Exon junction complex (EJC) core genes play multiple developmental roles in Physalis floridana

Pichang Gong,Jing Li,Chaoying He

doi:10.1007/s11103-018-0795-9

Abstract

Key messageMolecular and functional characterization of four gene families of the Physalis exon junction complex (EJC) core improved our understanding of the evolution and function of EJC core genes in plants.The exon junction complex (EJC) plays significant roles in posttranscriptional regulation of genes in eukaryotes. However, its developmental roles in plants are poorly known. We characterized four EJC core genes from Physalis floridana that were named PFMAGO, PFY14, PFeIF4AIII and PFBTZ. They shared a similar phylogenetic topology and were expressed in all examined organs. PFMAGO, PFY14 and PFeIF4AIII were localized in both the nucleus and cytoplasm while PFBTZ was mainly localized in the cytoplasm. No protein homodimerization was observed, but they could form heterodimers excluding the PFY14-PFBTZ heterodimerization. Virus-induced gene silencing (VIGS) of PFMAGO or PFY14 aborted pollen development and resulted in low plant survival due to a leaf-blight-like phenotype in the shoot apex. Carpel functionality was also impaired in the PFY14 knockdowns, whereas pollen maturation was uniquely affected in PFBTZ-VIGS plants. Once PFeIF4AIII was strongly downregulated, plant survival was reduced via a decomposing root collar after flowering and Chinese lantern morphology was distorted. The expression of Physalis orthologous genes in the DYT1-TDF1-AMS-bHLH91 regulatory cascade that is associated with pollen maturation was significantly downregulated in PFMAGO-, PFY14- and PFBTZ-VIGS flowers. Intron-retention in the transcripts of P. floridana dysfunctional tapetum1 (PFDYT1) occurred in these mutated flowers. Additionally, the expression level of WRKY genes in defense-related pathways in the shoot apex of PFMAGO- or PFY14-VIGS plants and in the root collar of PFeIF4AIII-VIGS plants was significantly downregulated. Taken together, the Physalis EJC core genes play multiple roles including a conserved role in male fertility and newly discovered roles in Chinese lantern development, carpel functionality and defense-related processes. These data increase our understanding of the evolution and functions of EJC core genes in plants.

Highlights

The exon junction complex (EJC) is a vital surveillance system in posttranscriptional regulation of mRNAs in eukaryotes, including pre-mRNA splicing, matured mRNA transport, non-sense mediated mRNA decay (NMD) and protein translation enhancement (Tang et al 2004; Moore 2005; Ashton-Beaucage et al 2010; Roignant and Treisman 2010; Ghosh et al 2012; Kervestin and Jacobson 2012; Chazal et al 2013; Le Hir et al 2016)
We found that PFMAGO1 (Fig. 3a–c), PFMAGO2 (Fig. 3d–f), PFY14 (Fig. 3g–i), and PFeIF4AIII (Fig. 3j–l) shared a similar distribution in that they might be localized both in the nucleus and cytoplasm
We found that the root collar area was rotten in these dead PFeIF4AIII-Virus-induced gene silencing (VIGS) plants compared to the negative control (NC) plants (Fig. 6e, f). Quantitative RT-PCR (qRT-PCR) results indicated that PFeIF4AIII expression in the root collar of these PFeIF4AIII-VIGS plants was severely downregulated (P < 0.01, defined as VIGS-I), while, in the PFeIF4AIII-VIGS plants that showed normal phenotypes, the gene expression was not altered compared to the wild type (WT) and NC plants (Fig. 6g)

Summary

Introduction

The exon junction complex (EJC) is a vital surveillance system in posttranscriptional regulation of mRNAs in eukaryotes, including pre-mRNA splicing, matured mRNA transport, non-sense mediated mRNA decay (NMD) and protein translation enhancement (Tang et al 2004; Moore 2005; Ashton-Beaucage et al 2010; Roignant and Treisman 2010; Ghosh et al 2012; Kervestin and Jacobson 2012; Chazal et al 2013; Le Hir et al 2016). The EJC core consists of four proteins, including MAGOH NASHI (MAGO), RNA-binding motif 8A (RBM8A, known as Y14), eukaryotic initiation factor 4A3 (eIF4AIII or eIF4A3) and metastatic lymph node 51 (MLN51/CASC3) in mammals or Barentsz (BTZ) in Drosophila (Ballut et al 2005; Tange et al 2005) These four proteins form intertwined interaction networks by stably clamping mRNA molecules in a sequence-independent manner during the posttranscriptional regulation process (Andersen et al 2006; Bono et al 2006). Knockdown of either EJC core component genes causes widespread and similar alternative splicing changes in mammalian cells (Wang et al 2014)

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