Group Sophia Sonnewald



Molecular Physiology / Transcriptomics

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 (or pathogen infection). We are using mainly potato plants as a model system. Potato is among the 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 expression is reduced by heat coinciding with decreased tuber growth. We discovered a small RNA (termed SES) that is strongly induced by elevated temperatures and targets SP6A for post-transcriptional degradation (Lehretz et al. 2019; see Figure 1).

Figure 1: Schematic representation of effects of elevated temperatures on potato plant metabolism and development. Photosynthetic carbon production and allocation is inhibited. Transcript accumulation of the key tuberisation gene SP6A is decreased by a heat-induced small RNA (named SES). Together with the induction of thermomorphogenis and other effects this results in inhibiton of tuber development and/or reduced starch accumulation.


In ongoing work (DFG HotNet) we will further unravel the regulatory network acting under heat stress in potato plants by combining physiology and biochemistry with molecular and genetic approaches. We exploit the genetic variability (Figure 2) to elucidate target genes as we think that there is a great potential to increase yield stability within the available genetic resources. The potato is a complex highly heterozygous tetraploid crop that renders simple genetic approaches more difficult. Together with the bioinformatics group of José M. Corral García we perform a detailed phenotyping of various tetraploid cultivars and using a GWAS approach together with transcript profiling experiments identify candidate genes.

Figure 2: Responses to heat stress differ in potato genotypes. Elevated temperatures induce stronger thermomorphogenesis (A), more dramatic decrease in tuber starch content (B) and more frequent appearance of 2nd tuber growth (C) in susceptible cultivars than in tolerant ones.


Within the Horizon 2020 EU funded project Adapt, we aim to gain a better understanding of responses of potato plants to combined stresses in particular to heat, drought and waterlogging. Adapt is a research consortium of 17 partners from leading academic research institutions, potato breeders, a non-profit EU association, a government agency and a developer of screening technology. The objectives are to identify new breeding targets and potato varieties that allow adaptation to changing environmental growth conditions of 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 ( 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 to elucidate 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.
We are currently performing molecular and biochemical analyses to (i) unravel role of the blue light receptor FKF1 in the regulation of tuber development and (ii) to obtain a better understanding how SP6A alters assimilate allocation and source-sink relations.