Mitogeen-aktiveeritud proteiinkinaaside, MPK4 ja MPK12, roll õhulõhede vastuses CO2 kontsentratsiooni muutustele

Väitekirja elektrooniline versioon ei sisalda publikatsiooneTaimed on elu aluseks Maal. Nad toodavad süsihappegaasist ja veest fotosünteesi käigus orgaanilisi ühendeid ning kõrvalsaadusena vabaneb ka loomseks eluks vajalik hapnik. Õhulõhed on taimelehel asuvad avad, mille kaudu toimub taime gaasivahetus ümbritseva keskkonnaga. Iga õhulõhe on ääristatud kahe sulgrakuga, mis reguleerivad õhulõhede avanemist ja sulgumist. Õhulõhede avanemise põhjustab valgus, madal CO2 kontsentratsioon ja kõrge õhuniiskus, sulgumise aga pimedus, kõrge CO2 kontsentratsioon, madal õhuniiskus, taimehormoonid, patogeenid ja õhu saasteained. Õhulõhede avanemine soodustab taime kasvu, kuna avatud õhulõhede kaudu jõuab taime fotosünteesiks vajalik CO2, samas aga suureneb ka vee aurustumine taimest, mis põuatingimustes võib viia taime närbumiseni. Seetõttu on õhulõhede avatuse täpne regulatsioon ülioluline, optimeerimaks taime kasvu erinevates stressitingimustes. Suurenev CO2 kontsentratsioon atmosfääris vähendab õhulõhede avatust ja vee aurustumist taimest. Kuidas aga toimub sulgrakkudes CO2 mõjul signaaliülekanne, mis viib õhulõhede sulgumiseni, pole praegusel ajal veel täpselt teada. Antud töö tulemused aitavad mõista, kuidas taimed reguleerivad õhulõhede avatust CO2 kontsentratsiooni muutuse toimel. Töö käigus tehti kindlaks, et mitogeen-aktiveeritud proteiinkinaasid, MPK4 ja MPK12, on ühtedeks varaseimateks komponentideks signaaliülekanderajas, mis viib kõrge [CO2] mõjul õhulõhede sulgumiseni. Töö käigus saadud teadmiste põhjal pakuti välja ka mudel MPK4 ja MPK12 rolli kohta õhulõhede vastuses CO2 kontsentratsiooni muutustele. Antud töö tulemused aitavad kaasa selliste toidutaimede aretamisele, mis oleksid piisavalt saagikad ka tulevikukliimas, kõrgema atmosfääri CO2 kontsentratsiooni ja piiratud veevarude tingimustes.Plants are essential to life on Earth – in the process of photosynthesis, they convert carbon dioxide (CO2) and water into organic compounds, and oxygen is released as a by-product. Stomatal pores, that are on the surfaces of the majority of the aerial parts of plants, facilitate gas exchange between plants and the external atmosphere. Each stomatal pore is surrounded by two highly specialized guard cells which sense various endogenous and environmental stimuli, such as CO2, light, temperature, hormones and pathogens and adjust the stomatal pore size to balance CO2 uptake for photosynthesis and loss of water vapour through transpiration. Since water availability is a major constraint of crop yield and is the single most important factor limiting food production, appropriate control of stomatal pore size is essential for the optimization of plant growth. Continuing rise in atmospheric [CO2] increases [CO2] inside the leaves and causes a reduction in stomatal apertures. This, in turn, reduces water loss from plants. Thus, CO2-induced stomatal closure may improve plant water use efficiency and optimization of CO2-controlled stomatal movements may enable breeding of crops that conserve water while maximizing photosynthesis. Presently, the molecular mechanisms by which plants sense CO2 concentration and transduce the CO2 signal to regulate water loss, are not fully understood. This thesis contributes to the understanding of the mechanism how the CO2 signal is transduced in the guard cells and proposes a new model for stomatal CO2-signalling. This study revealed that mitogen-activated protein kinases (MPKs) MPK4 and MPK12 are among the earliest CO2 signalling components presently known in guard cells and that CO2-signal is transmitted through MPK4 and MPK12 leading to activation of guard cell anion channels and closing of stomata. With the continuous increase in atmospheric CO2 levels and the need for breeding crops that would display optimal water use efficiencies, these findings are important for developing strategies for breeding crops suitable for future climates by specific modulation of CO2-dependent stomatal movements.https://www.ester.ee/record=b523466

Eesti elanikkonna hoiakud immigratsiooni suhtes 2004-2010

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Natural Variation in Arabidopsis Cvi-0 Accession Reveals an Important Role of MPK12 in Guard Cell CO2 Signaling

