A Synthetic Approach Allows Rapid Characterization of the Maize Nuclear Auxin Response Circuit

Abstract

Auxin plays a key role across all land plants in growth and developmental processes. Although auxin signaling function has diverged and expanded, differences in the molecular functions of signaling components have largely been characterized in Arabidopsis (Arabidopsis thaliana). Here, we used the nuclear Auxin Response Circuit recapitulated in yeast (Saccharomyces cerevisiae) system to functionally annotate maize (Zea mays) auxin signaling components, focusing on genes expressed during the development of ear and tassel inflorescences. All 16 maize auxin/indole-3-acetic acid repressor proteins were degraded in response to auxin with rates that depended on both receptor and repressor identities. When fused to the maize TOPLESS homolog RAMOSA1 ENHANCER LOCUS2, maize auxin/indole-3-acetic acids were able to repress AUXIN RESPONSE FACTOR transcriptional activity. A complete auxin response circuit comprising all maize components, including the ZmAFB2/3 b1 maize AUXIN SIGNALING F-BOX (AFB) receptor, was fully functional. The ZmAFB2/3 b1 auxin receptor was more sensitive to hormone than AtAFB2 and allowed for rapid circuit activation upon auxin addition. These results validate the conserved role of predicted auxin response genes in maize as well as provide evidence that a synthetic approach can facilitate broader comparative studies across the wide range of species with sequenced genomes.

Improving architectural traits of maize inflorescences

“…While auxin-related mutants affect suppressed bract and axillary meristem initiation as well as inflorescence meristem size, presumably through a feedback mechanism (Shi et al 2018 ), these processes are inherently linked and it is yet unclear whether specific manipulations of auxin signaling in inflorescences may yield to practical bioengineering approaches. It is nonetheless conceivable that modulation of auxin response by engineering stability variants of AUX/IAA proteins (Ramos Baez et al 2020 ) may alter the patterning of lateral organ primordia and consequently axillary meristems in inflorescence meristems, producing desirable architectural changes in maize inflorescences. Similar approaches have been indeed successfully used in Arabidopsis , where different mutations in IAA28 that alter auxin-driven degradation rates were shown to affect phyllotaxy (Moss et al 2015 ).…”

Dynamic context-dependent regulation of auxin feedback signaling in synthetic gene circuits

“…Given previous indications of inadequate repression by Aux-IAA repressors alone in yeast ( 12 , 16 ), likely due to suboptimal Histone deacetylase (HDAC) recruitment ( 17 ), we engineered an active repressor synthetic BODENLOS (sBDL) by fusing the yeast repression domain from the SSN6 repressor ( 18 ) to BDL. SSN6 interacts with TUP1 ( 19 ), akin to plant TPL that interacts with BDL ( 20 ).…”

Experimental evolution in maize with replicated divergent selection identifies plant-height associated SNPs

“…The plant height candidate gene iAA8 is located within the putatively selected region from 9.437 to 10.457 Mb on chromosome 3 (Ramos Báez et al, 2020). The plant height gene Dwarf1 is also located in this region (Teng et al, 2013;Peiffer et al, 2014;Liu, Fernie and Yan, 2020).…”

“…The iAA8 gene was also observed to regulate maize inflorescence architecture (Galli et al, 2015;Ramos Báez et al, 2020). Both genes appear to be causal for plant height differences based on the literature (Teng et al, 2013;Peiffer et al, 2014;Liu, Fernie and Yan, 2020;Ramos Báez et al, 2020). Therefore, these candidate genes were used as ground truth to test the method.…”