Local cryptic diversity in salinity adaptation mechanisms in the wild outcrossing Brassica fruticulosa.

It is normally supposed that populations of the same species should evolve shared mechanisms of adaptation to common stressors due to evolutionary constraint. Here, we describe a system of within-species local adaptation to coastal habitats, Brassica fruticulosa, and detail surprising strategic variability in adaptive responses to high salinity. These different adaptive responses in neighboring populations are evidenced by transcriptomes, diverse physiological outputs, and distinct genomic selective landscapes. In response to high salinity Northern Catalonian populations restrict root-to-shoot Na+ transport, favoring K+ uptake. Contrastingly, Central Catalonian populations accumulate Na+ in leaves and compensate for the osmotic imbalance with compatible solutes such as proline. Despite contrasting responses, both metapopulations were salinity tolerant relative to all inland accessions. To characterize the genomic basis of these divergent adaptive strategies in an otherwise non-saline-tolerant species, we generate a long-read-based genome and population sequencing of 18 populations (nine inland, nine coastal) across the B. fruticulosa species range. Results of genomic and transcriptomic approaches support the physiological observations of distinct underlying mechanisms of adaptation to high salinity and reveal potential genetic targets of these two very recently evolved salinity adaptations. We therefore provide a model of within-species salinity adaptation and reveal cryptic variation in neighboring plant populations in the mechanisms of adaptation to an important natural stressor highly relevant to agriculture.

Signaling function of NH4+ in the activation of Fe-deficiency response in cucumber (Cucumis sativus L.).

MAIN CONCLUSION: NH4+ is necessary for full functionality of reduction-based Fe deficiency response in plants. Nitrogen (N) is present in soil mainly as nitrate (NO3-) or ammonium (NH4+). Although the significance of a balanced supply of NO3- and NH4+ for optimal growth has been generally accepted, its importance for iron (Fe) acquisition has not been sufficiently investigated. In this work, hydroponically grown cucumber (Cucumis sativus L. cv. Maximus) plants were supplied with NO3- as the sole N source under -Fe conditions. Upon the appearance of chlorosis, plants were supplemented with 2 mM NH4Cl by roots or leaves. The NH4+ treatment increased leaf SPAD and the HCl-extractable Fe concentration while decreased root apoplastic Fe. A concomitant increase in the root concentration of nitric oxide and activity of FRO and its abolishment by an ethylene action inhibitor, indicated activation of the components of Strategy I in NH4+-treated plants. Ammonium-pretreated plants showed higher utilization capacity of sparingly soluble Fe(OH)3 and higher root release of H+, phenolics, and organic acids. The expression of the master regulator of Fe deficiency response (FIT) and its downstream genes (AHA1, FRO2, and IRT1) along with EIN3 and STOP1 was increased by NH4+ application. Temporal analyses and the employment of a split-root system enabled us to suggest that a permanent presence of NH4+ at concentrations lower than 2 mM is adequate to produce an unknown signal and causes a sustained upregulation of Fe deficiency-related genes, thus augmenting the Fe-acquisition machinery. The results indicate that NH4+ appears to be a widespread and previously underappreciated component of plant reduction-based Fe deficiency response.

First Report of Shoot Blight of Grapevine Caused by Sclerotinia sclerotiorum in Illes Balears, Mallorca, Spain.

