Plants are sessile organisms, thus for survival they have to cope with every possible change in the environment surrounding them. Every change that deviates from the optimal growth conditions is regarded as a stress for plants. One of the quickest stress responses is stomatal closure which is required during drought to stop loss of water via transpiration and also to prevent entrance of toxic compounds and pathogens into leaves. The broader aim of our research is to study mechanims by which plants sense changes in the environment. As a tool for our research we use Arabidopsis mutants and mutant screens. Furthermore natural variation among Arabidopsis exotypes is used as a source of genetic information and the long standing aim is to transfer knowledge collected from the model species to crops and trees.
The research carried out in the lab can be divided into three interconnected topics
Stomatal signaling (PI Hannes Kollist)
Life on earth largely relies on photosynthesis - a process where atmospheric CO2 is converted to carbohydrates by plants. A key question for plants is how to facilitate sufficient CO2 uptake while preventing excessive loss of water. This is controlled by stomata, microscopic pores in the epidermis of plant leaves surrounded by a pair of guard cells. Stomata also restrict the entry of ozone - a major air pollutant with increasingly negative impact on crop yields, global carbon fixation, and climate change.
We study plant stomatal regulation in response to airborne signals such as ozone, but also CO2, humidity and light. In this research we mainly use the model plant Arabidopsis thaliana and custom made gas-exchange system which enables monitoring stomatal responses in intact plants. Responses of eight plants can be followed in parallel. Our recent developments include smaller (2.5 cm in diameter) custom made gas-exchange cuvette for monitoring stomatal responses of single leaf and bigger (4 litre) cuvette for monitoring whole-plant stomatal responses of larger plants such as tobacco, birch, poplar et cetera. Our ongoing developments are focused on developing systems which would enable manipulations with single guard cells of intact plant leaves and monitoring their electrical and light-emssion based responses to airborne signals.
Our gas-exchange devices were instrumental in identification of the guard cell plasma membrane S-type anion channel, SLAC1, which is essential for stomatal closure in response to ozone, CO2, humidity and light, but also to ABA, NO and Ca2+. Later we showed that SLAC1 is regulated by protein kinase OST1 and that OST1-dependent regulation of SLAC1 is essential for stomatal response to ozone and CO2. Activation of SLAC1 leads to anion efflux and concomitant membrane depolarization leads to activation of voltage-dependent ion channels such as R-type anion channels and K+-efflux channels. In the case of abscisic acid-inuduced stomatal closure the general mechanism leading to the activation of OST1 and SLAC1 is fairly well resolved, however how various airborne signals lead to the activation of SLAC1 is not resolved. The latter is the main target of our research.
Some recent works
Kollist et al 2011 FEBS Journal.
Xue et al. 2011 EMBO Journal.
Vahisalu et al. 2010 Plant Journal.
Vahisalu et al. 2008 Nature
Kollist et al. 2007 Phys. Plant.
NAE signaling (PI Yuh-Shuh Wang)
N-acylethanolamines (NAEs) are a group of fatty acid amides that are composed of a fatty acid and an ethanolamine. NAE 20:4, with 20 carbons and 4 double bonds in its fatty acid moiety, also known as anandamine, has been intensively studied in animal research due to its involvement in the endocanabinoid signaling. Several other NAEs, in addition to NAE 20:4, have also been found to modulate a wide range of physiological and behavioral processes in mammals.
NAEs have also been identified in several plant species, and their levels varied in response to environmental and developmental cues. Exogenously applied NAEs (NAE 12:0 and 18:2) inhibited Arabidopsis seedling growth. In addition, exogenous NAE 12:0 and ABA had a synergistic inhibitory effect on seedling growth. Arabidopsis overexpressing a fatty acid amide hydrolase (AtFAAH), an enzyme that metabolizes NAEs, had a lower NAE content and could overcome the growth inhibitory effects of exogenous NAEs. Surprisingly, the AtFAAH-overexpressing plants were hypersensitive to exogenous ABA, in contradictory to the prediction of being more resistant to ABA due to lower endogenous NAE levels. Furthermore, plants expressing mutated FAAHs of which the amidase activity was abolished still showed hypersensitivity to ABA. An AtFAAH-GFP construct, when expressed in Arabidopsis, conferred NAE tolerance in transgenic plants. However, the AtFAAH-GFP-expressing plants also showed slightly higher resistance to ABA than wild-type plants.
