Abstract
Auxin response factor (ARF) is the key regulator involved in plant development. Despite their physiological importance identified in various woody plants, the functions of ARF genes in longan were still not clear. In this study, 17 longan ARF genes (DlARF) were identified using the reference longan genome data. According to the phylogenetic relationships among longan, Arabidopsis and apple, DlARFs were divided into four classes. Most DlARFs showed a closer relationship with ARFs from apple than those from Arabidopsis. The analysis of gene structure and domain revealed high similarity of different ARF genes in the same class. Typical features of B3-type DNA binding domain (DBD) motif, Auxin Resp motifs, and a highly conserved C-terminal Phox and Bem1 (PB1) domain were present in all DlARFs except for DlARF-2,-3,-13 which lacked PBI domain. Expression profiles of 17 DlARF genes in longan different tissues showed that some DlARF genes were tissues-specific genes. Analysis of three longan transcriptomes showed seven DlARFs (DlARF-1,-2,-6,-8,-9,-11,-16) had higher expression levels during floral bud differentiation of common longan and in the buds of ‘Sijimi’, suggesting these genes may promote floral bud differentiation in longan. Further qPCR analysis showed that among seven DlARF genes, the expression levels of DlARF-2,-6,-11,-16 increased significantly during the physiological differentiation stage of longan floral buds, confirming that they may play a role in flowering induction. Promoter sequence analysis revealed cis-elements related to flowering induction such as low-temperature responsiveness motif and circadian control motif. Motifs linked with hormone response for instance Auxin, MeJA, Gibberellin, and Abscisic acid were also found in promoters. This study provides a comprehensive overview of the ARF gene family in longan. Our findings could provide new insights into the complexity of the regulation of ARFs at the transcription level that may be useful to develop breeding strategies to improve development or promote flowering in longan.
Highlights
Auxin is a vital regulator of plant growth, and plays important roles in diverse aspects of plant development such as control of leaf vascular patterning [1], apical dominance [2], establishment of embryonic axis [3], and root geotropism phototropism of the stem [4], and in fruit development and controlling circadian flower opening and closure [5,6]
Auxin influences developmental processes from embryogenesis to senescence in plants, including that causing apical dominance, controlling embryo development, and promoting the including that causing apical dominance, controlling embryo development, and promoting the floral floral transition [41,42,43]
17 Dimocarpus longan ARF (DlARF) were identified in longan
Summary
Auxin is a vital regulator of plant growth, and plays important roles in diverse aspects of plant development such as control of leaf vascular patterning [1], apical dominance [2], establishment of embryonic axis [3], and root geotropism phototropism of the stem [4], and in fruit development and controlling circadian flower opening and closure [5,6]. Over the past 30 years, it has been clearly certificated that auxins can exert rapid and specific effects on genes at the molecular levels [9] Many gene families, such as auxin/indole-3-acetic acid (Aux/IAA), gretchen hagen 3 (GH3), small auxin-up RNA (SAUR), and auxin response factor (ARF), were involved in auxin signal transduction, forming a complex auxin signal regulation network at the molecular level [10]. In this regulatory pathway, ARF is an important transcription factor family, which DNA binding domain (DBD) can bind to TGTCTC auxin response elements (AuxREs) in the target gene promoter to participate in auxin signal transduction and regulate auxin responsive genes expression [11]. Our results will provide valuable information for understanding the classification and putative functions of DlARFs and make more insight into the molecular basis of auxin responses in longan
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