Genome-wide characterization of auxin response factor (ARF) genes in bermudagrass and ectopically functional analysis of CdARF6-B2 gene in Arabidopsis

Auxin response factors (ARFs) are important transcription factors that regulate the expression of auxin response genes, thus play crucial roles in plant growth and development. However, the functions of ARF genes in bermudagrass (Cynodon dactylon L.), a turfgrass species of great economic value, remain poorly understood. In this study, a total of 86 CdARF genes were identified from the C. dactylon genome and were categorized into five groups according to their phylogenetic relationships. The five groups of CdARF genes exhibited specific gene structure and protein domain characteristics, and showed distinct gene expression patterns in different organs, wild accessions and under different stress treatments. Among the 86 CdARF genes, the CdARF6-B2 gene encoded an N-terminally truncated group V ARF protein with high sequence similarity to AtARF2 and OsARF24. The CdARF6-B2 gene was highly expressed in the aboveground vegetative organs (leaf, shoot and stolon) and weakly expressed in the root. The CdARF6-B2 protein was localized in the nucleus but showed no transactivation activity, although its middle region had a strong transactivation activity. Ectopic expression of CdARF6-B2 inhibited the vegetative growth of transgenic Arabidopsis plants possibly through down-regulating the expression of auxin transport-related PIN3 gene and impeding the polar transport of auxin. These results not only established solid foundations to characterize the regulatory mechanism of auxin signaling in the growth and development of bermudagrass but also provided new insights into the function of ARF genes in plants.