Abstract
Explaining how the small molecule auxin triggers diverse yet specific responses is a long-standing challenge in plant biology. An essential step in auxin response is the degradation of Auxin/Indole-3-Acetic Acid (Aux/IAA, referred to hereafter as IAA) repressor proteins through interaction with auxin receptors. To systematically characterize diversity in degradation behaviors among IAA|receptor pairs, we engineered auxin-induced degradation of plant IAA proteins in yeast (Saccharomyces cerevisiae). We found that IAA degradation dynamics vary widely, depending on which receptor is present, and are not encoded solely by the degron-containing domain II. To facilitate this and future studies, we identified a mathematical model able to quantitatively describe IAA degradation behavior in a single parameter. Together, our results demonstrate the remarkable tunability conferred by specific configurations of the auxin response pathway.
Highlights
Explaining how the small molecule auxin triggers diverse yet specific responses is a long-standing challenge in plant biology
Our engineered auxin response system consisted of pairwise matings of yeast expressing either yellow fluorescent protein (YFP)-IAA fusion proteins or AUXIN SIGNALING F-BOX PROTEINS (AFBs) (Fig. 1A)
In contrast to the “basal degradation” rates observed in plants (Dreher et al, 2006), YFP-IAA proteins were essentially stable in yeast in the absence of auxin or a functional AFB
Summary
Explaining how the small molecule auxin triggers diverse yet specific responses is a long-standing challenge in plant biology. To systematically characterize diversity in degradation behaviors among IAA|receptor pairs, we engineered auxin-induced degradation of plant IAA proteins in yeast (Saccharomyces cerevisiae). A range of auxin-associated phenotypes, including profound disruptions in development and severely compromised responses to environmental signals, are caused by single amino acid substitutions that stabilize transcriptional corepressor proteins called the Auxin/Indole-3Acetic Acids (Aux/IAAs, referred to hereafter as IAAs; Chapman and Estelle, 2009). The diversity of these phenotypes and the size of the IAA family suggest that IAAs may provide specificity in auxin responses (Lokerse and Weijers, 2009). The synthetic toolkit described here will facilitate rapid testing of hypotheses about the ubiquitylation of IAA proteins and suggests a means to characterize other hormone-induced protein degradation pathways
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