Õhulõhede juhtivust ja tundlikkust mõjutavad signalisatsioonirajad

Väitekirja elektrooniline versioon ei sisalda publikatsiooneTaimede ellujäämine muutuvas keskkonnas sõltub taimelehtede pinnal asuvatest mikroskoopilise suurusega õhulõhedest. Õhulõhed koosnevad kahest sulgrakust ja nende vahele jäävast õhupilust ning reguleerivad taimede gaasivahetust. Fotosünteesiks vajalik CO2 siseneb lehte läbi õhulõhede, samaaegselt väljub juurtega omastatud vesi transpiratsiooni käigus. Õhulõhede juhtivus on oluline lehe füsioloogiline tunnus, mis väljendab veeauru eraldumise kiirust lehepinnalt ning määrab taimede kasvu, stressitaluvuse ning tootlikkuse. Keskkonnast ja taimesisestest signaalidest lähtuv õhupilu laiuse kiire ja õhulõhede tiheduse pikemas ajaskaalas toimuv regulatsioon määravad õhulõhede juhtivuse väärtuse. Käesolevas töös uurisime taimehormooni abstsiishappe (ABA) rolli õhulõhede juhtivuse reguleerimisel ning leidsime, et mida väiksem oli ABA sisaldus lehes, seda kõrgem oli õhulõhede juhtivus. Kõrgem õhulõhede juhtivus tulenes laiemast õhupilust ning suuremast õhulõhede tihedusest. Seega kaotasid ABA-defitsiitsed taimed transpiratsiooni käigus rohkem vett, samas olid nad sellegipoolest võimelised sulgema õhupilusid stressitingimustes. Lisaks leidsime, et õhulõhede sulgrakud ning floeemi saaterakud on olulised ABA biosünteesi kohad. OST1, üks olulisemaid valke ABA signaalrajas, reguleeris õhulõhede tundlikkust vastusena keskkonnatingimustele ja ABA-le, kuid ei osalenud õhulõhede tiheduse määramisel. Lisaks uurisime farnesüleerimist läbiviiva valgu ERA1 rolli õhulõhede regulatsioonis ning leidsime, et ERA1 osaleb õhulõhede juhtivuse määramises ning sinise valguse põhjustatud õhupilude avanemises. Õhulõhede arengu ning avanemise ja sulgumise regulatsiooni mõistmine on oluline, et aretada erinevatesse keskkonnatingimustesse sobivaid taimi, mis oleks ühtpidi efektiivsema vee kasutusega, kuid samas võimalikult kõrge fotosünteesiga ning sellest tulenevalt saagikamad.Survival of plants in the changing environment depends largely on stomata, small pores surrounded by a pair of specialized guard cells on the aerial surface of plants. Stomata control gas exchange between the leaf and atmosphere – uptake of CO2 for photosynthesis and loss of water through transpiration. Plant growth, stress-related water management and production depend on the appropriate control of stomatal conductance, one of the most important leaf physiological traits. Rapid changes in the stomatal aperture width and changes in the number of stomata (stomatal density) on a longer timescale both affect stomatal conductance and enable to regulate it according to endogenous and environmental cues. We studied the role of plant hormone abscisic acid (ABA) in controlling stomatal conductance and found that reduced leaf ABA concentration led to higher stomatal conductance. This was associated with wider stomatal aperture width and increased stomatal density of these plants. ABA-deficient plants thus lost more water to the atmosphere, but were still able to respond to environmental changes with stomatal closure. We found that stomatal guard cells and phloem companion cells were important sources of ABA. We showed that OST1, a key positive regulator of ABA signalling, was important in stomatal responsiveness to environmental factors and ABA, but it was not involved in regulating stomatal development. Stomatal regulation by a farnesylating protein ERA1, which is suggested to be involved in ABA signalling, was also studied. We revealed that ERA1 is involved in determining the stomatal conductance and mediating the blue light-induced opening response. Understanding the mechanism of stomatal regulation gives information for breeding crop plants productive in different climatic conditions. The focus is on developing more water use efficient plants with reduced stomatal conductance without compromising in photosynthesis and ultimately, in crop yields.https://www.ester.ee/record=b524410

The Role of ENHANCED RESPONSES TO ABA1 (ERA1) in Arabidopsis Stomatal Responses Is Beyond ABA Signaling

Proper stomatal responses are essential for plant function in an altered environment. The core signaling pathway for abscisic acid (ABA)-induced stomatal closure involves perception of the hormone that leads to the activation of guard cell anion channels by the protein kinase OPEN STOMATA1. Several other regulators are suggested to modulate the ABA signaling pathway, including the protein ENHANCED RESPONSE TO ABA1 (ERA1), that encodes the farnesyl transferase beta-subunit. The era1 mutant is hypersensitive to ABA during seed germination and shows a more closed stomata phenotype. Using a genetics approach with the double mutants era1 abi1-1 and era1 ost1, we show that while era1 suppressed the high stomatal conductance of abi1-1 and ost1, the ERA1 function was not required for stomatal closure in response to ABA and environmental factors. Further experiments indicated a role for ERA1 in blue light-induced stomatal opening. In addition, we show that ERA1 function in disease resistance was independent of its role in stomatal regulation. Our results indicate a function for ERA1 in stomatal opening and pathogen immunity.Peer reviewe

Arabidopsis mutant dnd2 exhibits increased auxin and abscisic acid content and reduced stomatal conductance

Arabidopsis thaliana cyclic nucleotide-gated ion channel gene 4 (AtCNGC4) loss-of-function mutant dnd2 exhibits elevated accumulation of salicylic acid (SA), dwarfed morphology, reduced hypersensitive response (HR), altered disease resistance and spontaneous lesions on plant leaves. An orthologous barley mutant, nec1, has been reported to over-accumulate indole-3-acetic acid (IAA) and to exhibit changes in stomatal regulation in response to exogenous auxin. Here we show that the Arabidopsis dnd2 over-accumulates both IAA and abscisic acid (ABA) and displays related phenotypic and physiological changes, such as, reduced stomatal size, higher stomatal density and stomatal index. dnd2 showed increased salt tolerance in root growth assay and significantly reduced stomatal conductance, while maintaining near wt reaction in stomatal conductance upon external application of ABA, and probably consequently increased drought stress tolerance. Introduction of both sid2-1 and fmo1 into dnd2 background resulting in removal of SA did not alter stomatal conductance. Hence, the closed stomata of dnd2 is probably a result of increased ABA levels and not increased SA levels. The triple dnd2sid2abi1-1 mutant exhibited intermediate stomatal conductance compared to dnd2 and abil-1 (ABA insensitive, open stomata), while the response to external ABA was as in abi1-1 suggesting that reduced stomatal conductance in dnd2 is not due to impaired ABA signaling. In conclusion, Arabidopsis dnd2 mutant exhibited ABA overaccumulation and stomatal phenotypes, which may contribute to the observed improvement in drought stress resistance. Thus, Arabidopsis dnd2 mutant may serve as a model for studying crosstalk between biotic and abiotic stress and hormonal response in plants.Peer reviewe