Index

“Cassava Source-Sink“ – Group Wolfgang Zierer

Fig. 1: Storage roots of a 10-month-old cassava plant
Fig. 1: Storage roots of a 10-month-old cassava plant

We strive to improve cassava storage root yield. Cassava is a tropical crop that is consumed by over 800 million people worldwide and is of special importance for the food security of smallholder farmers in Sub-Saharan Africa.

The plant grows up to 3-4 meters in height and generates several starchy storage roots under good conditions. These storage roots (Fig. 1) and their starch are the basis for a multitude of foods.

Fig. 2: A 4-meter tall cassava plant of genotype 60444.
Fig. 2: A 4-meter tall cassava plant of genotype 60444.

Alongside many other options, the storage roots can be consumed as vegetables in cooked or fried state or their starch can be processed into a variety of products, like the African Gari, a popular kind of puree.

Fig. 3: Identification of yield-related genes in leaves, phloem, and storage roots with subsequent combination.
Fig. 3: Identification of yield-related genes in leaves, phloem, and storage roots with subsequent combination.

IUnfortunately, cassava yield is still comparably low in contrast to the heavily yield-optimized crops like wheat or maize. A sustainable cassava yield improvement would therefore have a large impact on the food security of millions of people. Therefore, we dedicate our work towards cassava yield improvement.

This goal is unfortunately not within easy reach and a biotechnological improvement of cassava yield is dependent on a very detailed understanding of the plant. Therefore, our work also contains a lot of basic science to unravel the physiological and biochemical processes of this exiting plant species.

Fig. 4: Different stages of cassava transformation.
Fig. 4: Different stages of cassava transformation.

We mainly research the regulation of carbohydrate metabolism in auto- and heterotrophic tissues, assimilate transport, as well as developmental processes. Within these processes, we are trying to identify genes with positive impact on storage root yield and to combine them eventually for even larger impact (Fig. 3).

Fig. 5: Cassava plants in the greenhouse.
Fig. 5: Cassava plants in the greenhouse.

We test our target genes via transgenic cassava plants, which we generate ourselves or with the help of our collaboration partner at the ETH Zurich. Cassava transformation comprises refined tissue culture protocols, which can regenerate entire plants from dedifferentiated plant cells (Fig. 4).

As a first step, we test our modified cassava plants with various techniques in the greenhouse. Plants that can outperform their unmodified genetic background are of course of special interest for us (Fig. 5).

Fig. 6: Gas-exchange measurements with two measuring devices on a cassava plant.
Fig. 6: Gas-exchange measurements with two measuring devices on a cassava plant.

In addition to the determination of agronomic parameters and different physiological experiments like gas-exchange measurements (Fig. 6), we routinely employ most modern techniques of molecular plant research, like transcriptome- and proteome studies (Fig. 7).

Fig. 7: Example of a weighted gene correlation network analysis with seven different cassava tissues.
Fig. 7: Example of a weighted gene correlation network analysis with seven different cassava tissues.

Several metabolite measurements are part of our routine application as well. Enzymatic or chromatographic sugar measurements for instance, grant us insight into primary plant metabolism (Fig. 8).

Fig. 8: Enzymatic determination of glucose, fructose, and sucrose (A) and chromatographic determination of phosphorylated intermediates (B).
Fig. 8: Enzymatic determination of glucose, fructose, and sucrose (A) and chromatographic determination of phosphorylated intermediates (B).

 

 

Fig. 9: Characterization of a cassava promoter in a stably transformed promoter-reporter plant.
Fig. 9: Characterization of a cassava promoter in a stably transformed promoter-reporter plant.

In addition to the identification and analysis of various genes, we also work on the improvement of tools for the generation of better transgenic cassava plant. Examples are better transformation protocols or the identification of tissue specific promoter sequences (Fig. 9)

Fig. 10: Cassava storage root cross-section containing fluorescent substances.
Fig. 10: Cassava storage root cross-section containing fluorescent substances.

Furthermore, we conduct different studies on cassava wild type plants and various breeding material to understand underlying physiological processes, like the storage root formation or the assimilate transport.

