Regulation of Photosynthesis

The group of Dr. Ute Armbruster aims to identify and characterize regulatory mechanisms of photosynthesis. Particular focus is on the question of how photosynthesis is regulated to achieve efficiency in fluctuating light conditions.

Towards a comprehensive understanding of dynamic photosynthesis

Plant physiology and metabolism are fueled by sunlight. The essential biological process, which harnesses light to produce metabolic energy and oxygen, is coined photosynthesis. Despite the importance of photosynthesis for our life on earth, we still have a very limited understanding of how this process proceeds in nature, where sunlight availability often strongly fluctuates and other environmental stresses occur.

In nature, light availability can vary drastically as can be seen on this picture from the woods.

To fill this gap in knowledge and increase our understanding of plant photosynthesis in dynamic light environments, my research team employs an interdisciplinary approach by linking biochemistry with biophysical methods, spectroscopic plant phenotyping, metabolomics and genetics. Using the model plant Arabidopsis thaliana (Arabidopsis) and Solanum lycopersicum (tomato) as a vegetable crop, our motivated goal is to define the molecular requirements for dynamic photosynthesis. Therefore, we address questions at multiple time scales, from (i) seconds (rapid responses) to (ii) days (acclimation) to (iii) evolution (adaptation). Additionally, we seek to understand (iv) how dynamic photosynthesis interacts with abiotic stresses.

(i)             Which molecular mechanisms underlie rapid responses of photosynthesis?

Changes in light intensity directly affect the photosynthetic electron transport reactions located in the thylakoid membrane of plants. My group aims to identify the key signals of dynamic photosynthesis and proteins that sense these signals and elicit appropriate responses.

Fig.1 The expression of different KEA3 isoforms has distinct effects on photoprotective non-photochemical quenching (NPQ, Armbruster et al., 2016).
(A) NPQ monitored during alternating low light or high light.
(B) Proteins extracted from the transformed tobacco sections were immunodetected with the specific KEA3 antibody.
(C) Images of the transformed tobacco leaf during induction and relaxation of NPQ.
(D, E) Models of KEA3.2-GFP (D) and KEA3.3-GFP (E) in the thylakoid membrane (T).

Presently, we focus on describing the regulation and molecular function of photosynthesis-optimizing thylakoid ion transporters (Armbruster et al., 2014; Armbruster et al., 2016; Höhner et al., 2019; Correa Galvis et al., 2020, Fig. 1).

To identify metabolic signals and their protein targets, we have teamed up with the lab of Aleksandra Skirycz to develop a method to separate thylakoid protein-metabolite complexes and characterize their molecular composition by mass spectrometry.

 

(ii)            How do plants acclimate to dynamic light environments?

As plants evolved to be sessile, they acquired remarkable phenotypic plasticity. Therefore, plants have the ability to drastically alter their physiology and morphology to cope optimally with the prevailing environmental conditions. To date nearly all research on the light acclimation of plants has been performed under “flat day” conditions, where light is switched on in the morning and remains at the same intensity until being switched off at night. However, in their natural habitats, plants experience a ”sinusoidal day” with slowly increasing light intensities peaking at noon, followed by a slow decrease until dawn. Additionally, light intensity in nature often strongly fluctuates. Consequently, a systematic analysis of plant acclimation is highly warranted that bridges experimental with natural light conditions. We have started such analysis at the physiological and biochemical level. Here, we focus on characterizing the acclimation responses of the thylakoid membranes and the embedded light reactions of photosynthesis.

(iii)           How does plant adaptation shape dynamic photosynthesis?

So far, little is known about how plants differ in their capacity for dynamic photosynthesis and how this has been shaped by the environment at the genetic level. Previously, we found different Arabidopsis accessions to have strong phenotypic variations in their acclimation response to dynamic light environments (Kaiser et al., 2020). In the future, we will further explore this finding by EPPN-supported use of the Phenovator at Wageningen University, which allows simultaneous measurements of several growth and photosynthesis related parameters of a large number of Arabidopsis accessions.

Fig 2. Different Arabidopsis accessions vary greatly in their acclimation response to dynamic light environments. The ratio between parameters under dynamic (FL) and stable light conditions (CL) is shown for 36 different randomly chosen Arabidopsis accessions (Kaiser et al., 2020). PLA, projected leaf area; ΦPSII, quantum efficiency of PSII; Fv/Fm, maximum quantum yield of PSII; NPQ, non-photochemical quenching.

Complimentarily, we will perform metabolomics and lipodomics analyses. Subsequently, we will use genome wide association studies to identify genetic determinants of differences in dynamic photosynthesis and associated metabolic signatures. By this approach, we aim at systematically uncovering the genetic, metabolic and physiological framework that underlies dynamic photosynthesis in Arabidopsis. 

(iv)           How does dynamic photosynthesis interact with abiotic stress?

A trinational consortium funded by ERA-CAPS seeks to understand how drought and salt stress affect dynamic photosynthesis and how thylakoid ion transport proteins link respective plant responses. One experimental focus of this consortium, which is led by my lab, is on deciphering the photosynthetic and metabolic acclimation of tomato introgression lines under drought stress and identify causal genes.



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