Endogenous target mimics down-regulate miR160 mediation of ARF10, -16, and -17 cleavage during somatic embryogenesis in Dimocarpus longan Lour

Abstract

MicroRNA160 plays a critical role in plant development by negatively regulating the auxin response factors ARF10, -16, and -17. However, the ways in which miR160 expression is regulated at the transcriptional level, and how miR160 interacts with its targets during plant embryo development, remain unknown. Here, we studied the regulatory relationships among endogenous target mimics (eTMs), and miR160 and its targets, and their involvement in hormone signaling and somatic embryogenesis (SE) in Dimocarpus longan. We identified miR160 family members and isolated the miR160 precursor, primary transcript, and promoter. The promoter contained cis-acting elements responsive to stimuli such as light, abscisic acid, salicylic acid (SA) and heat stress. The pri-miR160 was down-regulated in response to SA but up-regulated by gibberellic acid, ethylene, and methyl jasmonate treatment, suggesting that pri-miR160 was associated with hormone transduction. Dlo-miR160a, -a∗ and -d∗ reached expression peaks in torpedo-shaped embryos, globular embryos and cotyledonary embryos, respectively, but were barely detectable in friable-embryogenic callus. This suggests that they have expression-related and functional diversity, especially during the middle and later developmental stages of SE. Four potential eTMs for miR160 were identified. Two of them, glucan endo-1,3-beta- glucosidase-like protein 2-like and calpain-type cysteine protease DEK1, were confirmed to control the corresponding dlo-miR160a∗ expression level. This suggests that they may function to abolish the binding between dlo-miR160a∗ and its targets. These two eTMs also participated in 2,4-D and ABA signal transduction. DlARF10, -16, and -17 targeting by dlo-miR160a was confirmed; their expression levels were higher in friable-embryogenic callus and incomplete compact pro-embryogenic cultures and responded to 2,4-D, suggesting they may play a major role in the early stages of longan SE dependent on 2,4-D. The eTMs, miR160, and ARF10, -16, and -17 exhibited tissue specificity in ‘Sijimi’ longan vegetative and reproductive organs, but were not significant negatively correlated. These results provide insights into the possible role of the eTM-miR160-ARF10-16-17 pathway in longan somatic embryo development.

Epigenetic Regulation of Auxin-Induced Somatic Embryogenesis in Plants

“…The auxin-related miRNAs frequently target the fundamental components of the auxin signaling pathway, including the ARFs, which are involved in SE induction [27,93]. Accordingly, insights into embryogenic cultures of Arabidopsis and other plants indicated that miR160 could directly regulate the expression of ARF10, ARF16, and ARF17; miR167 seems to the control expression of ARF6 and ARF8, while miR390 possibly downregulates the ARF2, ARF3, ARF4 transcripts [55,63,64,68,81,85,86].…”

Dynamic Transcriptome Analysis Reveals Uncharacterized Complex Regulatory Pathway Underlying Dose IBA-Induced Embryogenic Redifferentiation in Cotton

“…ARF4 and AUX22B genes were selected from the plant hormone signal transduction pathway, which are the two key transcription factors involved in regulating the expression of auxin-responsive genes. Auxin response factor (ARFs) is considered as essential SE genes that are specifically activated during embryogenic differentiation [31][32][33][34]. ARFs bind auxin response promoter elements, mediate transcriptional responses to auxin and regulate auxin-mediated transcriptional activation/repression, together with Aux/IAA [35,36].…”

MicroRNAs Are Intensively Regulated during Induction of Somatic Embryogenesis in Arabidopsis

“…Similar to the widely documented involvement of miRNA molecules in plant development in vivo (Jin et al, 2013), the expression of miRNAs was reported during in vitro induced SE in several plant species including Citrus sinensis, Dimocarpus longan, Gossypium hirsutum, Larix kaempferi, Larix leptolepis, Liriodendron tulipifera × L. chinense, Manihot esculenta , and Zea mays (Zhang et al, 2012, 2014; Li et al, 2013; Lin and Lai, 2013; Yang et al, 2013; Chávez-Hernández et al, 2015; Wu et al, 2015; Lin et al, 2015a,b; Khatabi et al, 2016). Thus, the engagement of miRNAs in the embryogenic transition that is induced in vitro is assumed, although knowledge about the function of the specific miRNA in SE induction is very limited.…”