 

Recently, we could clarify the symplasmic connections in cassava stems and storage roots by introducing and following fluorescent substances into the plant (Fig. 10).

Fig. 11: Cassava Source-Sink project partners.
Fig. 11: Cassava Source-Sink project partners.

Our research group is part of the Cassava Source-Sink (www.cass-research.org) project (CASS) and has excess to a large network of plant science techniques and expertise through our various partners (Fig. 11).

 

We have close collaborations with:

  • International Institute of Tropical Agriculture (IITA), Bioscience, Ibadan, Nigeria
  • National Root Crops Research Institute (NRCRI), Umudike, Nigeria
  • Chung-Hsing University (NCHU), Advanced Biotechnology Center, Taichung, Taiwan
  • Sainsbury Laboratory Cambridge University (SLCU), Cambridge, United Kingdom
  • Boyce Thompson Institute, Plant Research (BTI), Ithaca NY, USA
  • Eidgenössische Technische Hochschule (ETH), Chair of Biochemistry, Zurich, Switzerland.
  • Technische Universität Kaiserslautern, Chair of Plant Physiology, Germany

    Fig. 12: Different phases of field-testing at NCHU Taichung, Taiwan.
    Fig. 12: Different phases of field-testing at NCHU Taichung, Taiwan.

  • Forschungszentrum Jülich, Institut für Bio- und Geowissenschaften, Germany

 

Together with our partners, we established an entire plant-testing pipeline, starting with the generation of transgenic cassava plants, followed by laboratory and greenhouse pre-testing, and ultimately field-testing (Fig. 12).

 

Overview of a young cassava field

 

Overview of an advanced cassava field


Fig. 13: Cassava field-testing at IITA Ibadan, Nigeria.
Fig. 13: Cassava field-testing at IITA Ibadan, Nigeria.

Our field trials are executed together with NCHU Taichung, Taiwan and the IITA Ibadan, Nigeria (Fig. 13).

We test transgenic cassava plants with alterations in source-sink metabolism at both location. IITA Ibadan also does conventional cassava breeding and we work together on different projects characterizing these genotypes.

Our research group and the entire Cassava Source-Sink project hope to contribute towards food security of African smallholder farmers. If you are interested in cassava or would like to support us in any way, feel free to contact wolfgang.zierer@fau.de.

 

Climate Adaptation of Potato – Group Sophia Sonnewald

My research group is mainly interested in the regulation of source – sink interaction during plant development and by adverse environmental conditions, such as heat & drought. We are using mainly potato plants as a model system. Potato plants are among world’s most important crops. Their tubers are an excellent staple food as they are rich in starch and contain minerals, vitamins and essential amino acids. However, potato plants are sensitive to heat and drought and global climate changes are expected to largely affect yield stability and tuber quality.

 

Our current research focuses on two main topics:

  • Understanding responses of potato plants to heat and drought to improve them for the challenges of climate change
  • Molecular analysis of potato tuber development

 

Improving potato plants for the future challenges of climate change

Elevated temperatures affect many physiological and developmental processes in potato plants. Among those are a reduced photosynthetic assimilate production and a strong negative effect on tuber development, starch accumulation and quality.

An important regulator of these processes is the Flowering Locus T homolog SP6A, which is a key tuberization gene. Its gene expression is reduced by heat coinciding with decreased tuber growth. In recent work, we uncovered a small RNA (termed SES) that is strongly induced by elevated temperatures and targets SP6A for post-transcriptional degradation (Lehretz et al. 2019; see Fig. 1).

