NEP-TC a rRNA Methyltransferase Involved on Somatic Embryogenesis of Tamarillo (Solanum betaceum Cav.).

Sandra Correia,Célia M Miguel,Paula Veríssimo,Jorge Canhoto,Bruno Casimiro,Margarida Oliveira,Ana T Alhinho

doi:10.3389/fpls.2019.00438

Sandra Correia, Célia M Miguel + Show 5 more

Open Access

https://doi.org/10.3389/fpls.2019.00438

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Abstract

Somatic embryogenesis (SE) is an important biotechnological tool for large-scale clonal propagation and for embryogenesis research. Moreover, genetic transformation and cryopreservation procedures in many species rely on efficient SE protocols. We have been studying different aspects related to SE induction and somatic embryo development in tamarillo (Solanum betaceum Cav.), a small tree from the Solanaceae family. Previous proteomic analyses identified a protein (NEP-TC, 26.5 kDa) consistently present in non-embryogenic calluses of tamarillo, but absent in the embryogenic ones. In this work, the role of NEP-TC during SE was assessed by gene expression analysis and immunolocalization. The results obtained demonstrated that NEP-TC is a putative member of the SpoU rRNA methylase family. This protein, present in the cytoplasm and nucleus, is expressed in non-embryogenic cells and not expressed in embryogenic cells. Slightly enhanced SE induction levels in tamarillo plants with NEP-TC down-regulated levels also supports the role of this protein on SE induction. Heterologous expression was used to confirm NEP-TC rRNA methyltransferase activity, with enhanced activity levels when rRNA was used as a substrate. These data relate a putative member of the SpoU methylase family with plant morphogenesis, in particular with SE induction.

Highlights

Somatic embryogenesis is one of the most useful experimental tools to investigate the morphological, biochemical and physiological events of embryogenesis (Zimmerman, 1993; von Arnold, 2008; Radoeva and Weijers, 2014; De Vries and Weijers, 2017)
To determine the phylogeny of NEP-TC, a protein expressed in non-embryogenic tissues of tamarillo, homologs were retrieved from web-based comparative genomics platforms (Plaza Dicots 3.0) and hand curated, generating a set of 34 known sequences from proteins expressed in other plant and algae species
The results obtained in this work associate a putative member of the SpoU Methylase family protein with the somatic embryogenesis induction process, which is a morphogenic process strongly associated with stress conditions (Zavattieri et al, 2010; Takácet al., 2011), as suggested in tamarillo through the identification of several stressrelated proteins (Correia et al, 2012b)

Summary

Introduction

Somatic embryogenesis is one of the most useful experimental tools to investigate the morphological, biochemical and physiological events of embryogenesis (Zimmerman, 1993; von Arnold, 2008; Radoeva and Weijers, 2014; De Vries and Weijers, 2017). Several molecular markers associated with the embryogenic competence of cells have been reported and reviewed (Yang and Zhang, 2010; Elhiti et al, 2013; Fehér, 2015), including genes related to cell differentiation, morphogenesis, desiccation tolerance, and signal transduction (Radoeva and Weijers, 2014; Zheng and Perry, 2014; Guan et al, 2016; Horstman et al, 2017; Magnani et al, 2017). The majority of the genes causing the embryo-defective mutants were related to housekeeping events (e.g., cell division, cell differentiation, phytohormone response and other indispensable survival processes), and only few embryogenesis-specific genes have been found (Ikeda et al, 2006; Radoeva and Weijers, 2014; Horstman et al, 2017). Many aspects of the embryogenesis program remain to be elucidated

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