Forest ecosystems maintain a large share of Northern Hemisphere biodiversity. Boreal forests comprise roughly 30% of global forest area 1 and contain the highest tree density among climate zones 2 . Moreover, boreal regions are undergoing extensive climate change. Annual temperature increases exceeding 1.5 °C are projected to result in a warming of 4-11 °C by the end of this century, with little concomitant increase in precipitation 1 . At this pace, climate zones will shift northward at a greater speed than trees can migrate 3 . To understand how future populations of forest trees may respond to climate change, it is essential to uncover past and present signatures of molecular adaptation in their genomes. Silver birch, B. pendula, is a pioneer species in boreal forests of Eurasia. Flowering of the species can be artificially accelerated 4 , giving it an advantage over other tree species with published genome sequences (such as poplar 5 , spruce 6 , and pine 7 ) for the optimization of fiber and biomass production.Here we sequenced 150 birch individuals and assembled a B. pendula reference genome from a fourth-generation inbred line, resulting in a high-quality assembly of 435 Mb that was linked to chromosomes using a dense genetic map. We analyzed SNPs in the genomes of 80 birch individuals spanning most of the geographic range of B. pendula, as well as seven other members of Betulaceae. Population genomic analyses of these data provide insights into the deep-time evolution of the birch family and on recent natural selection acting on silver birch.Genome sequencing and population genomic analyses provide insights into the adaptive landscape of silver birch Silver birch (Betula pendula) is a pioneer boreal tree that can be induced to flower within 1 year. Its rapid life cycle, small (440-Mb) genome, and advanced germplasm resources make birch an attractive model for forest biotechnology. We assembled and chromosomally anchored the nuclear genome of an inbred B. pendula individual. Gene duplicates from the paleohexaploid event were enriched for transcriptional regulation, whereas tandem duplicates were overrepresented by environmental responses. Population resequencing of 80 individuals showed effective population size crashes at major points of climatic upheaval. Selective sweeps were enriched among polyploid duplicates encoding key developmental and physiological triggering functions, suggesting that local adaptation has tuned the timing of and cross-talk between fundamental plant processes. Variation around the tightlylinked light response genes PHYC and FRS10 correlated with latitude and longitude and temperature, and with precipitation for PHYC. Similar associations characterized the growth-promoting cytokinin response regulator ARR1, and the wood development genes KAK and MED5A.A full list of affiliations appears at the end of the paper.

Light is an important environmental factor that modulates acclimation strategies and defense responses in plants. We explored the functional role of the regulatory subunit B#g (B#g) of protein phosphatase 2A (PP2A) in light-dependent stress responses of Arabidopsis (Arabidopsis thaliana). The predominant form of PP2A consists of catalytic subunit C, scaffold subunit A, and highly variable regulatory subunit B, which determines the substrate specificity of PP2A holoenzymes. Mutant leaves of knockdown pp2a-b#g plants show disintegration of chloroplasts and premature yellowing conditionally under moderate light intensity. The cell-death phenotype is accompanied by the accumulation of hydrogen peroxide through a pathway that requires CONSTITUTIVE EXPRESSION OF PR GENES5 (CPR5). Moreover, the pp2a-b#g cpr5 double mutant additionally displays growth suppression and malformed trichomes. Similar to cpr5, the pp2a-b#g mutant shows constitutive activation of both salicylic acid-and jasmonic acid-dependent defense pathways. In contrast to cpr5, however, pp2a-b#g leaves do not contain increased levels of salicylic acid or jasmonic acid. Rather, the constitutive defense response associates with hypomethylation of DNA and increased levels of methionine-salvage pathway components in pp2a-b#g leaves. We suggest that the specific B#g subunit of PP2A is functionally connected to CPR5 and operates in the basal repression of defense responses under low irradiance.

Two major questions still remain to be solved: the sensory mechanism for ROS and the components involved in relaying the signals from the apoplast to the chloroplast. A comprehensive view of regulatory networks will facilitate the understanding on how environmental factors affect the production of phytonutrients and biomass in plants. Translation of such information from model plants to crop species will be at the cutting edge of research in the near future. These challenges give a frame for future studies on ROS and redox regulation of stress acclimation in photosynthetic organisms.

Biotic stress factors pose a major threat to plant health and can significantly deteriorate plant productivity by impairing the physiological functions of the plant. To combat the wide range of pathogens and insect herbivores, plants deploy converging signaling pathways, where counteracting activities of protein kinases and phosphatases form a basic mechanism for determining appropriate defensive measures. Recent studies have identified Protein Phosphatase 2A (PP2A) as a crucial component that controls pathogenesis responses in various plant species. Genetic, proteomic and metabolomic approaches have underscored the versatile nature of PP2A, which contributes to the regulation of receptor signaling, organellar signaling, gene expression, metabolic pathways, and cell death, all of which essentially impact plant immunity. Associated with this, various PP2A subunits mediate post-translational regulation of metabolic enzymes and signaling components. Here we provide an overview of protein kinase/phosphatase functions in plant immunity signaling, and position the multifaceted functions of PP2A in the tightly inter-connected regulatory network that controls the perception, signaling and responding to biotic stress agents in plants.

