Members of the Arabidopsis auxin receptor gene family are essential early in embryogenesis and have broadly overlapping functions. Michael J. Prigge, Nikita Kadakia 1 , Kathleen Greenham 2 , and Mark Estelle * Section of Cell and Developmental Biology, University of California San Diego, La Jolla, California 92093-0116 1 Current address: University of California, Riverside, School of Medicine, Riverside, California 2 Current address: Department of Plant and Microbial Biology, University of Minnesota, Saint Paul, Minnesota, 55108 orcid.org/0000-0003-0671-2538 (MJP) orcid.org/0000-0002-1884-1671 (NK) orcid.org/0000-0001-7681-5263 (KG) orcid.org/0000-0002-2613-8652 (ME) ABSTRACT The TIR1/AFB proteins are auxin co-receptors that mediate diverse responses to the plant hormone auxin. The genome of Arabidopsis encodes six TIR1/AFB proteins representing three of the four clades that were established prior to angiosperm radiation. To determine the role of these proteins in plant growth and development we have performed an extensive genetic analysis involving the generation and characterization of all combinations of multiply mutant lines. We find that loss of all six proteins results in defects in embryogenesis as early as the first division of the apical cell. Mutant embryos progress, but exhibit frequent errors in cell division and proliferation of the suspensor. Despite this dramatic phenotype, a single wild-type allele of TIR1 or AFB2 is sufficient to support growth of the plant throughout vegetative certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission. The copyright holder for this preprint (which was not this version posted January 23, 2019. . https://doi.org/10.1101/529248 doi: bioRxiv preprint