  • In ongoing work (DFG HotNet; https://gepris.dfg.de/gepris/projekt/432435747) we will further uncover the regulatory network acting under heat stress in potato plants by combining physiological and biochemical with molecular and genetic approaches. We exploit the genetic variability ( 2) to elucidate target genes as we think that there is a great potential to increase yield stability using the available genetic resources. Potato is a complex, highly heterozygous tetraploid crop that renders simple genetic approaches more difficult. Together with the bioinformatics group of Stephan Reinert we perform a detailed phenotyping of various tetraploid cultivars and using a GWAS approach together with transcript profiling experiments identify candidate genes.
  • Within the Horizon 2020 EU funded project Adapt, we aim at a better understanding of responses of potato plants to combined stresses in particular to heat, drought and waterlogging. Apapt is a research consortium of 17 partners from leading academic research institutions, potato breeders, a non-profit EU association, a government agency and a plant phenotyping and imaging technology developer. The objectives are to identify new breeding targets and potato varieties that allow adaptation to changing environmental growth conditions in the future. Amongst others, we will further analyse the role of SP6A and the small regulatory RNA SES. For more information and updates visit the official project’s website (adapt.univie.ac.at) and Twitter account (@eu_Adapt).

  • Changing environmental conditions also lead to reduced tuber starch content and may cause second tuber growth (Fig. 2b, c). Both traits result in loss of tuber quality and hamper their usage. Therefore, my group seeks after elucidating the underlying molecular mechanisms.

 

Molecular analysis of potato tuber development

  • Potato tuber development strongly depends on metabolic and developmental signals from the leaves. Thus, the photoperiodic pathway with Constans / SP6A as key regulators has a strong control over tuber formation and growth. Recent work uncovered that SP6A interacts with sucrose efflux transporter(s) such as Sweet11b and may thereby promote assimilate translocation towards developing tubers. Even though our knowledge increased recently, there are still many open questions about the mode of action and the endogenous and environmental regulators.

 

 

 

Bioanalytics – Group Jörg Hofmann

The Bioanalytics group established a Metabolomics technology platform and a Proteomics platform enabling the qualitative and quantitative analysis of biomolecules. This includes targeted and untargeted metabolite profiling. The Metabolomics branch consists of the following equipment:

Metabolomics platform

LC/MS-MS System

  • ABI/MDS-Sciex QTRAP-3200 (Mass Spectrometer)
  • Dionex ICS-3000 Ion Exchange HPLC (metabolite analysis)
  • Dionex ULTIMATE-3000 HPLC (metabolite analysis)

Other instruments

  • Dionex SUMMIT P680 HPLC (metabolite analysis)
  • Shimadzu GCMS-QP2010S mit GC-2010 (Fatty acid analysis)
  • Äkta Purifier HPLC (Protein purification)
  • Pharmacia P-800 FPLC (low pressure LC)
  • Packard Flow Scintillation Analyser (Radioactive molecules)
  • BIO-TEK ELISA Multiwell microplate photometer (Vis fluorescence)
  • Goebel UVIKON-XL Spectrophotometer (UV/Vis)

Access

Prior to use the analysis platform the requirements of our regulations   (PDF, german)  apply and a sample submission form which is available on request must be filled in and sent via e-mail to:   joerg.hofmann (at) fau.de

The core of our LC-MS/MS system represents the QTrap-3200 which is a versatile hybrid mass spectrometer. It combines the features of three cascaded mass filters (Triple-Quadrupole) needed for precise quantification with the concept of a linear iontrap enabling to derive information about quality (structure determination). This combination cares for an enhanced sensitivity. The Triple-Quadrupole together with other technical features (eg. N2-curtain) allows the analysis of relatively crude samples. For sensitive molecules we can adjust the harshness of ionisation by switching between different ion-sources ( Gas assisted Electro Spray Ionisation (ESI), Atmospheric pressure chemical ionisation (APCI) ). The ion source receives the stream of analytes after separation by the ICS-3000– ion chromatography- or the Ultimate-3000 HPLC system.
The inert ICS-3000 IC is exceptionally suited for ion exchange chromatography e.g. of carbohydrates or phosphorylated intermediates. It generates a “reagent-free” eluent required for mass spectrometry and has additional detectors (conductivity- and 3D amperometry detector) e.g. for the screening of sugars. In combination with the QTrap mass spectrometer we can use this device for targeted metabolite profiling with higher dynamic range and a broad spectrum of compounds.
Combining the Ultimate 3000 HPLC with an UV/Vis Photodiode Array Detector (PDA) results in a sophisticated 3D-visualization of fluorescence signals allowing easy identification and sensitve quantification of e.g. pigments, such as carotenoids or chlorophyll.
We have an additional HPLC system (Dionex SUMMIT) with a fluorescence detector suitable for the sensitive measurement of compounds like tocopherol and (derivatized) amino acids after Reversed Phase (RP) Chromatography.
We are also currently improving methods for GC/MS-based determination of fatty acids.
Our newly installed laboratory is further equipped with various supporting devices. Two types of absorption photometers are used to measure e.g. sugar concentration: 96-well ELISA Plate Readers with washer and fluorescence-detector facilitate quick simultaneous analyses of multiple samples. UV/Vis Spectrophotometers allow more sensitive absorption measurements.
In combination with our Flow Scintillation Analyser after chromatographic separation, we can detect radioactively labeled compounds. Furthermore we have installed a cold lab with an Äkta purifier and a low pressure FPLC sytem for the separation of proteins.
This equipment allows the parallel investigation of metabolites in complex mixtures and supports projects aimed at investigating plant-microbe interactions and primary plant metabolism ( AG S.Sonnewald, AG U.Sonnewald ). Furthermore, plant-cell-to-cell connections (plasmodesmata) are analysed at the biochemical and molecular level.