In 2021, grapevines (Vitis vinifera L.) cv. Callet growing in a commercial vineyard located at Pollença (northeast of the island of Majorca, Spain) showed severe symptoms of shoot blight during spring and early summer, with an incidence of 70%. Symptoms consisted of elongated cankered-like lesions, surrounded by water-soaked darker tissues, that developed at the base or around the middle nodes of the shoot. For fungal isolation, shoot samples with lesions were collected, surface disinfected with 2% NaCl for 90s, rinsed twice with deionized water and placed in Petri plates containing potato dextrose agar (PDA). The plates were incubated at 25°C under 12 h light-darkness for 6 days. Isolations consistently yielded on kind of fungal colonies that produced white mycelium and black spherical to elongated sclerotia (2 to 10 mm in diameter). Morphological characterization was consistent with the description of Sclerotinia sclerotiorum (Lib.) de Bary (Bolton et al. 2006). Three isolates (UIB 118-1, UIB 118-26, and UIB 129-41) were preserved and deposited in the Culture Collection of Microbiology-Faculty of Sciences, University of Balearic Islands, Spain. Genomic DNA was extracted from isolates UIB 118-26 and UIB 129-41 using the EZNA Miniprep Kit (Omega Bio-Tek, Norcross, GA). The internal transcribed spacer (ITS) region of ribosomal DNA, ß-tubulin (BTUB) and calmodulin (CAL) gene regions were amplified using ITS1F-ITS4 (Gardes and Bruns, 1996; White et al. 1990), Bt-2a/Bt-2b (Glass and Donaldson 1995) and CAL228F/CAL737R (Carbone and Kohn 1999) primer sets, respectively. Amplicons were sequenced and deposited in GenBank with accession numbers MZ604647 and MZ604648 for ITS, OK634402 and OK634403 for BTUB and OK634404 and OK634405 for CAL. BLASTn search showed that isolates were >99 % (ITS, BTUB and CAL) identical to S. sclerotiorum GenBank accession no. KF859933, CP017815 and KF871381, respectively. Pathogenicity tests were conducted using eight one-year old grapevines cv. Cabernet Sauvignon. Old and new green shoots were inoculated by inserting a 6-mm plug of mycelium taken from actively growing cultures on PDA into cuts made at the base and at the distal part of each shoot with a sterile scalpel with a total of eight inoculation points per plant. Inoculated wounds were sealed with Parafilm tape to avoid rapid dehydration. Inoculated plants and an equal number of wounded but non-inoculated plants (negative controls) were maintained at 25 ± 1°C for 48 h in plastic containers to ensure a high relative humidity (>90%). After 5 days, the infection girdled and rotted the green new shoots, whereas the older partially lignified shoots developed a localized long brown lesion that reached 16 cm in length. Due to the rotting of the basal part of the petiole, leaves turned gray, wilted, and died, easily detaching from the stem. In advanced stages of the disease, 7 days after infection, branches died and fell with the leaves remained attached (Fig 1 A, B). Reisolations from diseased shoots were successfully performed on PDA to fulfill Koch's postulates. S. slerotiorum was previously reported on grapevine causing shoot blight in Chile (Latorre and Guerrero, 2001), Korea (Jong-Han et al. 2009), California-USA (Boland and Hall, 1994) and Australia (Hall et al. 2002). AlsoS. sclerotiorum was reported among the endophytic mycobiota associated with Vitis vinifera in the Iberian Peninsula (Gonzalez and Tello, 2011) but not as a pathogen causing visible symptoms on that crop. So, this is the first report of the occurrence of S. slerotiorum as a pathogen of grapevines in Spain causing symptoms of canker and shoot blight. This finding highlights a potential risk of this fungal disease for the wine industry in the Mediterranean region and specially for Spain, the country with the largest acreage devoted to grapevines. Although chemical and biological are suitable control strategies, disease management is difficult as sclerotia of Sclerotinia can remain in the soil for up to eight years (Adams and Ayears, 1979), and preventive surveys are greatly recommended as an important epidemiological tool to monitor the epidemiology of disease and identify potential outbreaks of this new pathogen on grapevine in Spain.

The unseen world beneath our feet: Heliyon soil science. Exploring the cutting-edge techniques and ambitious goals of modern soil science.

In the face of climate change, ecosystem destruction, desertification, and increasing food demand, soil conservation is crucial for ensuring the sustainability of life on Earth. The Soil Section of Heliyon aims to be a platform for basic and applied soil science research, emphasizing the central role of soils and their interactions with human activities. This editorial highlights recent research trends in soil science, including the evolving definition of soil, the multifunctionality of soils and their biodiversity, soil degradation and erosion, the role of soil microflora, advancements in soil mapping techniques, global change and the carbon cycle, soil health, the relationship between soil and buildings, and the importance of considering soil quality in land use planning and policies. The Heliyon Soil Science section seeks to publish scientifically accurate and valuable research that explores the diverse functions of soil and their significance in sustainable land-use systems.

