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hannes.kollist@ut.ee

Tel: (+372) 73-74-814

Nooruse 1, Tartu 50411

Estonia

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Research

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.

 


1. Guard cell signaling


Coming soon ...

 

 

2. Stomatal regulation of crops


In 2013, we launched a new gas exchange device designed to measure the transpiration and photosynthesis of plants larger than Arabidopsis. This enabled us to initiate studies with crops to clarify whether their stomatal signaling is similar to that of model plant Arabidopsis. We found that wheat and barley closed their stomata in response to darkness, elevated CO2 and high VPD and opened in response to CO2 deprival and blue light just like Arabidopsis did. However, stomatal response half-times were considerably shorter in crops, indicating that their stomatal sensitivity to abiotic environment is higher. Interestingly, we also found that the cross-talk between stomatal closure and opening pathways is species-specific: in case of opposing abiotic signals, the stomata of cereals tended to close, whereas those of Arabidopsis opened. 

 

Publication  in New Phytologist

To open or to close: species-specific stomatal responses to simultaneously applied opposing environmental factors


As crop studies done in the lab provide only half of the picture, we started with field measurements together with Estonian Crop Research Institute in 2015. Measurements of stomatal conductance and photosynthesis with portable devices in the field showed that gas exchange was positively correlated with final grain yield only in the unfavourable year of 2016. When all three study years (2015-2017) were pooled, water use efficiency (photosynthesis divided by transpiration) correlated significantly with grain yield and, according to path analysis, explained 12% of grain yield. 

 

Publication in ScienceDirect

Gas exchange-yield relationships of malting barley genotypes treated with fungicides and biostimulants


Crop studies will definitely continue in our lab: we carry on to study the aspects of crop stomatal signaling as compared to Arabidopsis in different conditions. Moreover, as transpiration ensures leaf cooling and temperatures continue to increase, our next challenge is temperature-induced stomatal regulation of Arabidopsis and crops. 

 

Four-chamber “large plant” device was used to study other non-model plants as well. We added our piece to the ongoing debate on ABA-responsiveness of ferns and found that stomatal closure of ferns in response to ABA is species- and growth-condition dependent. However, even those ferns that responded to ABA did so in a way, which is very different from the fast and extensive ABA-induced closure of Arabidopsis. 

 

Publication in Plant Physiology

Fern Stomatal Responses to ABA and CO2 Depend on Species and Growth Conditions

 

We also found that ABA-deficient mutants of tomato and pea had significantly higher stomatal conductance compared to wildtype plants, but their response to high VPD was intact. This result indicates that VPD-induced stomatal signaling may be partly ABA-independent and may involve passive component as well. 

 

Publication in Plant Physiology

Stomatal VPD Response: There Is More to the Story Than ABA

 

 


3. Biochemistry of organelles

 

ATP production is important for the survival of cells. In eukaryotic organisms, mitochondria produce ATP via oxidative phosphorylation (OXPHOS), and chloroplasts produce it in the course of photosynthesis. We are approaching the biochemistry of organelles from different angles. On the one hand, we are studying mechanisms of mitochondrial DNA (mtDNA) maintenance.

 

Genes that are essential for OXPHOS are encoded by the mtDNA which means that respective maintenance defects are prone to severely influence ATP production. Making use of the ease of the system, we are employing human HEK293 cells in order to study changes to mtDNA-protein complexes (nucleoids) in connection with mitochondria-associated ER-membranes (MAM).

 

On the other hand, we are using plant models in order to understand the influences of photosynthetically and/or OXPHOS derived energy carriers and metabolites. For this, we are monitoring changes to stomate regulation (stomates = structures in plant leaves that enable gas-exchange and transpiration). Stomate regulation requires, among others, activity of H+-ATPases which are depended on proper organelle function.

 

 

Publications

 

Ciprofloxacin impairs mitochondrial DNA replication initiation through inhibition of Topoisomerase 2

 

The epigenetic landscape related to reactive oxygen species formation in the cardiovascular system

 

Human Mitochondrial DNA-Protein Complexes Attach to a Cholesterol-Rich Membrane Structure

 

Replication factors transiently associate with mtDNA at the mitochondrial inner membrane to facilitate replication

 

To be or not to be a nucleoid protein: a comparison of mass-spectrometry based approaches in the identification of potential mtDNA-nucleoid associated proteins.

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