Abstract
Key messageExtensive modulation of numerous ARF transcripts in the embryogenic culture of Arabidopsis indicates a substantial role of auxin signaling in the mechanism of somatic embryogenesis induction.Somatic embryogenesis (SE) is induced by auxin in plants and auxin signaling is considered to play a key role in the molecular mechanism that controls the embryogenic transition of plant somatic cells. Accordingly, the expression of AUXIN RESPONSE FACTOR (ARF) genes in embryogenic culture of Arabidopsis was analyzed. The study revealed that 14 of the 22 ARFs were transcribed during SE in Arabidopsis. RT-qPCR analysis indicated that the expression of six ARFs (ARF5, ARF6, ARF8, ARF10, ARF16, and ARF17) was significantly up-regulated, whereas five other genes (ARF1, ARF2, ARF3, ARF11, and ARF18) were substantially down-regulated in the SE-induced explants. The activity of ARFs during SE was also monitored with GFP reporter lines and the ARFs that were expressed in areas of the explants engaged in SE induction were detected. A functional test of ARFs transcribed during SE was performed and the embryogenic potential of the arf mutants and overexpressor lines was evaluated. ARFs with a significantly modulated expression during SE coupled with an impaired embryogenic response of the relevant mutant and/or overexpressor line, including ARF1, ARF2, ARF3, ARF5, ARF6, ARF8, and ARF11 were indicated as possibly being involved in SE induction. The study provides evidence that embryogenic induction strongly depends on ARFs, which are key regulators of the auxin signaling. Some clues on the possible functions of the candidate ARFs, especially ARF5, in the mechanism of embryogenic transition are discussed. The results provide guidelines for further research on the auxin-related functional genomics of SE and the developmental plasticity of somatic cells.
Highlights
The developmental plasticity of plant somatic cells is widely exploited in green biotechnology in the micropropagation and production of transgenic plants
To identify the AUXIN RESPONSE FACTOR (ARF) that are differently expressed during somatic embryogenesis (SE), explant tissues that were induced on various media towards SE, ORG, and seedling development were sampled (Fig. 1)
Using the Arabidopsis cis-regulatory element database (AGRIS; http://arabidopsis.med.ohio-state.edu/AtcisDB/), we found that an Auxin Response Element (AuxRE) is present in the promoters of the majority (60%) of SE-modulated TFs (Gliwicka et al 2013) including the genes that were indicated to have an essential function in embryogenic transition such as LEAFY COTYLEDON (LEC1 and LEC2; Gaj et al 2005), FUSCA3 (FUS3; Ledwoń and Gaj 2011), WUSCHEL (WUS; Zuo et al 2002), BABY BOOM (BBM; Boutilier et al 2002), and MYB115 (Wang et al 2009)
Summary
The developmental plasticity of plant somatic cells is widely exploited in green biotechnology in the micropropagation and production of transgenic plants. Among the regeneration pathways that can be induced in a culture of somatic cells/tissue of plants, the process of somatic embryogenesis (SE) is especially attractive for biotechnology purposes as an efficient and fast system for the clonal propagation of many plant species that are of commercial value (Karami et al 2009). The earliest stage of SE induction attracts the most research attention, because revealing the exo- and endogenous determinants of the embryonic switch contributes to our knowledge of the general mechanism that is involved in developmental cell plasticity and supports the improvement of the plant regeneration systems that are used in biotechnology. A global analysis of SE-transcriptomes indicated that numerous auxin-related genes are transcribed in the embryogenic cultures of different species, including Picea sp. A global analysis of SE-transcriptomes indicated that numerous auxin-related genes are transcribed in the embryogenic cultures of different species, including Picea sp. (van Zyl et al 2003; Stasolla et al 2004), Zea mays (Che et al 2006), Glycine max (Thibaud-Nissen et al 2003), Solanum tuberosum (Sharma et al 2008), and Arabidopsis thaliana (Becker et al 2014)
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