Combined genomics to discover genes associated with tolerance to soil carbonate.

Carbonate-rich soils limit plant performance and crop production. Previously, local adaptation to carbonated soils was detected in wild Arabidopsis thaliana accessions, allowing the selection of two demes with contrasting phenotypes: A1 (carbonate tolerant, c+) and T6 (carbonate sensitive, c-). Here, A1(c+) and T6(c - ) seedlings were grown hydroponically under control (pH 5.9) and bicarbonate conditions (10 mM NaHCO3 , pH 8.3) to obtain ionomic profiles and conduct transcriptomic analysis. In parallel, A1(c+) and T6(c - ) parental lines and their progeny were cultivated on carbonated soil to evaluate fitness and segregation patterns. To understand the genetic architecture beyond the contrasted phenotypes, a bulk segregant analysis sequencing (BSA-Seq) was performed. Transcriptomics revealed 208 root and 2503 leaf differentially expressed genes in A1(c+) versus T6(c - ) comparison under bicarbonate stress, mainly involved in iron, nitrogen and carbon metabolism, hormones and glycosylates biosynthesis. Based on A1(c+) and T6(c - ) genome contrasts and BSA-Seq analysis, 69 genes were associated with carbonate tolerance. Comparative analysis of genomics and transcriptomics discovered a final set of 18 genes involved in bicarbonate stress responses that may have relevant roles in soil carbonate tolerance.

Weed Species from Tea Gardens as a Source of Novel Aluminum Hyperaccumulators.

Increased availability of toxic Al3+ is the main constraint limiting plant growth on acid soils. Plants adapted to acid soils, however, tolerate toxic Al3+, and some can accumulate Al in their aerial parts to a significant degree. Studies on Al-tolerant and Al-accumulating species have mainly focused on the vegetation of acid soils distributed as two global belts in the northern and southern hemispheres, while acid soils formed outside these regions have been largely neglected. The acid soils (pH 3.4-4.2) of the tea plantations in the south Caspian region of Northern Iran were surveyed over three seasons at two main locations. Aluminum and other mineral elements (including nutrients) were measured in 499 plant specimens representing 86 species from 43 families. Al accumulation exceeding the criterion for accumulator species (>1000 µg g-1 DW) was found in 36 species belonging to 23 families of herbaceous annual or perennial angiosperms, in addition to three bryophyte species. Besides Al, Fe accumulation (1026-5155 µg g-1 DW) was also observed in the accumulator species that exceeded the critical toxicity concentration, whereas no such accumulation was observed for Mn. The majority of analyzed accumulator plants (64%) were cosmopolitan or pluriregional species, with a considerable rate of Euro-Siberian elements (37%). Our findings, which may contribute to phylogenetic studies of Al accumulators, also suggest suitable accumulator and excluder species for the rehabilitation of acid-eroded soils and introduce new model species for investigating Al accumulation and exclusion mechanisms.

A genome-wide association study identifies novel players in Na and Fe homeostasis in Arabidopsis thaliana under alkaline-salinity stress.

In nature, multiple stress factors occur simultaneously. The screening of natural diversity panels and subsequent Genome-Wide Association Studies (GWAS) is a powerful approach to identify genetic components of various stress responses. Here, the nutritional status variation of a set of 270 natural accessions of Arabidopsis thaliana grown on a natural saline-carbonated soil is evaluated. We report significant natural variation on leaf Na (LNa) and Fe (LFe) concentrations in the studied accessions. Allelic variation in the NINJA and YUC8 genes is associated with LNa diversity, and variation in the ALA3 is associated with LFe diversity. The allelic variation detected in these three genes leads to changes in their mRNA expression and correlates with plant differential growth performance when plants are exposed to alkaline salinity treatment under hydroponic conditions. We propose that YUC8 and NINJA expression patters regulate auxin and jasmonic signaling pathways affecting plant tolerance to alkaline salinity. Finally, we describe an impairment in growth and leaf Fe acquisition associated with differences in root expression of ALA3, encoding a phospholipid translocase active in plasma membrane and the trans Golgi network which directly interacts with proteins essential for the trafficking of PIN auxin transporters, reinforcing the role of phytohormonal processes in regulating ion homeostasis under alkaline salinity.

