New Regulators of Auxin Response Reveal Insights into Cell Expansion

Tara Ann Enders, Washington University in St. Louis

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Auxin regulates numerous aspects of growth and development. Despite years of studying auxin responses and signaling mechanisms, we still do not understand how many auxin responses are regulated. My thesis research has provided new insights into how auxin regulates growth and development in Arabidopsis. I have revealed the role of MAP KINASE1 (MPK1) in regulated cell-expansion in response to auxin. We hypothesize that MPK1 interacts with ROP BINDING PROTEIN KINASE 1 to regulate the activity of the RHO OF PLANTS small GTPases to regulate cell expansion in an auxin dependent manner. Understanding the role of MPK1 in Arabidopsis will further our understanding of MAPK functions and begin to reveal roles for novel negative regulators of auxin responses. Additionally, I provided some evidence that the proposed auxin receptor AUXIN BINDING PROTEIN 1 (ABP1) may not have the roles in auxin signaling as suggested by previous publications. Identification of a viable Arabidopsis thaliana TILLING mutant defective in the ABP1 auxin binding pocket (abp1-5) allowed inroads into understanding ABP1 function. I found that the abp1-5 line we sequenced contains over 8000 single nucleotide polymorphisms in addition to the ABP1 mutation and that at least some of these mutations may originate from the Arabidopsis Wassilewskija accession. Furthermore, a phyB null allele in the abp1-5 background is likely causative for the long hypocotyl phenotype previously attributed to disrupted ABP1 function.