Stomatal CO2/bicarbonate sensor consists of two interacting protein kinases, Raf-like HT1 and nonkinase-activity activity requiring MPK12/MPK4

Publisher Copyright: © 2022 The Authors.The continuing rise in the atmospheric carbon dioxide (CO2) concentration causes stomatal closing, thus critically affecting transpirational water loss, photosynthesis, and plant growth. However, the primary CO2 sensor remains unknown. Here, we show that elevated CO2 triggers interaction of the MAP kinases MPK4/MPK12 with the HT1 protein kinase, thus inhibiting HT1 kinase activity. At low CO2, HT1 phosphorylates and activates the downstream negatively regulating CBC1 kinase. Physiologically relevant HT1-mediated phosphorylation sites in CBC1 are identified. In a genetic screen, we identify dominant active HT1 mutants that cause insensitivity to elevated CO2. Dominant HT1 mutants abrogate the CO2/bicarbonate-induced MPK4/12-HT1 interaction and HT1 inhibition, which may be explained by a structural AlphaFold2- and Gaussian-accelerated dynamics-generated model. Unexpectedly, MAP kinase activity is not required for CO2 sensor function and CO2-triggered HT1 inhibition and stomatal closing. The presented findings reveal that MPK4/12 and HT1 together constitute the long-sought primary stomatal CO2/bicarbonate sensor upstream of the CBC1 kinase in plants.Peer reviewe

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 tightly-linked 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.Peer reviewe

Author Correction: Genome sequencing and population genomic analyses provide insights into the adaptive landscape of silver birch.

In the version of this article initially published, there was a mistake in the calculation of the nucleotide mutation rate per site per generation: 1 × 10−9 mutations per site per generation was used, whereas 9.5 × 10−9 was correct. This error affects the interpretation of population-size changes over time and their possible correspondence with known geological events, as shown in the original Fig. 4 and supporting discussion in the text, as well as details in the Supplementary Note. Neither the data themselves nor any other results are affected. Figure 4 has been revised accordingly. Images of the original and corrected figure panels are shown in the correction notice

Characterisation of the GAAP (Golgi anti-apoptotic protein) gene family in Arabidopsis thaliana

Programmed cell death (PCD) plays an essential role in eukaryotes during growth and development and in response to stress signals. GAAPs (Golgi anti-apoptotic protein) are a novel, evolutionarily conserved group of anti-apoptotic proteins. Human and viral GAAPs have been shown to inhibit apoptosis and modulate intracellular calcium fluxes. There is an apparent expansion of the GAAP gene family in plants, with five paralogous genes present in the Arabidopsis thaliana genome (AtGAAP1-5). AtGAAPs share the UPF0005 signature motif with animal and plant proteins that have been shown to function as inhibitors of cell death, including Bax inhibitor-1 and Lifeguard. AtGAAP genes show distinct expression patterns with AtGAAP4 and AtGAAP2 showing the highest overall transcript abundance based on publicly available microarray data and RT-PCR analysis. AtGAAP gene expression analysis using promoter-GUS fusions revealed overlapping expression patterns for AtGAAP1, AtGAAP2 and AtGAAP4 in floral organs, with AtGAAP2 and AtGAAP4 also highly expressed in leaf tissue. AtGAAP5 however showed floral-specific expression that was mostly distinct from the expression pattern of AtGAAP1, AtGAAP2 and AtGAAP4 in the flowers. AtGAAP3 expression was undetectable by GUS staining. Intracellular localisation of fluorescent protein-tagged AtGAAPs was studied using stable or transient expression in Arabidopsis and Nicotiana benthamiana, respectively. All AtGAAPs were confirmed to localise to the Golgi at low expression levels and AtGAAP1 and AtGAAP2 additionally localised to the tonoplast at higher expression levels. Analysis of single knock-out mutants of AtGAAPs revealed no obvious developmental or PCD-related phenotypes. Measurement of cytosolic Ca2+ rises following H2O2 or mannitol treatment in atgaap null mutants, transgenically expressing proaequorin, indicated a potential role for AtGAAPs in Ca2+ signalling, however, these data are preliminary. Several double and triple atgaap mutants have been generated, all of which display a wild-type growth habit suggesting either redundancy within the AtGAAP gene family or the existence of a subtle phenotype that is not apparent under the conditions used. Phenotypes have however been uncovered in plants overexpressing AtGAAP-YFP fusion proteins. AtGAAP1 overexpressors display a slight dwarf phenotype whereas AtGAAP2 overexpressors show severely twisted branches. AtGAAP5 overexpressors display a severe dwarf phenotype, enhanced senescence and development of spontaneous lesions in both rosette and cauline leaves. Moderate to high expression of AtGAAP5 presumably leads to lethality, as no transgenic plants that express AtGAAP5-YFP at these levels have been recovered

