# Genome-Wide Identification of GmARF9b/GmARF2a Negatively Regulate Root Growth in Soybean

## TL;DR

This study identifies two soybean genes, GmARF9b and GmARF2a, that negatively regulate root growth, offering insights into plant root development and potential applications in agriculture.

## Contribution

The study identifies and functionally characterizes two soybean ARF repressor genes involved in root growth regulation.

## Key findings

- Two GmARF genes, GmARF9b and GmARF2a, were identified as repressors of root growth in soybean.
- Overexpression of GmARF9b and GmARF2a inhibited root growth and altered root cell structure.
- The genes are primarily expressed in root tissues and localized in the nucleus.

## Abstract

Auxin is the most important phytohormone, regulating root growth and development in plants. ARFs function as central regulators in auxin signaling in model plants, and the functions of ARF activators have been widely investigated, while the functions of ARF repressors remain elusive. In this study, we investigated the family of GmARFs in soybean through a genome-wide expression pattern and functional study of roots highly expressing ARFs. In total, we identified 59 GmARF members in the soybean genome. GmARFs harbor canonical B3 DNA-binding (B3), ARF (Aux rep), and PB1 functional protein domains. We identified two potential repressor genes, GmARF9b (Glyma.03G070500) and GmARF2a (Glyma.05G200800), which are specifically or highly expressed in the roots. Histochemical staining suggested that both genes are primarily expressed in the stele, root tips, and lateral root primordia. Subcellular localization analysis showed they were mainly localized in the nucleus. Overexpression of GmARF9b and GmARF2a significantly inhibited root growth using a transgenic hairy root assay. Root section analysis further suggested that GmARF9b and GmARF2a negatively regulated cortical cell layers and the longitudinal cell length of roots, thereby modulating root growth. Overall, this study has preliminarily identified two GmARFs that inhibit root growth in soybean. This discovery has deepened our understanding of the functions of ARFs in root development and has provided guidance for breeding crop roots with improved nutrient use efficiency.