Working at the very heart of photosynthesis

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When flying to attend conferences in the USA, Professor Hans-Henning Kunz can often see the damage even from his plane window: lush green circles in the middle of otherwise pallid fields.

“You see it in wheat fields, for example – monoculture, in many cases, with artificial and circular irrigation.” Other passengers are likely unaware of what lies behind the almost geometric patterns: “Climate change is bringing more and more hot spells. And for many farmers, artificial irrigation is the only way to respond at short notice,” the plant physiologist explains. “However, higher temperatures also mean that more water evaporates, leaving greater concentrations of ions – salts, essentially – in the soil.” In this now heavily ionic environment, it becomes increasingly difficult for plants to draw water from the ground. “The result? Harvest yields dwindle, the soil becomes unproductive and photosynthesis declines.”

The latter point has been the focus of Kunz’s research work since taking up the Chair of Plant Biochemistry and Physiology at LMU’s Biocenter on July 1 last year. “Photosynthesis happens to be the most important reaction in the world. Without it, life would not be possible for us or the animal kingdom,” he says.

Its biochemical reactions are well known: “Light is captured, water molecules are split, electrons and oxygen are released and CO2 is captured. What we do not yet fully understand, though, is the molecular structure of that part of the plant cell – the chloroplast – in which photosynthesis takes place. At LMU’s molecular biology and biochemistry laboratory in Planegg-Martinsried, Kunz and his team are exploring how the many and varied organisms and complex biochemical reactions in chloroplasts operate in parallel. “We are working at the very heart of photosynthesis,” the professor notes. “We want to find out what its minimal components are, which genes are involved and what detracts from photosynthetic efficiency.”

From Germany to the US and back to Munich

A native of Regensburg, Hans-Henning Kunz first studied for a degree in biology at the Technical University (TU) of Kaiserslautern before earning a doctorate in plant biochemistry at the University of Cologne. His work here demonstrated that the nocturnal breakdown of fatty acids is vital to the survival of fully grown Arabidopsis thaliana plants.

Kunz then continued his postdoctoral studies at the University of California in San Diego. His four-year stay here was supported initially by a Feodor Lynen scholarship from the Alexander von Humboldt Foundation and, later, by a research grant under the aegis of the Human Frontier Science Program. In 2014, Kunz was given an assistant professorship at Washington State University. “So, my wife and I moved from the southernmost tip of the American west coast to the northernmost end of the country, from the Mexican border to a place near the Canadian border.” His move to LMU Munich came in summer 2020.

“The position advertised in Munich was hugely tempting,” Professor Kunz admits. “Historically, the Department of Plant Sciences has always had a strong research focus on chloro-plasts.” There is, he says, “a lot of exciting evolution and genetics to discover,” some of which is anchored in TRR175, a focal research project backed by Deutsche For-schungsgemeinschaft, DFG (the German Research Association). This project is devoted to “The Green Hub: The Chloroplast as the Central Coordinator of Acclimation in Plants”. Moreover, Kunz’s predecessor, Professor Jürgen Soll, had also worked in a similar field: “He explored how proteins are transported in chloroplasts; I look at ion transport. The ‘transporters’ that effectively bring ions in and out first enter the chloroplast using a mech-anism discovered by Professor Soll.”

Plants need a lot of ions (charged particles) in the form of potassium, for example – one reason being to adjust what is referred to as the ‘osmotic potential’ of the cells and the chloroplast and to balance the charges. “However, it becomes increasingly difficult for plants to absorb potassium if the soil also contains sodium salts.” These salts are left be-hind when large quantities of water evaporate, as is the case in the USA. “Less photosyn-thesis takes place as a result. But less water is absorbed too, which damages the plants and leads to deteriorating yields.”

Kunz adopts an approach rooted in systems biology: “I’m trying to understand the chloroplast and its phenomena as a system, and to develop a systematic explanation.” He has introduced element analytical methods to the Department of Plant Sciences. Using a procedure he developed at Washington State University, his team at LMU has also already set up what are called ‘micro-RNA libraries’. “We can use these to very quickly knock out genes and chloroplast proteins – and then watch what happens in the organelle.”

The laboratory work centers around model organisms taken from Arabidopsis thaliana or thale cress, a “small, herbaceous, not very spectacular plant.” Long since sequenced, its genome is of a manageable size, which Kunz sees as ideal for a model organism. In biology, plant cultivation pursues two contrary aspirations: “On the one hand, you want to examine the way the plant works per se, so the conditions have to be as constant and reproducible as possible.”

Back when Kunz began his doctoral studies in 2006, researchers therefore still tried to create ideal conditions for their work. The professor nevertheless stresses that, today, researchers also want to understand the impact on plants of environmental factors such as fluctuations in temperature and lighting – factors that exist in the real world. “We want to know how the plant adapts and what genetic processes it uses to do so?” Pronounced lighting variations are thus simulated in the laboratory, as if clouds were intermittently obscuring the sun. Again and again, the professor and his team ask themselves how they can make the findings of their basic research available for bioengineering and plant cultivation purposes. “In recent years, we have gained all kinds of new insights in this area,” Hans-Henning Kunz notes. “Combining these with the latest breakthroughs in gene editing (CRISPR/Cas) and microscopy puts us right on the cusp of a very exciting time for our research.”