Jaakko Kangasjärvi’s special Issue

This special issue is in tribute to Jaakko Kangasjärvi who has been professor in the Organismal and Evolutionary Biology Research Programme and the dean of the Faculty of Biological and Environmental Sciences at Helsinki University and an active member of the Scandinavian plant physiology society. His research interests and influence encompassed different topics, and we decided to honour all of them by dividing the special issue into 4 themes, each led by prominent scientists in the area.
Original research, technical advances, and short communications are welcome. Reviews are on invitation only.

It is widely believed that one of the key innovations that contributed to the success of the terrestrial flora was the evolution of stomata.  These structures play major roles in the regulation of CO₂ uptake, water loss, pathogen entry and responses to pollutant gases. As such, they impact on photosynthesis and dry matter accumulation, the ability to withstand drought, nutrient uptake, defence, responses to pollutants and provide leaves with some limited cooling capacity. To achieve this, they respond by changing the aperture of the stomatal pore, and/or the number of stomata that develop on the leaf surface, to external environmental signals, such as light, temperature, vapour pressure deficit and the concentration of gases such as CO₂ and ozone. They are also sensitive to changes in internal cues such as the majority of plant hormones.

As a result of decades of work on stomata, we have learned a great deal about the underlying signalling pathways that control stomatal aperture and stomatal development. Most recently, insights from these fundamental studies have been exploited in the translational sense in efforts to improve crop yields and performance in the face of changing environmental conditions brought about by climate change. Even though progress in both the applied and fundamental areas is impressive, there is still much to be done before we have a full understanding of stomata and how they work.

Over many years, Jaakko and his research group made outstanding and lasting contributions to our understanding of how stomata work. These studies were stimulated by his interest in the effects of ozone on plants. This, in turn, prompted him to focus on stomata and his work resulted in key insights into the role of ROS in guard cell signalling and the discovery of the SLAC1 anion channel that is so important in stomatal biology.

We welcome manuscripts describing work in guard cell signalling, including responses to pathogens, pollutant gasses, and plant hormones. Molecular investigations revealing new signalling components are especially welcome, as are more applied investigations. As Jaakko’s interests extended from Arabidopsis to trees, there is no restriction on the plant species that form the basis of the research. We are interested in receiving all article types.

Examples of areas of interest would include:

• Regulation of ion channel activity in guard cells
• ABA signalling
• Responses to pathogens and ozone
• Guard cell ROS signalling
• Stomatal biotechnology in crops and trees

Reactive oxygen species (ROS) are no longer viewed merely as damaging by-products of aerobic metabolism, but as central signalling molecules that control plant stress acclimation, metabolism and development. In pioneering work by Jaakko Kangasjärvi’s group, ozone fumigation was established as a tool to generate a controlled apoplastic oxidative burst. Under these conditions, sensitive genotypes developed a characteristic biphasic ROS burst resembling the hypersensitive response, and hormonal signalling largely determined whether the response was resolved or progressed to cell death. Subsequent studies demonstrated that ROS generated in chloroplasts and mitochondria through photosynthetic and respiratory electron transfer chains, respectively, or in the apoplast by RBOH NADPH oxidases, act as distinct, non-redundant signals with specific biological functions. Many challenging questions remain. How chemically similar, short-lived molecules encode distinct information; how cell compartment-specific signals converge and are decoded in the nucleus; and how these networks operate under naturally fluctuating environmental conditions. We welcome original research articles on all aspects of plant ROS and redox biology. 

The increasing challenges posed by drought, heat waves, soil salinization, and pathogen outbreaks under rapidly changing climate conditions call for a deeper understanding of molecular mechanisms that enable plants to perceive, integrate, and respond to complex environmental cues. Since the first report on the Arabidopsis radical-induced cell death 1 (rcd1) mutant in the year 2000, followed by molecular cloning of the RCD1 gene in 2004, RCD1 and the SIMILAR TO RCD ONE (SRO) protein family have emerged as key signalling hubs in numerous plant stress responses.

SRO proteins occupy central nodes in several stress-regulatory networks, linking redox homeostasis, hormone signalling, and transcriptional regulation. Their integrative role makes SRO proteins promising targets for developing climate-resilient plants. This potential has been recently underscored by the discovery of natural SRO polymorphisms in wheat, maize, and rice that improve abiotic stress tolerance.

Despite their pivotal role in stress signalling networks, the molecular mechanisms underlying SRO protein function remain only partially understood. SRO proteins interact with transcription factors from multiple families via short linear motifs and are thought to function as transcriptional co-regulators. However, the mechanisms by which SRO proteins assemble dynamic transcriptional complexes and integrate multiple signalling pathways remain largely unexplored.

Together with his research team, Jaakko Kangasjärvi identified RCD1, the founding member of the SRO protein family, and made numerous pioneering discoveries that have shaped our current understanding of the biological and molecular functions of RCD1 and other SRO proteins.

We invite submissions that advance our understanding of SRO proteins and their roles in plant biology.

We particularly welcome manuscripts addressing, but not limited to, the following topics:

• Molecular mechanisms and structure–function relationships of SRO proteins, including the functions of the WWE and PARP-like domains
• Mechanisms underlying SRO interactions with transcription factors
• Assembly, regulation, and dynamics of SRO-containing transcriptional complexes, including biomolecular condensates
• Redox regulation of SRO proteins and their roles in reactive oxygen species signalling
• SRO proteins in retrograde signalling
• Molecular mechanisms by which SRO proteins integrate multiple stress signalling pathways
• Functional divergence among SRO paralogues
• SRO natural variation, genome editing, and crop improvement strategies targeting SRO proteins
• Translational studies in crops and field validation of SRO-mediated stress tolerance

Trees dominate terrestrial carbon uptake and experience multiple, overlapping environmental stresses over decades. Despite their ecological and economic importance, our molecular understanding of tree responses to environmental change remains far less developed than that of annual model species. Jaakko Kangasjärvi’s work helped establish molecular genetics, genomics, and systems biology as powerful approaches to dissect environmental responses in long-lived woody species. Studies in silver birch and hybrid aspen showed that reactive oxygen species (ROS) and associated signaling networks are central regulators of tree responses to environmental stress, while also revealing that systemic signaling, whole-plant acclimation, and long-distance communication differ substantially from those in Arabidopsis. Major challenges of current tree research include identifying how trees perceive transient fluctuations in environmental signals and convert them into long-term acclimation, understanding carbon sequestration and wood formation, using genomic and genetic resources to uncover the molecular mechanisms underlying tree growth and stress resilience, and translating genomics and genetics into tree improvement. We invite original research articles on  physiology, molecular genetics, genomics, and environmental  signaling in trees, and comparative studies linking tree species with model plants.