Proteomics platform

As part of Zentralprojekt Z1 in the Sonderforschungsbereich SFB796 a Proteomics lab was established in 2014. Identification and analysis of proteins and protein complexes with their post-translational modifications can be performed with mass spectrometry instruments.

This platform consists of Ultimate 3000 nano-HPLC and Orbitrap Fusion Tribrid systems designed for proteomic bioanalytics research. Optimized procedures of sample preparation and analysis enable us to work effectively with purified fractions, intact proteins, SDS-PAGE bands/spots, immunoprecipitated proteins (on/off-beads) for the identification of

  •   Interacting partners
  •   PTMs
  •   Differences at protein level (e.g. wild type vs. mutation, transfection, differential expression, stress influence)
  •   Proteome/Secretome studies

Special projects like Biomarker discovery, quantification (labelled/label-free) and phosphoproteome analysis are under development.

Operation and management of the platform is conducted by   Jörg Hofmann

For further details please contact:   joerg.hofmann (at) fau.de ,   uwe.sonnewald (at) fau.de

Sample submission form   to apply for a measurement:
Download this PDF into a file, fill it in, print it into a PDF file again and send it by e-mail.

Biocomputing – Group Stephan Reinert

Figure 1: Circos plot representing the interactions of different omics data sets highlighting the benefit of multi-omics analyses to better dissect abiotic stress resistance.
Figure 1: Circos plot representing the interactions of different omics data sets highlighting the benefit of multi-omics analyses to better dissect abiotic stress resistance.

Food security, consumer preferences, and the imminent threats of the global climate change represent strong forces for breeders to find fast and efficient ways to develop new crop varieties accordingly. As a result, a precise and deep knowledge of abiotic stress resistance and the underlying genetic factors in plants is of utter most importance to find new targets for crop improvement.

The aim of our research is the analysis of different major and minor crop plants to reveal genomic and transcriptomic variations leading to improved crop performance under various stress conditions. To identify these factors we use state-of-the-art statistical and bioinformatic tools from the field of quantitative and population genetics to analyze and integrate diverse data sets such as genomics, transcriptomics, metabolomics, and phenomics. This helps us to disentangle gene regulatory networks and the genetic basis of complex traits and to find new targets for molecular breeding.

Currently, our research focuses on the multi-omics analysis of two important starchy crop plants, cassava (Manihot esculenta) and potato (Solanum tuberosum).

Cassava is a woody shrub that develops starchy underground storage roots and is one of the most important crops for food security, especially in the tropics and subtropics. Although it is the most important staple food for more than 800 million people in the Americas, Africa, and Asia, it is primarily grown by smallholder farmers. Because smallholders have only limited access to the tools of modern agriculture, like heavy farming machinery, pest control or fertilizer, yield increase must come from plants that are inherently more productive, even under conditions of low-input agriculture. Therefore, our research, as a part of the Cassava Source-Sink (CASS)-project, is dedicated in developing robust and yield-improved cassava varieties that will be provided to African smallholder farmers to improve food security in Sub-Saharan Africa.