Genome-Wide Association Study Reveals Key Genes for Differential Lead Accumulation and Tolerance in Natural Arabidopsis thaliana Accessions.

Soil contamination by lead (Pb) has become one of the major ecological threats to the environment. Understanding the mechanisms of Pb transport and deposition in plants is of great importance to achieve a global Pb reduction. We exposed a collection of 360 Arabidopsis thaliana natural accessions to a Pb-polluted soil. Germination rates, growth, and leaf Pb concentrations showed extensive variation among accessions. These phenotypic data were subjected to genome wide association studies (GWAs) and we found a significant association on chromosome 1 for low leaf Pb accumulation. Genes associated with significant SNP markers were evaluated and we selected EXTENSIN18 (EXT18) and TLC (TRAM-LAG1-CLN8) as candidates for having a role in Pb homeostasis. Six Pb-tolerant accessions, three of them exhibiting low leaf Pb content, and three of them with high leaf Pb content; two Pb-sensitive accessions; two knockout T-DNA lines of GWAs candidate genes (ext18, tlc); and Col-0 were screened under control and high-Pb conditions. The relative expression of EXT18, TLC, and other genes described for being involved in Pb tolerance was also evaluated. Analysis of Darwinian fitness, root and leaf ionome, and TEM images revealed that Pb-tolerant accessions employ two opposing strategies: (1) low translocation of Pb and its accumulation into root cell walls and vacuoles, or (2) high translocation of Pb and its efflux to inactive organelles or intracellular spaces. Plants using the first strategy exhibited higher expression of EXT18 and HMA3, thicker root cell walls and Pb vacuolar sequestration, suggesting that these genes may contribute to the deposition of Pb in the roots. On the other hand, plants translocating high amounts of Pb showed upregulation of TLC and ABC transporters, indicating that these plants were able to properly efflux Pb in the aerial tissues. We conclude that EXT18 and TLC upregulation enhances Pb tolerance promoting its sequestration: EXT18 favors the thickening of the cell walls improving Pb accumulation in roots and decreasing its toxicity, while TLC facilitates the formation of dictyosome vesicles and the Pb encapsulation in leaves. These findings are relevant for the design of phytoremediation strategies and environment restoration.

Adaptation to coastal soils through pleiotropic boosting of ion and stress hormone concentrations in wild Arabidopsis thaliana.

Local adaptation in coastal areas is driven chiefly by tolerance to salinity stress. To survive high salinity, plants have evolved mechanisms to specifically tolerate sodium. However, the pathways that mediate adaptive changes in these conditions reach well beyond Na+ . Here we perform a high-resolution genetic, ionomic, and functional study of the natural variation in Molybdenum transporter 1 (MOT1) associated with coastal Arabidopsis thaliana accessions. We quantify the fitness benefits of a specific deletion-harbouring allele (MOT1DEL ) present in coastal habitats that is associated with lower transcript expression and molybdenum accumulation. Analysis of the leaf ionome revealed that MOT1DEL plants accumulate more copper (Cu) and less sodium (Na+ ) than plants with the noncoastal MOT1 allele, revealing a complex interdependence in homeostasis of these three elements. Our results indicate that under salinity stress, reduced MOT1 function limits leaf Na+ accumulation through abscisic acid (ABA) signalling. Enhanced ABA biosynthesis requires Cu. This demand is met in Cu deficient coastal soils through MOT1DEL increasing the expression of SPL7 and the copper transport protein COPT6. MOT1DEL is able to deliver a pleiotropic suite of phenotypes that enhance salinity tolerance in coastal soils deficient in Cu. This is achieved by inducing ABA biosynthesis and promoting reduced uptake or better compartmentalization of Na+ , leading to coastal adaptation.

