AUTHOR=Kim Sun Ho , Bahk Sunghwa , An Jonguk , Hussain Shah , Nguyen Nhan Thi , Do Huy Loc , Kim Jae-Yean , Hong Jong Chan , Chung Woo Sik 

TITLE=A Gain-of-Function Mutant of IAA15 Inhibits Lateral Root Development by Transcriptional Repression of LBD Genes in Arabidopsis

JOURNAL=Frontiers in Plant Science

VOLUME=11

YEAR=2020

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2020.01239

DOI=10.3389/fpls.2020.01239

ISSN=1664-462X

ABSTRACT=<p>Lateral root development is known to be regulated by Aux/IAA-ARF modules in <italic>Arabidopsis</italic><italic>thaliana</italic>. As components, several Aux/IAAs have participated in these Aux/IAA-ARF modules. In this study, to identify the biological function of IAA15 in plant developments, transgenic plant overexpressing the gain-of-function mutant of IAA15 (IAA15<sup>P75S</sup> OX) under the control of dexamethasone (DEX) inducible promoter, in which IAA15 protein was mutated by changing Pro-75 residue to Ser at the degron motif in conserved domain II, was constructed. As a result, we found that IAA15<sup>P75S</sup> OX plants show a decreased number of lateral roots. Coincidently, <italic>IAA15</italic> promoter-GUS reporter analysis revealed that <italic>IAA15</italic> transcripts were highly detected in all stages of developing lateral root tissues. It was also verified that the IAA15<sup>P75S</sup> protein is strongly stabilized against proteasome-mediated protein degradation by inhibiting its poly-ubiquitination, resulting in the transcriptional repression of auxin-responsive genes. In particular, transcript levels of <italic>LBD16</italic> and <italic>LBD29</italic>, which are positive regulators of lateral root formation, dramatically repressed in IAA15<sup>P75S</sup> OX plants. Furthermore, it was elucidated that IAA15 interacts with ARF7 and ARF19 and binds to the promoters of <italic>LBD16</italic> and <italic>LBD29</italic>, strongly suggesting that IAA15 represses lateral root formation through the transcriptional suppression of <italic>LBD16</italic> and <italic>LBD29</italic> by inhibiting ARF7 and ARF19 activity. Taken together, this study suggests that IAA15 also plays a key negative role in lateral root formation as a component of Aux/IAA-ARF modules.</p>