Author Summary Human activities have increased the concentrations of CO2 and harmful air pollutants such as ozone in the troposphere. These changes can have detrimental consequences for agricultural productivity. Guard cells, which form stomatal pores on leaves, regulate plant gas exchange. To maintain photosynthesis, stomata open to allow CO2 uptake, but at the same time, open stomata lead to loss of water and allow the entrance of ozone. Elevated atmospheric CO2 levels reduce stomatal apertures, which can improve plant water balance but also increases leaf temperature. Using genetic approaches—in which we exploit natural variation and mutant analysis of thale cress (Arabidopsis thaliana)—we find that MITOGEN-ACTIVATED PROTEIN KINASE 12 (MPK12) and its inhibitory interaction with another kinase, HIGH LEAF TEMPERATURE 1 (HT1) (involved in guard cell CO2 signaling), play a key role in this regulatory process. We have therefore identified a mechanism in which guard cell CO2 signaling regulates how efficiently plants use water and cope with the air pollutant ozone.Peer reviewe

Up-regulated expression of AOS-LOXa and increased eicosanoid synthesis in response to coral wounding.

In octocorals, a catalase-like allene oxide synthase (AOS) and an 8R-lipoxygenase (LOX) gene are fused together encoding for a single AOS-LOX fusion protein. Although the AOS-LOX pathway is central to the arachidonate metabolism in corals, its biological function in coral homeostasis is unclear. Using an acute incision wound model in the soft coral Capnella imbricata, we here test whether LOX pathway, similar to its role in plants, can contribute to the coral damage response and regeneration. Analysis of metabolites formed from exogenous arachidonate before and after fixed time intervals following wounding indicated a significant increase in AOS-LOX activity in response to mechanical injury. Two AOS-LOX isoforms, AOS-LOXa and AOS-LOXb, were cloned and expressed in bacterial expression system as active fusion proteins. Transcription levels of corresponding genes were measured in normal and stressed coral by qPCR. After wounding, AOS-LOXa was markedly up-regulated in both, the tissue adjacent to the incision and distal parts of a coral colony (with the maximum reached at 1 h and 6 h post wounding, respectively), while AOS-LOXb was stable. According to mRNA expression analysis, combined with detection of eicosanoid product formation for the first time, the AOS-LOX was identified as an early stress response gene which is induced by mechanical injury in coral

Experimental design of wounding stress.

<p>The location and time of sampling shown on a coral colony.</p

Quantitative real-time PCR analysis of transcript levels of <i>C. imbricata AOS-LOXa</i> and <i>AOS-LOXb</i>.

<p>Changes in gene expression in response to wounding within one colony: A) accumulative response; B) secondary response; C) systemic response. D) Response to a single wound. Data are means ± standard error, asterisk indicates significantly higher or lower expression relative to control (<i>P</i><0.05).</p

RP-HPLC analysis of incubation products of C. <i>imbricata</i> tissue homogenate.

<p>A) Radio chromatogram of the products formed from [1⁻¹⁴C] AA by coral homogenate, extracted ion current (EIC) corresponding to α-ketol ([M⁻] = 335.2, peak 2), cyclopentenone ([M⁻] = 317.2, peak 3) and HETE ([M⁻] = 319.2, peak 3). B) The conversion of [1⁻¹⁴C] AA into unidentified polar compounds (UPC) (peak 1) and α-ketol (peak 2) in response to wounding. CPM - counts per minute.</p

List of primers: (a) degenerative primers used for isolation of the target genes, (b) primers used for 5′-3′ RACE and (c) qPCR primers used for gene expression analysis.

<p>Up - forward primer, down - reverse primer; all sequences are presented in the 5′ to 3′ direction.</p

RP-HPLC analysis of incubation products of <i>C. imbricata</i> AOS-LOX fusion proteins expressed in <i>E. coli</i>.

<p>Bacterial extracts expressing the fusion proteins. M, protein molecular weight marker (Fermentas); Neg, negative control, pET11a vector without insert; ALa, AOS-LOXa; ALb, AOS-LOXb. The RP-HPLC analysis of the conversion of [1⁻¹⁴C] AA by AOS-LOXa (peaks 2, 3) and AOS-LOXb (peak 1). The peak numbers indicate identical compounds formed by the coral homogenate (Fig. 2A, and corresponding EIC) and expressed AOS-LOX proteins. EIC [M⁻] = 155.1 corresponding to the main AOS-LOXb product (peak 1). CPM - counts per minute.</p