The evolutionary history of plants is tightly connected with the evolution of microbial pathogens and herbivores, which use photosynthetic end products as a source of life. In these interactions, plants, as the stationary party, have evolved sophisticated mechanisms to sense, signal and respond to the presence of external stress agents. Chloroplasts are metabolically versatile organelles that carry out fundamental functions in determining appropriate immune reactions in plants. Besides photosynthesis, chloroplasts host key steps in the biosynthesis of amino acids, stress hormones and secondary metabolites, which have a great impact on resistance against pathogens and insect herbivores. Changes in chloroplast redox signalling pathways and reactive oxygen species metabolism also mediate local and systemic signals, which modulate plant resistance to light stress and disease. Moreover, interplay among chloroplastic signalling networks and plasma membrane receptor kinases is emerging as a key mechanism that modulates stress responses in plants. This review highlights the central role of chloroplasts in the signalling crosstalk that essentially determines the outcome of plant-pathogen interactions in plants.

These authors contributed equally to this work. SUMMARYGlucosinolates (GSL) of cruciferous plants comprise a major group of structurally diverse secondary compounds which act as deterrents against aphids and microbial pathogens and have large commercial and ecological impacts. While the transcriptional regulation governing the biosynthesis and modification of GSL is now relatively well understood, post-translational regulatory components that specifically determine the structural variation of indole glucosinolates have not been reported. We show that the cytoplasmic protein phosphatase 2A regulatory subunit B 0 c (PP2A-B 0 c) physically interacts with indole glucosinolate methyltransferases and controls the methoxylation of indole glucosinolates and the formation of 4-methoxy-indol-3-yl-methyl glucosinolate in Arabidopsis leaves. By taking advantage of proteomic approaches and metabolic analysis we further demonstrate that PP2A-B 0 c is required to control the abundance of oligomeric protein complexes functionally linked with the activated methyl cycle and the trans-methylation capacity of leaf cells. These findings highlight the key regulatory role of PP2A-B 0 c in methionine metabolism and provide a previously unrecognized perspective for metabolic engineering of glucosinolate metabolism in cruciferous plants.

SummaryOrganellar reactive oxygen species (ROS) signalling is a key mechanism that promotes the onset of defensive measures in stress-exposed plants. The underlying molecular mechanisms and feedback regulation loops, however, still remain poorly understood. Our previous work has shown that a specific regulatory B 0 c subunit of protein phosphatase 2A (PP2A) is required to control organellar ROS signalling and associated metabolic adjustments in Arabidopsis thaliana. Here, we addressed the mechanisms through which PP2A-B 0 c impacts on organellar metabolic crosstalk and ROS homeostasis in leaves. Genetic, biochemical and pharmacological approaches, together with a combination of data-dependent acquisition (DDA) and selected reaction monitoring (SRM) MS techniques, were utilized to assess PP2A-B 0 c-dependent adjustments in Arabidopsis thaliana. We show that PP2A-B'c physically interacts with the cytoplasmic form of aconitase, a central metabolic enzyme functionally connected with mitochondrial respiration, oxidative stress responses and regulation of cell death in plants. Furthermore, PP2A-B'c impacts ROS homeostasis by controlling the abundance of specific alternative oxidase isoforms, AOX1A and AOX1D, in leaf mitochondria.We conclude that PP2A-B'c-dependent regulatory actions modulate the functional status of metabolic enzymes that essentially contribute to intracellular ROS signalling and metabolic homeostasis in plants.

Macroalgae-based products are increasing in demand also in Europe. In the European Union, each category of macroalgae-based products is regulated separately. We discuss EU legislation, including the law on medicinal products, foods including food supplements and food additives, feed and feed additives, cosmetics, packaging materials, fertilizers and biostimulants, as well as biofuels. Product safety and consumer protection are the priorities with any new products. Macroalgae products can be sold as traditional herbal medicines. The novel food regulation applies to macroalgae foods that have not previously been used as food, and organic macroalgae are a specific regulatory category. The maximum levels of heavy metals may be a barrier for macroalgae foods, feeds, and fertilizers. Getting health claims approved for foods based on macroalgae is demanding. In addition to the rules on products, the macroalgae business is strongly impacted by the elements of the general regulatory environment such as agricultural/aquacultural subsidies, maritime spatial planning and aquaculture licensing, public procurement criteria, tax schemes, and trade agreements.