An auxin response factor regulates tiller angle and shoot gravitropism by directly activating related gene expression in rice

Introduction

The angle of tillers is crucial for shaping plant architecture, which in turn affects grain yield of rice. The formation of tiller angle is associated with the asymmetrical distribution and polar transport of auxin. However, the roles of auxin signaling in regulating tiller angle in rice remain unclear.

Objective

This study identifies Oryza sativa Auxin Response Factor 5 (OsARF5) as a key regulator of tiller angle development in rice.

Methods

The osarf5-1 mutant was obtained through using chemical mutagenesis. The differentially expressed genes were identified through quantitative RT-PCR and high-throughput mRNA sequencing. The interactions between OsARF5 protein and its targeted-DNAs was analyzed by chromatin immunoprecipitation and dual-luciferase reporter assays. Protein-protein interactions were assessed using yeast two-hybrid and bimolecular fluorescence complementation methods.

Results

The osarf5-1 mutation enlarges the tiller angle, weakens shoot gravitropism, and diminishes the response to auxin in rice. OsARF5 binds to the cis-acting elements in the promoters of genes related to tiller angle development and activates their expression. Genome-wide studies identify thousands of differentially expressed genes (DEGs), including auxin response genes, between wild-type and osarf5-1. Under gravistimulation, the number of DEGs in osarf5-1 decreases, indicating the involvement of OsARF5 in shoot gravitropism. The OsARF5 physically interact with three rice Indole Acetic Acid (OsIAA) repressors, forming complexes that facilitate their functions. Mutations in OsIAAs lead to a more compact plant architecture, and the expression of OsARF5-target genes is elevated in osiaa mutants, suggesting that the OsIAAs counteract OsARF5′s effects on tiller angle control.

Conclusion

OsARF5 is associated with three OsIAAs to bind to the promoter of the target genes, regulating their expression to modulate shoot gravitropism and tiller angle in rice. These findings offer new insights into the principles governing tiller angle control in rice.