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 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.
natural variation and quantitative genetics of hormone responses
we have revealed extensive natural variation for auxin responses in the root in world-wide arabidopsis ecotype collections (delker et al., planta 2008) and could recently determine the first quantitative trait loci (QTLs) involved in the inheritance of this genetic variation. the question that arises is which genes are underlying the QTLs and what are the allelic variants responsible for the variation? to address these questions we are fine-mapping the target intervals and make use of the vast genetic resources of arabidopsis thaliana to come up with a reasonable number of candidate genes that can be tested for their ability to functionally complement the differences in auxin response. we have observed that ecotypes with a high degree of auxin insensitivity in the root do not necessarily display the same insensitivity in other organs like the hypocotyl. hence, it is likely that the various factors responsible for this variation are downstream components and also look at transcriptional differences in response to auxin between ecotypes.