102 research outputs found
Interaction of methyl viologen-induced chloroplast and mitochondrial signalling in Arabidopsis
Reactive oxygen species (ROS) are key signalling intermediates in plant
metabolism, defence, and stress adaptation. In plants, both the
chloroplast and mitochondria are centres of metabolic control and ROS
production, which coordinate stress responses in other cell
compartments. The herbicide and experimental tool, methyl viologen (MV)
induces ROS generation in the chloroplast under illumination, but is
also toxic in non-photosynthetic organisms. We used MV to probe plant
ROS signalling in compartments other than the chloroplast. Taking a
genetic approach in the model plant Arabidopsis (Arabidopsis thaliana),
we used natural variation, QTL mapping, and mutant studies with MV in
the light, but also under dark conditions, when the chloroplast electron
transport is inactive. These studies revealed a light-independent
MV-induced ROS-signalling pathway, suggesting mitochondrial involvement.
Mitochondrial Mn SUPEROXIDE DISMUTASE was required for ROS-tolerance
and the effect of MV was enhanced by exogenous sugar, providing further
evidence for the role of mitochondria. Mutant and hormone feeding assays
revealed roles for stress hormones in organellar ROS-responses. The
radical-induced cell death1 mutant, which is tolerant to MV-induced ROS
and exhibits altered mitochondrial signalling, was used to probe
interactions between organelles. Our studies suggest that mitochondria
are involved in the response to ROS induced by MV in plants.</p
Evolutionary conservation and post-translational control of S-adenosyl-L-homocysteine hydrolase in land plants
Trans-methylation reactions are intrinsic to cellular metabolism in all living organisms. In land plants, a range of substrate-specific methyltransferases catalyze the methylation of DNA, RNA, proteins, cell wall components and numerous species-specific metabolites, thereby providing means for growth and acclimation in various terrestrial habitats. Trans-methylation reactions consume vast amounts of S-adenosyl-L-methionine (SAM) as a methyl donor in several cellular compartments. The inhibitory reaction by-product, S-adenosyl-L-homocysteine (SAH), is continuously removed by SAH hydrolase (SAHH), which essentially maintains trans-methylation reactions in all living cells. Here we report on the evolutionary conservation and post-translational control of SAHH in land plants. We provide evidence suggesting that SAHH forms oligomeric protein complexes in phylogenetically divergent land plants and that the predominant protein complex is composed by a tetramer of the enzyme. Analysis of light-stress-induced adjustments of SAHH inArabidopsis thalianaandPhyscomitrella patensfurther suggests that regulatory actions may take place on the levels of protein complex formation and phosphorylation of this metabolically central enzyme. Collectively, these data suggest that plant adaptation to terrestrial environments involved evolution of regulatory mechanisms that adjust the trans-methylation machinery in response to environmental cues
Arabidopsis RCD1 coordinates chloroplast and mitochondrial functions through interaction with ANAC transcription factors
Reactive oxygen species (ROS)-dependent signaling pathways from chloroplasts and mitochondria merge at the nuclear protein RADICAL-INDUCED CELL DEATH1 (RCD1). RCD1 interacts in vivo and suppresses the activity of the transcription factors ANAC013 and ANAC017, which mediate a ROS-related retrograde signal originating from mitochondrial complex III. Inactivation of RCD1 leads to increased expression of mitochondrial dysfunction stimulon (MDS) genes regulated by ANAC013 and ANAC017. Accumulating MDS gene products, including alternative oxidases (AOXs), affect redox status of the chloroplasts, leading to changes in chloroplast ROS processing and increased protection of photosynthetic apparatus. ROS alter the abundance, thiol redox state and oligomerization of the RCD1 protein in vivo, providing feedback control on its function. RCD1-dependent regulation is linked to chloroplast signaling by 3'-phosphoadenosine 5'-phosphate (PAP). Thus, RCD1 integrates organellar signaling from chloroplasts and mitochondria to establish transcriptional control over the metabolic processes in both organelles.Peer reviewe
Detecting early signs of heat and drought stress in Phoenix dactylifera (date palm)
Plants adapt to the environment by either long-term genome evolution or by acclimatization processes where the cellular processes and metabolism of the plant are adjusted within the existing potential in the genome. Here we studied the adaptation strategies in date palm, Phoenix dactylifera, under mild heat, drought and combined heat and drought by transcriptomic and metabolomic profiling. In transcriptomics data, combined heat and drought resembled heat response, whereas in metabolomics data it was more similar to drought. In both conditions, soluble carbohydrates, such as fucose, and glucose derivatives, were increased, suggesting a switch to carbohydrate metabolism and cell wall biogenesis. This result is consistent with the evidence from transcriptomics and cis-motif analysis. In addition, transcriptomics data showed transcriptional activation of genes related to reactive oxygen species in all three conditions (drought, heat, and combined heat and drought), suggesting increased activity of enzymatic antioxidant systems in cytosol, chloroplast and peroxisome. Finally, the genes that were differentially expressed in heat and combined heat and drought stresses were significantly enriched for circadian and diurnal rhythm motifs, suggesting new stress avoidance strategies.Peer reviewe
Natural Variation in Arabidopsis Cvi-0 Accession Reveals an Important Role of MPK12 in Guard Cell CO2 Signaling
Plant gas exchange is regulated by guard cells that form stomatal pores.