Identifying the Specific Root Microbiome of the Hyperaccumulator Noccaea brachypetala Growing in Non-metalliferous Soils.

Noccaea brachypetala is a close relative of Noccaea caerulescens, a model plant species used in metal hyperaccumulation studies. In a previous survey in the Catalan Pyrenees, we found two occidental and two oriental N. brachypetala populations growing on non-metalliferous soils, with accumulated high concentrations of Cd and Zn. Our hypothesis was that the microbiome companion of the plant roots may influence the ability of these plants to absorb metals. We performed high-throughput sequencing of the bacterial and fungal communities in the rhizosphere soil and rhizoplane fractions. The rhizobiomes and shoot ionomes of N. brachypetala plants were analyzed along with those from other non-hyperaccumulator Brassicaceae species found at the same sampling locations. The analyses revealed that microbiome richness and relative abundance tended to increase in N. brachypetala plants compared to non-hyperaccumulator species, regardless of plant location. We confirmed that the root compartment is a key factor in describing the community composition linked to the cohabiting Brassicaceae species, and the rhizoplane fraction contained the specific and rare taxa associated with each species. N. brachypetala plants harbored a similar relative abundance of fungi compared to the other plant hosts, but there was a notable reduction in some specific taxa. Additionally, we observed an enrichment in the hyperaccumulator rhizoplane of previously described metal-tolerant bacteria and bacteria involved in nitrogen cycling. The bacteria involved in the nitrogen cycle could contribute indirectly to the hyperaccumulator phenotype by improving soil quality and fertility. Our results indicate that N. brachypetala captures a particular prokaryotic community from the soil. This particular prokaryotic community may benefit the extraction of metal ions and/or improve plant nutrition. Our research identified satellite groups associated with the root niche of a hyperaccumulator plant that may assist in improving biological strategies in heavy metal remediation.

Luxury zinc supply acts as antiaging agent and enhances reproductive fitness in Arabidopsis thaliana.

Developmental senescence in plants is an age dependent process affected by phytohormones, nutrient status, and environmental factors, while the antiaging effects of zinc are recognized in humans. This study explores the possible influence of a high, non-toxic Zn-supply (12 µM) on senescence and reproductive fitness in A. thaliana. Auxin-resistance mutant, axr1-12, and auxin overexpressing YUCCA6 mutant, yuc6-1D, and their corresponding background genotypes were grown until complete rosette senescence to quantify the fruit biomass and seed number. Gene expression of different antioxidant, auxin and senescence-associated markers were analyzed after the onset of senescence. All mutants showed delayed developmental senescence. Luxury Zn delayed senescence in wild type, but not in the mutant genotypes. Excluding axr1-12 mutants, which showed very low expression of the auxin gene marker INDOLE-3-ACETIC ACID INDUCIBLE 2 (IAA2), enhanced expression of the senescence markers SENESCENCE-ASSOCIATED GENE 12 (SAG12) and AUXIN RESPONSE FACTOR 2 (ARF2) coincided with decreased expression of IAA2. Delayed senescence and total number of seeds per plant were related to higher expression of the peroxisomal antioxidant enzymes Cu/Zn superoxide dismutase (SOD3) and catalase (CAT2). These results evidence that high Zn-induced delayed senescence and improved reproductive fitness in Arabidopsis are related to an auxin-independent mechanism that retains antioxidant activity.

Transcriptomics Reveals Fast Changes in Salicylate and Jasmonate Signaling Pathways in Shoots of Carbonate-Tolerant Arabidopsis thaliana under Bicarbonate Exposure.

