Project 7

The role of the transcription factor FLC in growth habit, fruit dimorphism and plant defense of Aethionema arabicum

Supervisors:  Günter Theißen, FSU Jena, Jonathan Gershenzon, MPI for Chemical Ecology, Prof. Dr. Ralf Oelmüller, MPI for Chemical Ecology

Background: The genus Aethiomena has a phylogenetic position at the base of the crucifers (Brassicaceae) and is thus of interest for studying trait evolution in this ecologically and economically important plant family [1]. One of its species, Aethionema arabicum, is an emergent model system of plant eco-evo-devo [1, 2]. While the vast majority of flowering plants develops only a single type of fruits and seeds, Ae. arabicum shows seed and fruit dimorphism: one type of diaspore is a dehiscent fruit with mucilaginous seeds, the other an indehiscent fruit with nonmucilaginous seeds [1]. Fruit dimorphism in Ae. arabicum is interpreted as a blend of bet hedging and developmental plasticity as adaptation to harsh, unpredictably changing habitats [1]. Remarkably, the fraction of dehiscent and indehiscent fruits strongly depends on the growth habit, especially the branching pattern of the plant, which is strongly influenced by physical growth conditions such as light quality and quantity, temperature, and mechanical damage [1, 2]. There is evidence that the plasticity of the fruit morph ratio evolved through the recruitment of a preexisting network governing correlative dominance between shoot organs [2]. The underlying molecular mechanism is complex and involves an interplay between phytohormones, such as auxin and cytokinin, with some transcription factors that control the growth habit, such as BRANCHED1 (BRC1) [2]. The floral repressor FLOWERING LOCUS C (FLC) is among the few classes of seed plant-specific MADS-domain transcription factors that is not conserved in all flowering plants [3]. In crucifers, however, it is involved in the determination of important life history traits, such as the vernalizaton requirement in many Arabidopsis thaliana accessions, and the perennial flowering and thus growth habit of Arabis alpina [4]. QTL analyses suggest that in Ae. arabicum, FLC is involved in the determination of glucosinolate content and hence herbivore defense and plant fitness [5], but nothing is known about other likely roles in plant development and ecology. Unfortunately, that Ae. arabicum is recalcitrant to genetic transformation, e.g. employing floral dip, has until recently hampered its use as a model system.

Project Description: We hypothesize that FLC plays an important role in determination of the growth habit, flowering time, fruit dimorphism and herbivore defense in Ae. arabicum. To test our hypothesis, we will knock-out the FLC gene in Ae. arabicum employing CRISPR/Cas9 and a transformation protocol that has recently been established in our lab. In addition, we will overexpress the FLC gene in conditional and constitutive ways using different kinds of (e.g. inducible and organ-specific) promoters. We will carefully analyze mutant and transgenic plants under different growth conditions with respect to diverse traits such as growth habit, amount of fruit and seed production, fruit dimorphism, and glucosinolate content in different parts of the plant (including the effect on herbivory). Analysis of fruit dimorphism will include carbohydrate and protein analyses of the two kinds of seeds and fruits to estimate their biochemical costs. We will also determine the sequence (incl. promoter) and expression diversity of the FLC gene in different natural accessions of Ae. arabicum and other Aethionema species in order to assess the involvement of the gene in the microevolution of life history traits. All this will tell us a great deal about how FLC helps Ae. arabicum to survive in its extreme habitats. Based on our findings and literature data about FLC orthologues in other crucifer species we will reconstruct the impact of changes at the FLC locus on the evolution of life history traits in the whole of Brassicaceae.
To apply state-of-the art methods we will cooperate with leading scientists during the course of the project, including the co-supervisors at the MPICE and the FSU, and Axel Mithöfer (Department of Bioorganic Chemistry, MPICE), for phytohormone, glucosinolate, carbohydrate and protein analyses.  Ae. arabicum is used already as a model system in a small, but growing group of people with which we have been cooperating [1,2] and will continue to do so. They include Gerhard Leubner (Royal Holloway University of London, UK), M. Eric Schranz (Wageningen University, Netherlands), Ortrun Mittelsten-Scheid (Gregor Mendel Institute, Vienna, Austria), Miroslav Strnad (Palacky University, Olomouc, Czech Republic), Stefan Rensing (University of Marburg, Germany) and Klaus Mummenhoff (University of Osnabrück, Germany).

Candidate profile: We are looking for a candidate with proven skills in molecular biology and a strong interest in plant ecology, development, and evolution. The project involves cooperation between several groups at different locations, hence the ideal candidate has strong communication skills and the ability to cooperate with researchers with different backgrounds (bioinformatics, developmental biology, chemical ecology, evolution). Good time management and organizational skills as well as proficiency in written and spoken English are essential. The candidate should be keen on learning and applying several and diverse state-of-the-art techniques.

References (*from our own lab)

  • Lenser T, et al (2016) Developmental control and plasticity of fruit and seed dimorphism in Aethionema arabicum. Plant Physiol 172, 1691-1707.*
  • Lenser T, et al (2018) When the BRANCHED network bears fruit: how carpic dominance causes fruit dimorphism in Aethionema. Plant J 94, 352-371.*
  • Gramzow L, Theißen G (2015) Phylogenomics reveals surprising sets of essential and dispensable clades of MIKCc-group MADS-box genes in flowering plants. J. Exp.Zool. (Mol. Dev. Evol.) 324B, 353-362.*
  • Kiefer C, et al (2017) Divergence of annual and perennial species in the Brassicaceae and the contribution of cis-acting variation at FLC orthologues. Molecular Ecology 26, 3437-3457.
  • Mohammadin S, et al (2017) Flowering Locus C (FLC) is a potential major regulator of glucosinolate content across developmental stages of Aethionema arabicum (Brassicaceae). Front Plant Sci 8, 876.

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