Quint Lab:Research

broad research scope

HOW do organisms adapt to the environment and how do they react to different biotic and abiotic stimuli?
major players in the conversion of such stimuli into cellular responses are hormones acting as signaling molecules. our lab is primarily interested in understanding the genetics and molecular biology of auxin and other plant hormone responses in the tiny weed arabidopsis thaliana and related brassicaceae. phytohormones are one of the classic fields in plant physiology and the past has shown that understanding hormone action in plants bears great potential for agricultural and horticultural applications. by contributing to the current state of knowledge of hormone biology we hope to participate in the advancement of crop science. since several of these hormone-triggered signaling cascades are regulated by the ubiquitin-proteasome system SCF-type E3 ubiquitin ligases and functional characterization of their selective f-box protein subunits are another focus of our research activities.
we apply mostly genomics approaches, such as:

• forward genetic screens and reverse genetics
• whole genome expression profiling
• utilizing natural genetic variation within the global arabidopsis gene pool
• quantitative genetics → qtl mapping
• evolutionary and population genomics
• comparative genomics
  

natural variation and quantitative genetics of hormone responses

quantitative genetics
we have revealed extensive natural variation for auxin responses in the root in world-wide arabidopsis ecotype collections (see delker et al., Planta 2008). classic genetics tells us that this variation is most likely inherited in a quantitative genetic manner. We are therefore pursuing QTL and association mapping approaches to understand the genetics underlying this variation. Furthermore, we are making an effort to clone selected QTLs with strong effects on auxin-related phenotypes.

population genetics
a possible reason for such natural variation on the physiological level maybe sequence polymorphisms in auxin-associated genes. extensive molecular population genetic analyses allow us to derive selection signatures for the respective gene classes and identify candidate genes which may be the driving forces behind the variation detected.

transcriptional networks

evolutionary insights
from an evolutionary perspective it will be important to learn about the differences in auxin responses on the physiological and the transcriptional level between species. Comparison of inter-species with intra-species variation may shed new light on the evolutionary development of the auxin response pathway(s). We are using closely related brassicaceae species such as thlaspi arvense in this picture for this type of analysis which - in addition to the evolutionary perspective - is most interesting for possible future knowledge transfer to agronomically important species from that family.

TIR1-dependent auxin signaling

to identify novel components of SCF complex regulation and/or auxin signaling we used the f-box protein and auxin receptor mutant tir1-1 for a second site forward genetic screen. in a previous screen in bill gray's lab several enhancers of tir1-1-mediated auxin resistance had been identified (see zhang et al., pnas 2008; ito and gray, plant physiology 2006; quint et al., plant journal 2005; chuang et al., plant cell 2004; gray et al., plant cell 2003). Vice versa, we are screening for suppressors of the root growth defect on auxin-supplemented (2,4-D, artificial auxin) media. we identified appr. 15 independent tir1-1 suppressor (tis) mutants that restored the wild-type response and are currently cloning the underlying gene/s and charactarize the physiological and genetic features of the mutants.

f-box proteins

the evolutionary conserved f-box motifs can be found in various organisms ranging from fungi, insects, fish, and mammals to plants. f-box proteins are subunits of SCF-type E3 ubiquitin ligases and selectively recruit target proteins via their protein-protein interaction domain for ubiquitination and subsequent proteasomal degradation. the arabidopsis genome encodes appr. 700 f-box proteins which makes this gene superfamily one of the largest in eukaryotes. however, a biological function has been assigned to less than 30 genes/proteins of the 700 members. We are generally interested in the evolution and selection patterns acting on f-box proteins (see Schumann et al., 2011 in press) and study a small sub-family to understand the molecular functions of each member.