Potato is one of the most important food crops globally and ranks third only behind the cereals rice and wheat. Due it’s steady increase in overall production it is considered an important staple food source. The modern cultivars originated from the Andes in South America between Bolivia and Peru. Domestication of wild potato dates back nearly 8,000 years. Cultivated potatoes were introduced into Europe in the 1570s and were distributed globally in the late 17th century. Today, potatoes are grown world-wide from latitudes of 65⁰N to 50⁰S and from altitudes of up to 4,000 m. This demonstrates the immense adaptability of potato to many different environmental conditions. Even though potato is well adapted to a variety of environmental conditions, it shows a high sensitivity to abiotic stress conditions such as heat and drought. Especially high temperature (temperatures above 20⁰C) impacts tuber production of potato negatively.

Figure 2: Graphical representation of the quantitative analysis in potato to reveal genomic regions associated with improved performance under abiotic stress conditions.
Figure 2: Graphical representation of the quantitative analysis in potato to reveal genomic regions associated with improved performance under abiotic stress conditions.

Due to the vastly changing climate, increasing global population, and the necessity to produce food even under suboptimal conditions, we are working with national and international partners to improve cassava and potato in three main projects. For details on each project please feel free to contact the PhD student working on the project or out group leader (Stephan Reinert).

 

Unfortunately, conventional cassava breeding is very time-consuming, and it often takes several years before an improved variety can be approved. For this reason, as one of the bioinformatics parts of the CASS project consortium, we are working to complement conventional breeding and use bioinformatics approaches to achieve accelerated research success. For that, we use a wide variety of state-of-the-art methods including RNA (RNAseq) and whole genome sequencing (WGS) data analysis; expression-based genome- and transciptome-wide association studies (GWAS, TWAS, eGWAS); comparative analysis using clustering, association, regression, and dimensionality reduction methods; as well as the integration of phenotypic, metabolomic, and proteomic data. We are especially interested in agronomic, agro-morphological, as well as biotic and abiotic stress traits such as storage root quality, cassava mosaic disease, and cassava green mite severity to name just a few.

In our potato heat tolerance project we are especially interested in the agronomic traits, tuber starch content and tuber yield under heat stress conditions. By performing GWAS on genotype and the agronomic trait data of all potato varieties we will be able to identify candidate genes which are important for heat tolerance. Using these candidate genes in subsequent transcriptome and gene structure analyses we will get a better understanding of the underlying genetic mechanisms and factors for heat tolerance in potato as well as present new targets for molecular breeding to potato breeders.

  • Epigenetics of heat tolerance in potato (Darren Yeo)

During the last decade, it is becoming increasingly clear that agronomic traits of crops such as tuber size and yield are inextricably linked with epigenetic regulation because of environmental stresses. Epigenetic gene regulation refers to the regulation of gene expression by modifying the genome without altering the sequences in the genome. One such epigenetic modification is the methylation and demethylation of cytosines. Methylation patterns may differ among different genotypes, individual plants or even among the tissues and are often associated with environmental stresses including heat stress. This phenomenon could potentially be true for potatoes as well when grown under heat stress. Thus, we aim to profile the methylation patterns among contrasting potato genotypes that are heat-resistant and heat-sensitive grown in order to identify specific methylation regions that potentially regulate gene expression of candidate genes.