Stomatal adjustments are crucial for plant survival; they regulate
uptake of CO2 for photosynthesis, loss of water, and entrance of air
pollutants such as ozone. We mapped ozone hypersensitivity, more open
stomata, and stomatal CO2-insensitivity phenotypes of the Arabidopsis
thaliana accession Cvi-0 to a single amino acid substitution in
MITOGEN-ACTIVATED PROTEIN (MAP) KINASE 12 (MPK12). In parallel, we
showed that stomatal CO2-insensitivity phenotypes of a mutant cis
(CO2-insensitive) were caused by a deletion of MPK12. Lack of MPK12
impaired bicarbonate-induced activation of S-type anion channels. We
demonstrated that MPK12 interacted with the protein kinase HIGH LEAF
TEMPERATURE 1 (HT1)-a central node in guard cell CO2 signaling-and that
MPK12 functions as an inhibitor of HT1. These data provide a new
function for plant MPKs as protein kinase inhibitors and suggest a
mechanism through which guard cell CO2 signaling controls plant water
management.</p
Multiple strategies to prevent oxidative stress in Arabidopsis plants lacking the malate valve enzyme NADP-malate dehydrogenase
The nuclear-encoded chloroplast NADP-dependent malate dehydrogenase (NADP-MDH) is a key enzyme controlling the malate valve, to allow the indirect export of reducing equivalents. Arabidopsis thaliana (L.) Heynh. T-DNA insertion mutants of NADP-MDH were used to assess the role of the light-activated NADP-MDH in a typical C3 plant. Surprisingly, even when exposed to high-light conditions in short days, nadp-mdh knockout mutants were phenotypically indistinguishable from the wild type. The photosynthetic performance and typical antioxidative systems, such as the Beck–Halliwell–Asada pathway, were barely affected in the mutants in response to high-light treatment. The reactive oxygen species levels remained low, indicating the apparent absence of oxidative stress, in the mutants. Further analysis revealed a novel combination of compensatory mechanisms in order to maintain redox homeostasis in the nadp-mdh plants under high-light conditions, particularly an increase in the NTRC/2-Cys peroxiredoxin (Prx) system in chloroplasts. There were indications of adjustments in extra-chloroplastic components of photorespiration and proline levels, which all could dissipate excess reducing equivalents, sustain photosynthesis, and prevent photoinhibition in nadp-mdh knockout plants. Such metabolic flexibility suggests that the malate valve acts in concert with other NADPH-consuming reactions to maintain a balanced redox state during photosynthesis under high-light stress in wild-type plants
Abscisic Acid Insensitive 4 transcription factor is an important player in the response of Arabidopsis thaliana to two-spotted spider mite (Tetranychus urticae) feeding.
Plants growing in constantly changeable environmental conditions are compelled to evolve regulatory mechanisms to cope with biotic and abiotic stresses. Effective defence to invaders is largely connected with phytohormone regulation, resulting in the production of numerous defensive proteins and specialized metabolites. In our work, we elucidated the role of the Abscisic Acid Insensitive 4 (ABI4) transcription factor in the plant response to the two-spotted spider mite (TSSM). This polyphagous mite is one of the most destructive herbivores, which sucks mesophyll cells of numerous crop and wild plants. Compared to the wild-type (Col-0) Arabidopsis thaliana plants, the abi4 mutant demonstrated increased susceptibility to TSSM, reflected as enhanced female fecundity and greater frequency of mite leaf damage after trypan blue staining. Because ABI4 is regarded as an important player in the plastid-to-nucleus retrograde signalling process, we investigated the plastid envelope membrane dynamics using stroma-associated fluorescent marker. Our results indicated a clear increase in the number of stroma-filled tubular structures deriving from the plastid membrane (stromules) in the close proximity of the site of mite leaf damage, highlighting the importance of chloroplast-derived signals in the response to TSSM feeding activity
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