperate crops. To ensure reproductive success under HT, plants must maintain developmental stability. However, the mechanisms integrating plant development and temperature resilience are largely unknown. Here, we demonstrate that PHOTOPERIOD 1 (PPD-H1), homologous to PSEUDO RESPONSE REGULATOR genes of the Arabidopsis circadian clock, controls developmental stability in response to HT in barley. We analyzed HT responses in independent introgression lines with either the ancestral wild-type Ppd-H1 allele or the natural ppd-h1 variant, selected in spring varieties to delay flowering and enhance yield under favourable conditions. HT delayed inflorescence development and reduced grain number in ppd-h1 mutant lines, while the wild-type Ppd-H1 genotypes accelerated reproductive development and showed a stable grain set under HT. Using a CRISPR/Cas9-induced ppd-h1 mutant, we confirmed that the CCT domain of Ppd-H1 controls developmental stability, but not clock gene expression. Transcriptome and phytohormone analyses in developing leaves and inflorescences revealed increased stress gene expression and abscisic acid levels in the leaf and inflorescence of the natural and induced mutant ppd-h1 lines. Furthermore, the mutant ppd-h1 lines downregulated photosynthesis-and energy metabolism-related genes, and reduced auxin and cytokinin levels in the inflorescence, which impaired anther and pollen development. By contrast, in the wild-type Ppd-H1 plants, the transcriptome and phytohormone levels and anther and pollen development remained stable under HT. Our findings suggest that Ppd-H1 enhances stress resistance and energy metabolism, thereby stabilizing reproductive development, floret fertility and grain set under HT.

plant biology↗

bioRxiv2024

Spotted hyena gut cross-talks:Symbionts modulate mucosal immunity

The intestinal mucosa is at the front line of host-microbiome interactions, but little is known about these interactions within natural populations. Here, we non-invasively investigated associations between the gut microbiome and mucosal immune measures while controlling for host, social, and ecological factors in 199 samples of 158 wild spotted hyenas (Crocuta crocuta) in the Serengeti National Park, Tanzania. We profiled the microbiome composition, including bacteria, fungi and parasites, using a multi-amplicon approach, and measured faecal immunoglobulin A and mucin. Probabilistic models indicated that both immune measures predict microbiome similarity among individuals in an age-dependent manner. The strength of the association effect varied, being strongest within bacteria, intermediate within parasites, and weakest within fungi communities. Machine learning regression accurately predicted both measures and identified the taxa driving these associations: symbiotic bacteria reported in humans and laboratory mice, unclassified bacteria, a hookworm, host DNA likely reflecting inflammation, and diet. Our findings indicate a complex interplay between the host, its environment and symbionts. These findings increase our knowledge of the gut microbiome in natural populations, which harbour highly dynamic and diverse eukaryotes under the influence of unpredictable environmental factors and where selection is not artificially biased.

ecology↗

bioRxiv2024

Drought resistance and improved yield result from modified malate metabolism in guard and vascular companion cells

Drought is a major threat to food security. Water loss through stomata is an inevitable consequence of CO2 uptake, and water deficit inhibits plant growth, making it challenging to develop drought-resistant strategies without compromising yield. Here, we generated tobacco plants expressing a maize NADP-dependent malate decarboxylating enzyme in stomata and vascular cells (ME plants), which show higher seed yield and faster maturation compared to wild-type (WT) plants under normal irrigation and after drought. While WT plants die after 45 days of drought, ME plants survive without any adverse effects on seed production. In addition, ME plants exhibit improved photosynthetic efficiency despite reduced stomatal conductance and changes in stem morphology, which are likely related to their ability to withstand drought. We propose that enhanced C4-like biochemistry in cells surrounding the vascular system and increased sugar export likely compensated for the reduced stomatal conductance in ME plants. The study demonstrates that cell-targeted metabolic modifications can avoid pleiotropic effects and facilitate the stacking of beneficial traits to improve crop design. Significance StatementDrought is one of the biggest threats to global food security, and its impact on crop yield is expected to worsen due to climate change. Traditionally, drought resistance has often come at the expense of yield, creating a negative trade-off. However, we present here a promising solution to this challenge. We have developed a novel approach that successfully uncouples the negative balance between drought resistance and yield. By introducing a maize enzyme into specific tobacco cells, we have created drought-resistant plants with faster growth and higher seed yield. Most importantly, after prolonged drought, while the wild type dies, the modified plants maintain their high yield. This technology paves the way for greater food security and resilience to climate change.