 

Figure 3: The Biocomputing Lab from left to right: Koda, Stephan Reinert, Alfred Schmiedl, Darren Yeo, Mohamed Abdrabbou, Alexander Kaier, Sindy Gutschke, Merve Mutlutuerk, Philipp Kleinert, Senta Kryzer, Marina Nedler
Figure 3: The Biocomputing Lab from left to right: Koda, Stephan Reinert, Alfred Schmiedl, Darren Yeo, Mohamed Abdrabbou, Alexander Kaier, Sindy Gutschke, Merve Mutlutuerk, Philipp Kleinert, Senta Kryzer, Marina Nedler

 

 

Yeast Cell Biology – Group Christian Koch

Research of the Fungal Cell Biology group is concerned with the analysis of gene regulation and cell division in the yeast Saccharomyces cerevisiae and with the analysis of phytopathogenic fungi. Using genetic and biochemical techniques, we study transcription factors involved in cell cycle regulation, stress response and gene silencing in yeast. Together with the lab of U. Sonnewald , we study models of compatible plant fungal interactions. Our studies concentrate on the analysis of changes in fungal physiology upon infection and are aimed at identifying fungal genes and effectors involved in the communication with the plant host.

Yeast Cell Biology

Regulated gene expression is not only a vital determinant of differentiation and development, but also important for coordinating events during the cell division cycle. In particular the decision to enter a new cell cycle in late G1-phase is largely determined by regulated transcription of many genes involved in S-phase control. To understand how expression of such genes is regulated, we are studying the regulation, structure and function of the cell cycle regulated transcription factors Swi4, Mbp1 and Swi6. Their timely activation in late G1 is particularly important to control cell size in yeast. Another aspect of our work concerns the identification of other regulators of cell size. We are studying this problem genetically by screening for mutants with altered cell size. In particular, we found the histone deacetylase complex Rpd3/Sin3 to be important for size control in daughter cells. It is becoming increasingly clear that many steps during RNA polymerase II dependent gene expression are coordinated by regulating the physical association of different multienzyme complexes with the polymerase itself. One of the PolII associated protein complexes is the Paf1-Ctr9 complex, which is associated with the elongating polymerase and helps to coordinate several events during the transcription cycle like, histone methylation and also gene silencing. We are studying components of the Paf1 complex and their interactions.

Fungal plant pathogens

We are studying the interaction of the model plant Arabidopsis thaliana with the fungal pathogen Colletotrichum higginsianum. Since, both the host plant and the fungus are genetically tractable this pathosystem is well suited to study the molecular mechanisms of pathology. C. higginsianum belongs to the group of hemibiotrophic fungi which includes some of the economically important crop pathogens like Magnaporthe grisea. Currently, we are using insertional mutagenesis of Colletotrichum higginsianum by Agrobacterium mediated transformation (ATMT) to identify genes required for plant infection. We are particularly interested in the early stages of infection when the pathogen establishes a biotrophic relationship with its host. In another project, we use tagged fungal proteins to analyse the infection process on the cellular level.

Illustration:

Tagged nuclei and plasmamembrane of C. higginsianum, Appressoria of C. higginsianum on plant surface.

Plant-Biochemistry and Biotechnology – Group Uwe Sonnewald

The research group concentrates on application-oriented basic science in the field of plant growth and development as well as aspects of synthetic biology. Plant growth is depended on internal and external factors and it has been proposed that climate change represents the major challenge for food production in the near future. Therefore, we analyze the molecular basis of plant adaptations to periods of heat and drought to make them resilient to climate change. To increase productivity of crop plants such as potato and cassava we use biotechnology to improve assimilate production, allocation and utilization. In synthetic biology we apply targeted protein-protein interactions to reprogram plant metabolism to be better adapted to future climate conditions. One focus of this work is the use of sequence specific, intermolecular isopeptide bridges, which allows the design of artificial protein complexes in in vitro and in plant cells   ( doi: 10.1186/s13007-020-00663-9 ;   doi: 10.1371/journal.pone.0179740 ).

 

Adaptation to climate change:

According to independent climate models, global temperature will increase and distribution of annual rain falls will change. However, little is known about plant responses to combined heat and drought stress. In case of potato a moderate rise in temperature has already profound effects. Potato is the third most important food crop in the world after rice and wheat. Because of its widely distributed cultivation and high yields, it is considered a critical species in terms of food security in face of a growing world population. However, potato is particularly vulnerable to high temperature during various stages of its life cycle. Elevated temperatures strongly suppress tuberisation, negatively affect storage and shelf life of tubers and reduce fitness of seed potatoes. Breeding new heat-stress tolerant cultivars is an urgent need for sustainable increases in potato production, given the negative impact of the rises in temperature due to global warming.

