Genome-wide identification and expression profiling of auxin response factor (ARF) gene family in maize

Background: Auxin signaling is vital for plant growth and development, and plays important role in apical dominance, tropic response, lateral root formation, vascular differentiation, embryo patterning and shoot elongation. Auxin Response Factors (ARFs) are the transcription factors that regulate the expression of auxin responsive genes. The ARF genes are represented by a large multigene family in plants. The first draft of full maize genome assembly has recently been released, however, to our knowledge, the ARF gene family from maize (ZmARF genes) has not been characterized in detail. Results: In this study, 31 maize (Zea mays L.) genes that encode ARF proteins were identified in maize genome. It was shown that maize ARF genes fall into related sister pairs and chromosomal mapping revealed that duplication of ZmARFs was associated with the chromosomal block duplications. As expected, duplication of some ZmARFs showed a conserved intron/exon structure, whereas some others were more divergent, suggesting the possibility of functional diversification for these genes. Out of these 31 ZmARF genes, 14 possess auxin-responsive element in their promoter region, among which 7 appear to show small or negligible response to exogenous auxin. The 18 ZmARF genes were predicted to be the potential targets of small RNAs. Transgenic analysis revealed that increased miR167 level could cause degradation of transcripts of six potential targets (ZmARF3, 9, 16, 18, 22 and 30). The expressions of maize ARF genes are responsive to exogenous auxin treatment. Dynamic expression patterns of ZmARF genes were observed in different stages of embryo development. Conclusions: Maize ARF gene family is expanded (31 genes) as compared to Arabidopsis (23 genes) and rice (25 genes). The expression of these genes in maize is regulated by auxin and small RNAs. Dynamic expression patterns of ZmARF genes in embryo at different stages were detected which suggest that maize ARF genes may be involved in seed development and germination.