High bicarbonate concentrations of calcareous soils with high pH can affect crop performance due to different constraints. Among these, Fe deficiency has mostly been studied. The ability to mobilize sparingly soluble Fe is a key factor for tolerance. Here, a comparative transcriptomic analysis was performed with two naturally selected Arabidopsis thaliana demes, the carbonate-tolerant A1(c+) and the sensitive T6(c-). Analyses of plants exposed to either pH stress alone (pH 5.9 vs. pH 8.3) or to alkalinity caused by 10 mM NaHCO3 (pH 8.3) confirmed better growth and nutrient homeostasis of A1(c+) under alkaline conditions. RNA-sequencing (RNA-seq) revealed that bicarbonate quickly (3 h) induced Fe deficiency-related genes in T6(c-) leaves. Contrastingly, in A1(c+), initial changes concerned receptor-like proteins (RLP), jasmonate (JA) and salicylate (SA) pathways, methionine-derived glucosinolates (GS), sulfur starvation, starch degradation, and cell cycle. Our results suggest that leaves of carbonate-tolerant plants do not sense iron deficiency as fast as sensitive ones. This is in line with a more efficient Fe translocation to aerial parts. In A1(c+) leaves, the activation of other genes related to stress perception, signal transduction, GS, sulfur acquisition, and cell cycle precedes the induction of iron homeostasis mechanisms yielding an efficient response to bicarbonate stress.

The arbuscular mycorrhizal mycelium from barley differentially influences various defense parameters in the non-host sugar beet under co-cultivation.

The interactions between arbuscular mycorrhizal fungi (AMF) and non-host species are poorly studied. Particularly scarce is information on members of the Amaranthaceae/Chenopodiaceae family. Sugar beet (Beta vulgaris) plants were co-cultivated with a host species (Hordeum vulgare) in the presence (+AMF) or absence of Rhizophagus intraradices to explore the hypothesis that the presence of an active, pre-established AMF mycelium induces defense responses in the non-host species. Biomass of sugar beet did not respond to the +AMF treatment, while its root exudation of organic acids and phenolic acids was drastically decreased upon co-cultivation with +AMF barley. The most conspicuous effect was observed on a wide range of potential defense parameters being differentially influenced by the +AMF treatment in this non-host species. Antioxidant defense enzymes were activated and the level of endogenous jasmonic acid was elevated accompanied by nitric oxide accumulation and lignin deposition in the roots after long-term +AMF treatment. In contrast, significant reductions in the levels of endogenous salicylic acid and tissue concentration and exudation of phenolic acids indicated that AM fungus hyphae in the substrate did not induce a hypersensitive-type response in the sugar beet roots and downregulated certain chemical defenses. Our results imply that the fitness of this non-host species is not reduced when grown in the presence of an AMF mycelium because of balanced defense costs. Further studies should address the question of whether or not such modulation of defense pattern influences the pest resistance of sugar beet plants under field conditions.

Contrasting allocation of magnesium, calcium and manganese in leaves of tea (Camellia sinensis (L.) Kuntze) plants may explain their different extraction efficiency into tea.

During tea preparation mineral elements are extracted from the dried leaves of tea (Camellia sinensis (L.) Kuntze) plants into the solution. Micro-particle induced X-ray emission was employed to investigate the spatial distribution of magnesium (Mg), calcium (Ca) and manganese (Mn) in the young and old leaves of tea plants grown in the absence and presence of aluminium (Al) in the substrate. Results revealed that in tea leaves the largest concentrations of Mg occurred in the epidermis, of Ca in oxalate crystals and of Mn in epidermis and oxalate crystals; there was a leaf-age effect on tissue-specific concentrations of Mg, Ca and Mn with all tissues of old leaves containing larger concentrations of Mg, Ca and Mn than young leaves; supplementation of substrate with Al reduced concentrations of Mg, Ca and Mn in the old leaves, and a link between the distribution of Mg, Ca and Mn in the tea leaves with the extraction efficiencies of these elements into the tea was possible. We conclude that old leaves of tea plants cultivated under conditions of low Al availability will have the largest concentrations of Mg, Ca and Mn and may represent most acceptable ingredient for the preparation of tea.