plant biology↗

bioRxiv2023

Apoplastic barrier establishment in roots and nodules of Lotus japonicus is essential for root-shoot signaling and N-fixation

The molecular framework underlying apoplastic root barrier formation has been unveiled in the model species Arabidopsis thaliana where establishment of Casparian strips occurs at an early stage of root development. In legumes, this region overlaps with the area where nitrogen-fixing bacteria can induce nodule formation, termed the susceptible zone. Moreover, while nodules themselves also contain an endodermis spanning their vascular bundles, it is current unknown if Casparian strips serve as a filter for transport across this specialized organ. Here we establish barrier mutants in the symbiosis model Lotus japonicus. We find that the while genetic network controlling Casparian strip formation is conserved in this legume species, formation of functional barriers is crucial for establishment of N-fixing nodules. By probing this in detail, we establish a model where the Casparian strip, via its linked Schengen pathway, converge with long distance N signaling and systemic regulation of nodulation. Moreover, this also reveal that the genetic system for barrier establishment in the root endodermis is shared in nodule vascular endodermis and required for nodule function. Combined, our findings uncover a novel role of apoplastic root barriers and establishes a mutant collection suitable to probe the role of root barriers in symbiotic plant-microbe relationships.

plant biology↗

bioRxiv2023

Hemi Manganese Exporters 1 and 2 enable manganese transport at the plasma membrane in cyanobacteria

Manganese (Mn) is key to oxygenic photosynthesis as it catalyzes the splitting of water in photosystem II and functions as cofactor of multiple enzymes. A single ABC-type transporter, MntCAB, is so far established for the uptake of the metal under limiting conditions in cyanobacteria. It is unknown how Mn is imported under replete conditions. We identified two proteins in the cyanobacterium Synechocystis sp. PCC 6803, which are homologous to the unknown protein family 0016 (UPF0016) member manganese exporter (Mnx). In contrast to Mnx, which consists of six transmembrane domains, the new candidate proteins contain three transmembrane domains. Hence, we named them hemi manganese exchangers (Hmx) 1 and 2. Knock-out mutants in hmx1 and/or hmx2 showed sensitivity toward low Mn supplementation, and reduced intracellular Mn pools. Additional deletion of mntC hindered the cells to thrive unless the medium was supplemented with Mn to compensate for the depletion of their intracellular Mn pool. In accordance with the observed localization of Hmx1 and Hmx2 in the plasma membrane, we postulate a Mn uptake function for heteromeric Hmx1/2 across the plasma membrane under a wide range of Mn concentrations and a supporting role for the MntCAB system under Mn-limiting conditions. On the basis of their phylogenies, we propose that Hmx1 and Hmx2 are the ancestral progenitors of eukaryote-type UPF0016 proteins with six transmembrane domains. The Mn transport function of Hmx1/2 underscores this as a fundamental and ancient feature of the UPF0016 family. Potentially, Hmx1 and Hmx2 coevolved with the internalization of the oxygen-evolving complex.

plant biology↗

bioRxiv2022

Explosive seed dispersal depends on SPL7 to ensure sufficient copper for localized lignin deposition via laccases

Exploding seed pods evolved in the Arabidopsis relative, Cardamine hirsuta, via morphomechanical innovations that allow the storage and rapid release of elastic energy. Asymmetric lignin deposition within endocarpb cell walls is one such innovation that is required for explosive seed dispersal and evolved in association with the trait. However, the genetic control of this novel lignin pattern is unknown. Here, we identify three lignin-polymerizing laccases, LAC4, 11 and 17, that precisely co-localize with, and are redundantly required for, asymmetric lignification of endocarpb cells. By screening for C. hirsuta mutants with less lignified fruit valves, we found that loss of function of the transcription factor gene SQUAMOSA PROMOTER BINDING PROTEIN-LIKE 7 (SPL7) caused a reduction in endocarpb cell wall lignification and a consequent reduction in seed dispersal range. SPL7 is a conserved regulator of copper homeostasis and is both necessary and sufficient for copper to accumulate in the fruit. Laccases are copper-requiring enzymes. We discovered that laccase activity in endocarpb cell walls depends on the SPL7 pathway to acclimate to copper deficiency and provide sufficient copper for lignin polymerization. Hence, SPL7 links mineral nutrition to efficient dispersal of the next generation.

plant biology↗