Identification of auxin response factor ARF27 as a regulator of maize root morphogenesis

Auxin is a central phytohormone that mediates root development. This study investigated the genetic basis of auxin-mediated primary root growth in Zea mays (maize) seedlings, which is not well-understood in this key cereal crop. To address this knowledge gap, 618 accessions from the Wisconsin Diversity panel were leveraged for a genome wide association study (GWAS) followed by reverse genetics and in silico gene regulatory network reconstruction (GRN). The GWAS identified several candidate genes associated with variation in root growth responses, including RAMOSA2 and multiple members of the AUXIN RESPONSE FACTOR (ARF) gene family. Maize AUXIN RESPONSE FACTOR27 (ZmARF27), an ortholog of Arabidopsis ARF7 and ARF19, was prioritized for functional characterization. A reduction in ZmARF27 levels led to short primary roots, insensitivity to exogenous auxin, and altered transcriptional responses. Reconstruction of an ZmARF27 GRN included known maize classical root development genes, such as ROOTLESS CONCERNING CROWN ROOTS, numerous auxin pathway genes, and genes associated with cell wall biogenesis. Altogether, this study identifies ZmARF27 as a novel genetic driver of auxin-mediated root growth and gene expression in maize.