Aluminium alters mineral composition and polyphenol metabolism in leaves of tea plants (Camellia sinensis).

Tea plants (Camellia sinensis) can hyperaccumulate and tolerate high leaf concentrations of aluminium (Al). The quality of tealeaves and the positive health effects of their infusion depend on the leaf concentrations of both polyphenolic substances and mineral elements. This study explored the influence of Al supply on these leaf components under low and optimal phosphorus (P) availability. After 8 weeks exposure in hydroponics, multifactorial analysis revealed a negative influence of leaf Al on magnesium (Mg), P, boron (B), and manganese (Mn) leaf concentrations. Contrastingly, these essential mineral nutrients were positively related to leaf epigallocatechin. Galloylated catechins were positively related to leaf iron (Fe). After short-term exposure (24 and 96 h), RT-qPCR (Reverse Transcription-quantitative Polymerase Chain Reaction) analysis revealed upregulation of galloylation-related genes by substrate acidification both in old and young leaves. Only the extremely high Al accumulation in old leaves activated genes involved in biosynthesis of galloylated catechins, while in young leaves the lower Al leaf concentrations activated genes involved in anthocyanin accumulation. In conclusion, low pH and enhanced Al availability to tea plants have a strong influence on the polyphenolic pattern of tealeaves and therefore may alter both the leaves' antioxidant properties and their ability to bind Al and Fe in non-toxic form.

A Role for Zinc in Plant Defense Against Pathogens and Herbivores.

Pests and diseases pose a threat to food security, which is nowadays aggravated by climate change and globalization. In this context, agricultural policies demand innovative approaches to more effectively manage resources and overcome the ecological issues raised by intensive farming. Optimization of plant mineral nutrition is a sustainable approach to ameliorate crop health and yield. Zinc is a micronutrient essential for all living organisms with a key role in growth, development, and defense. Competition for Zn affects the outcome of the host-attacker interaction in both plant and animal systems. In this review, we provide a clear framework of the different strategies involving low and high Zn concentrations launched by plants to fight their enemies. After briefly introducing the most relevant macro- and micronutrients for plant defense, the functions of Zn in plant protection are summarized with special emphasis on superoxide dismutases (SODs) and zinc finger proteins. Following, we cover recent meaningful studies identifying Zn-related passive and active mechanisms for plant protection. Finally, Zn-based strategies evolved by pathogens and pests to counteract plant defenses are discussed.

How Plants Handle Trivalent (+3) Elements.

Plant development and fitness largely depend on the adequate availability of mineral elements in the soil. Most essential nutrients are available and can be membrane transported either as mono or divalent cations or as mono- or divalent anions. Trivalent cations are highly toxic to membranes, and plants have evolved different mechanisms to handle +3 elements in a safe way. The essential functional role of a few metal ions, with the possibility to gain a trivalent state, mainly resides in the ion's redox activity; examples are iron (Fe) and manganese. Among the required nutrients, the only element with +3 as a unique oxidation state is the non-metal, boron. However, plants also can take up non-essential trivalent elements that occur in biologically relevant concentrations in soils. Examples are, among others, aluminum (Al), chromium (Cr), arsenic (As), and antimony (Sb). Plants have evolved different mechanisms to take up and tolerate these potentially toxic elements. This review considers recent studies describing the transporters, and specific and unspecific channels in different cell compartments and tissues, thereby providing a global vision of trivalent element homeostasis in plants.

Soil carbonate drives local adaptation in Arabidopsis thaliana.