We propose that NAE and ABA signalings interact, at least in part, via FAAH-mediated protein-protein interactions that require accesses to the C-terminus of FAAH. We are currently applying molecular genetics approaches, such as split-ubiquitin membrane yeast two-hybrid and reverse genetic screens, to identify potential components involved in the crosstalk between NAE and ABA signalings.
Some recent works
Li Kang, Yuh-Shuh Wang, Srinivasa Uppalapati, Keri Wang, Yuhong Tang, Vatsala Vadapalli, Barney Venables, Kent Chapman, Elison Blancaflor, and Kirankumar Mysore (2008) Overexpression of a fatty acid amide hydrolase compromises innat immunity in Arabidopsis. The Plant Journal 56: 336-349
Neal D. Teaster, Christy M. Motes, Yuhong Tang, William C. Wiant, Matthew Q. Cotter, Yuh-Shuh Wang, Aruna Kilaru, Barney J. Venables, Karl J. Hasenstein, Cabriel Gonzalez, Elison B. Blancaflor, and Kent D. Chapman (2007) N-Acylethanolamine metabolism interacts with abscisic acid signaling in Arabidopsis thaliana seedlings. Plant Cell 19: 2454-2469
Yuh-Shuh Wang, Rhidaya Shrestha, Aruna Kilaru, William Wiant, Barney J. Venables, Kent D. Chapman, and Elison B. Blancaflor (2006) Manipulation of Arabidopsis fatty acid amide hydrolase expression modifies plant growth and sensitivity to N-acylethanolamines. Proc. Natl. Acad. Sci. USA 103: 12197-12202
Christy M. Motes, Priit Pechter, Cheol Min Yoo, Yuh-Shuh Wang, Kent D. Chapman, and Elison B. Blancaflor (2005) Differential effects of 1-butanol and N-acylethanolamine (NAE) on in vivo cytoskeletal organization and Arabidopsis seedling growth: Implications for NAE mode of action in plant cells. Protoplasma 226: 109-123
Elison B. Blancaflor, Christy M. Motes, Yuh-Shuh Wang, Li Kang, Kirankumar S. Mysore, and Kent D. Chapman (2006) N-Acylethanolamines: Lipid mediators of plant cytoskeletal organization and response to environmental stress. In: Biology of Plant-Microbe Interactions, Vol. 5, (Sánchez, F., Quinto, C., López-Lara, I.M., and Geiger, O. eds), pp. 163-170
Natural variation as molecular tools (PI Mikael Brosche)
The model species Arabidopsis thaliana have a wide distribution range and seeds have been collected that are distributed through stock centers (www.arabidopsis.info; www.arabidopsis.org). This makes Arabidopsis a suitable tool for genome wide association mapping and QTL mapping. A selection of 1001 ecotypes are currently sequenced which will provide a rich source of data to facilitate mapping projects (http://1001genomes.org/). We use several ecotype and recombinant inbred line mapping populations to find genes involved in N-acylethanolamines (NAEs) signaling and in regulation of emission of volatile organic compounds (VOCs).
In addition several single mutants of long time charachterized defense regulators (e.g. coi1, abi1, ein2, eds1, abi1) are studied for their role in regulation of biosynthesis of the important antioxidant ascorbic acid.
Some recent works
Brosché M., Merilo E., Mayer F., Pechter P., Puzõrjova I., Brader G., Kangasjärvi J. and Kollist H. 2010. Natural variation in ozone sensitivity among Arabidopsis thaliana accessions and its relation to stomatal conductance. Plant Cell Environ. 33: 914-925.
Vaahtera L. and Brosché M. 2011. More than the sum of its parts - How to achieve a specific transcriptional response to abiotic stress. Plant Sci. 180: 421-430.
Blomster T., Salojärvi J., Sipari N., Brosché M., Ahlfors R., Keinänen M., Overmyer K. and Kangasjärvi J. 2011. Apoplastic reactive oxygen species transiently decrease auxin signaling and cause stress-induced morphogenic response in Arabidopsis. Plant Physiol. 157: 1866-1883.
Brosché M. and Kangasjärvi J. 2011. Low antioxidant concentrations impact on multiple signalling pathways in Arabidopsis thaliana partly through NPR1. J. Exp. Bot. In press
Vainonen J.P., Jaspers P., Wrzaczek M., Lamminmäki A., Reddy R.A., Vaahtera L., Brosché M. and Kangasjärvi J. 2011. RCD1-DREB2A interaction in leaf senescence and stress responses in Arabidopsis thaliana. Biochem. J. Immediate Publication, doi:10.1042/BJ20111739