Characterisation of the GAAP (Golgi anti-apoptotic protein) gene family in Arabidopsis thaliana

Programmed cell death (PCD) plays an essential role in eukaryotes during growth and development and in response to stress signals. GAAPs (Golgi anti-apoptotic protein) are a novel, evolutionarily conserved group of anti-apoptotic proteins. Human and viral GAAPs have been shown to inhibit apoptosis and modulate intracellular calcium fluxes. There is an apparent expansion of the GAAP gene family in plants, with five paralogous genes present in the Arabidopsis thaliana genome (AtGAAP1-5). AtGAAPs share the UPF0005 signature motif with animal and plant proteins that have been shown to function as inhibitors of cell death, including Bax inhibitor-1 and Lifeguard. AtGAAP genes show distinct expression patterns with AtGAAP4 and AtGAAP2 showing the highest overall transcript abundance based on publicly available microarray data and RT-PCR analysis. AtGAAP gene expression analysis using promoter-GUS fusions revealed overlapping expression patterns for AtGAAP1, AtGAAP2 and AtGAAP4 in floral organs, with AtGAAP2 and AtGAAP4 also highly expressed in leaf tissue. AtGAAP5 however showed floral-specific expression that was mostly distinct from the expression pattern of AtGAAP1, AtGAAP2 and AtGAAP4 in the flowers. AtGAAP3 expression was undetectable by GUS staining. Intracellular localisation of fluorescent protein-tagged AtGAAPs was studied using stable or transient expression in Arabidopsis and Nicotiana benthamiana, respectively. All AtGAAPs were confirmed to localise to the Golgi at low expression levels and AtGAAP1 and AtGAAP2 additionally localised to the tonoplast at higher expression levels. Analysis of single knock-out mutants of AtGAAPs revealed no obvious developmental or PCD-related phenotypes. Measurement of cytosolic Ca2+ rises following H2O2 or mannitol treatment in atgaap null mutants, transgenically expressing proaequorin, indicated a potential role for AtGAAPs in Ca2+ signalling, however, these data are preliminary. Several double and triple atgaap mutants have been generated, all of which display a wild-type growth habit suggesting either redundancy within the AtGAAP gene family or the existence of a subtle phenotype that is not apparent under the conditions used. Phenotypes have however been uncovered in plants overexpressing AtGAAP-YFP fusion proteins. AtGAAP1 overexpressors display a slight dwarf phenotype whereas AtGAAP2 overexpressors show severely twisted branches. AtGAAP5 overexpressors display a severe dwarf phenotype, enhanced senescence and development of spontaneous lesions in both rosette and cauline leaves. Moderate to high expression of AtGAAP5 presumably leads to lethality, as no transgenic plants that express AtGAAP5-YFP at these levels have been recovered.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Synthesis and import of GDP-l-fucose into the Golgi affect plant-water relations.

Publication status: PublishedFunder: Ella ja Georg Ehrnroothin Säätiö; doi: http://dx.doi.org/10.13039/501100003502Funder: European Regional Development Fund; doi: http://dx.doi.org/10.13039/501100008530Funder: Helsingin Yliopisto; doi: http://dx.doi.org/10.13039/100007797Funder: Opetushallitus; doi: http://dx.doi.org/10.13039/501100011842Funder: Suomen Kulttuurirahasto; doi: http://dx.doi.org/10.13039/501100003125Land plants evolved multiple adaptations to restrict transpiration. However, the underlying molecular mechanisms are not sufficiently understood. We used an ozone-sensitivity forward genetics approach to identify Arabidopsis thaliana mutants impaired in gas exchange regulation. High water loss from detached leaves and impaired decrease of leaf conductance in response to multiple stomata-closing stimuli were identified in a mutant of MURUS1 (MUR1), an enzyme required for GDP-l-fucose biosynthesis. High water loss observed in mur1 was independent from stomatal movements and instead could be linked to metabolic defects. Plants defective in import of GDP-l-Fuc into the Golgi apparatus phenocopied the high water loss of mur1 mutants, linking this phenotype to Golgi-localized fucosylation events. However, impaired fucosylation of xyloglucan, N-linked glycans, and arabinogalactan proteins did not explain the aberrant water loss of mur1 mutants. Partial reversion of mur1 water loss phenotype by borate supplementation and high water loss observed in boron uptake mutants link mur1 gas exchange phenotypes to pleiotropic consequences of l-fucose and boron deficiency, which in turn affect mechanical and morphological properties of stomatal complexes and whole-plant physiology. Our work emphasizes the impact of fucose metabolism and boron uptake on plant-water relations

Author Correction: Genome sequencing and population genomic analyses provide insights into the adaptive landscape of silver birch

International audienc