effektekartoffel

To unravel the molecular background of the temperature- and drought-dependent decline in potato yield, different potato varieties are tested within national and international research projects under field and controlled greenhouse conditions. By combining genotyping by sequencing with molecular, biochemical, physiological and agronomical phenotyping yield-relevant genome regions are predicted and validated. This allows a comparison between genotypes and identification of mechanisms which are causally linked to heat- and/or drought-tolerance. Identified processes, genes or alleles can be exploited by conventional breeding and/or biotechnology. Beside this unbiased approach, processes known to be important for yield and resilience are addressed directly. According to current data, elevated temperatures cause a reduction in the expression of the tuber-inducing FT-homologous protein called SP6A (Self-Pruning 6A) and consequently reduced tuber yield ( doi: 10.1111/pce.13366 ). SP6A belongs to the phosphatidylethanolamine-binding proteins (PEBP) and has been shown to inhibit apoplasmic sucrose efflux from the transport phloem by binding and inhibiting activity of SWEET efflux carrier ( doi: 10.1016/j.cub.2019.02.018 ). Inhibition of sucrose efflux supports long distance sucrose transport to developing tubers and has been speculated to be important for tuberization. Ongoing research aims at elucidating the molecular details of SP6A action and regulation. In this context, a small regulatory RNA (SES) could be shown as a novel regulatory of SP6A expression. SES is heat inducible and binds to its target SP6A mRNA. SES binding results in the posttranscriptional degradation of SP6A mRNA and hence inhibition of tuberization ( doi: 10.1016/j.cub.2019.04.027 ). By specifically addressing SP6A or SES expression, potato genotypes with improved stress tolerance can be designed. To achieve this goal breeding and biotechnological approaches including genome editing and transgenesis are applied. Similar to the analysis of heat tolerance, we follow molecular strategies to improve drought tolerance of potato genotypes. These strategies include attempts to reduce water loss by reducing transpiration and approaches to improve water uptake by enhancing root growth. By combining guard cell-specific expression of hexokinase and SP6A expression, transgenic potato plants being more hat and drought tolerant under greenhouse conditions could be generated. These promising results provide the scientific basis for more in-depth studies and hopefully lead to the design of climate adapted potato genotypes.

 

Improving source-sink relations in crop plants:

 

Distribution of photoassimilates, mainly fixed during photosynthesis in source leaves, to harvestable plant organs is the most important determinant of crop yield. Allocation of photoassimilates is affected by environmental and endogenous factors. In several crop plants temperature and day length significantly determine the switch between vegetative and generative growth. In potato for instance, elevated temperatures promote shoot growth and at the same time inhibits tuber-induction, leading to a reduced tuber yield. Similarly, biotic stress often alters source-to-sink relations to support growth of the invading pathogen. This is achieved by reprogramming primary carbon metabolism and leads to a reduced photoassimilate supply of developing sink tissues. Source-to-sink interactions are not static but change during development. In young growing plants the rate of photosynthesis often exceeds sink demand. Thus photoassimilates accumulate in leaves and reduce photosynthetic efficiency (sink inhibition of photosynthesis). After flowering or induction of vegetative sink tissues (such as roots or tubers), this relation shifts and photoassimilate supply to developing sink tissues can get limiting (source limitation). Over the last decades, many factors influencing source-to-sink relations have been deciphered and this knowledge has been used to design transgenic plants with improved biomass production and yield. In frame of two international research projects ( www.photoboost.org ; cass-research.org ) we try to specifically alter the interaction between leaves and storage roots of cassava plants and leaves and tubers of potato plants to increase yield of both crop plants. Here we simultaneously improve leaf (Source) transport (phloem) and root/tuber (Sink) metabolism. The scientific concept of the cassava project has been published in Sonnewald et al., 2020 ( doi: 10.1111/tpj.14865 ). General ideas to improve source-sink relations and crop yield are discussed in Fernie et al., 2020 ( doi: 10.1038/s41477-020-0590-x ).