High soil carbonate limits crop performance especially in semiarid or arid climates. To understand how plants adapt to such soils, we explored natural variation in tolerance to soil carbonate in small local populations (demes) of Arabidopsis thaliana growing on soils differing in carbonate content. Reciprocal field-based transplants on soils with elevated carbonate (+C) and without carbonate (-C) over several years revealed that demes native to (+C) soils showed higher fitness than those native to (-C) soils when both were grown together on carbonate-rich soil. This supports the role of soil carbonate as a driving factor for local adaptation. Analyses of contrasting demes revealed key mechanisms associated with these fitness differences. Under controlled conditions, plants from the tolerant deme A1(+C) native to (+C) soil were more resistant to both elevated carbonate and iron deficiency than plants from the sensitive T6(-C) deme native to (-C) soil. Resistance of A1(+C) to elevated carbonate was associated with higher root extrusion of both protons and coumarin-type phenolics. Tolerant A1(+C) also had better Ca-exclusion than sensitive T6(-C) . We conclude that Arabidopsis demes are locally adapted in their native habitat to soils with moderately elevated carbonate. This adaptation is associated with both enhanced iron acquisition and calcium exclusion.

Snails prefer it sweet: A multifactorial test of the metal defence hypothesis.

Metal defence against insect herbivory in hyperaccumulator plants is well documented. However, there are contradictory results regarding protection against snails. According to the joint effects hypothesis, inorganic and organic defences cooperate in plant protection. To test this hypothesis, we explored the relationships between snail (Cantareus aspersus) feeding and multiple inorganic and organic leaf components in the Cd hyperaccumulator plant Noccaea praecox. Plants grouped by rosette size growing in nutrient solution supplemented or not with 50 µM Cd were offered to the snails. After 3 days of snail feeding, the plants and snails were analysed. In addition to Cd concentrations, we analysed leaves for nutritional factors (sugar and protein), defence-related compounds (glucosinolates, phenolics, tannins, salicylic acid and jasmonate) and essential mineral nutrients. Cadmium concentrations in the snails and in snail excrements were also analysed. Snails preferentially fed on plants grown without Cd. Medium-sized plants exposed to Cd were the least consumed. Snail excrements from this trial weighed less and had higher Cd concentrations than those from other treatments. Cadmium increased salicylate and jasmonate production. A positive relationship between jasmonate levels and the number of attacked leaves was found. Principal component analysis revealed that leaf sugar concentration was the main factor positively affecting snails' leaf consumption, while leaf Cd had a negative but weaker influence. In conclusion, leaf sugar concentration mainly governs snails' feeding preferences. High leaf Cd concentrations do not deter herbivores from attacking leaves, but they do reduce leaf consumption. Our results clearly support the joint effects hypothesis.

Fluctuating selection on migrant adaptive sodium transporter alleles in coastal Arabidopsis thaliana.

Stressors such as soil salinity and dehydration are major constraints on plant growth, causing worldwide crop losses. Compounding these insults, increasing climate volatility requires adaptation to fluctuating conditions. Salinity stress responses are relatively well understood in Arabidopsis thaliana, making this system suited for the rapid molecular dissection of evolutionary mechanisms. In a large-scale genomic analysis of Catalonian A. thaliana, we resequenced 77 individuals from multiple salinity gradients along the coast and integrated these data with 1,135 worldwide A. thaliana genomes for a detailed understanding of the demographic and evolutionary dynamics of naturally evolved salinity tolerance. This revealed that Catalonian varieties adapted to highly fluctuating soil salinity are not Iberian relicts but instead have immigrated to this region more recently. De novo genome assembly of three allelic variants of the high-affinity K+ transporter (HKT1;1) locus resolved structural variation between functionally distinct alleles undergoing fluctuating selection in response to seasonal changes in soil salinity. Plants harboring alleles responsible for low root expression of HKT1;1 and consequently high leaf sodium (HKT1;1HLS ) were migrants that have moved specifically into areas where soil sodium levels fluctuate widely due to geography and rainfall variation. We demonstrate that the proportion of plants harboring HKT1;1HLS alleles correlates with soil sodium level over time, HKT1;1HLS -harboring plants are better adapted to intermediate levels of salinity, and the HKT1;1HLS allele clusters with high-sodium accumulator accessions worldwide. Together, our evidence suggests that HKT1;1 is under fluctuating selection in response to climate volatility and is a worldwide determinant in adaptation to saline conditions.