TURAN and EVAN Mediate Pollen Tube Reception in Arabidopsis Synergids through Protein Glycosylation

Abstract

Pollen tube (PT) reception in flowering plants describes the crosstalk between the male and female gametophytes upon PT arrival at the synergid cells of the ovule. It leads to PT growth arrest, rupture, and sperm cell release, and is thus essential to ensure double fertilization. Here, we describe TURAN (TUN) and EVAN (EVN), two novel members of the PT reception pathway that is mediated by the FERONIA (FER) receptor-like kinase (RLK). Like fer, mutations in these two genes lead to PT overgrowth inside the female gametophyte (FG) without PT rupture. Mapping by next-generation sequencing, cytological analysis of reporter genes, and biochemical assays of glycoproteins in RNAi knockdown mutants revealed both genes to be involved in protein N-glycosylation in the endoplasmic reticulum (ER). TUN encodes a uridine diphosphate (UDP)-glycosyltransferase superfamily protein and EVN a dolichol kinase. In addition to their common role during PT reception in the synergids, both genes have distinct functions in the pollen: whereas EVN is essential for pollen development, TUN is required for PT growth and integrity by affecting the stability of the pollen-specific FER homologs ANXUR1 (ANX1) and ANX2. ANX1- and ANX2-YFP reporters are not expressed in tun pollen grains, but ANX1-YFP is degraded via the ER-associated degradation (ERAD) pathway, likely underlying the anx1/2-like premature PT rupture phenotype of tun mutants. Thus, as in animal sperm–egg interactions, protein glycosylation is essential for the interaction between the female and male gametophytes during PT reception to ensure fertilization and successful reproduction.

The Molecular Dialog between Flowering Plant Reproductive Partners Defined by SNP-Informed RNA-Sequencing

“…consequence of highly coordinated cell-cell signaling requiring pollen tube and synergid transcriptional networks (Leydon et al, 2013;Liang et al, 2013;Mendes et al, 2016), expression of cell surface signaling molecules (Escobar-Restrepo et al, 2007;Kessler et al, 2010;Lindner et al, 2015;Liu et al, 2016), and Ca 2+ fluxes that define which of two synergids receives the pollen tube (Denninger et al, 2014;Ngo et al, 2014). Using SNP-informed RNA-seq analysis of myb triple mutant compared with wild-type pollinations, we have provided a comprehensive set of genes expressed by pollen tubes that mediate interactions with female cells required for pollen tube burst, sperm release and synergid degeneration.…”

The Role of LORELEI in Pollen Tube Reception at the Interface of the Synergid Cell and Pollen Tube Requires the Modified Eight-Cysteine Motif and the Receptor-Like Kinase FERONIA

“…The fer female gametophyte fails to induce pollen tube reception and consequently remains unfertilized (Huck et al, 2003;Escobar-Restrepo et al, 2007;Haruta et al, 2014). Many mutants cause a similar phenotype due to defects in the female gametophyte: these include scylla (syl), lorelei (lre), nortia (nta), evan, and turan (Capron et al, 2008;Rotman et al, 2008;Kessler et al, 2010;Tsukamoto et al, 2010;Lindner et al, 2015). Of these, the identity of SYL remains unknown.…”

“…LRE and NTA function with FER in pollen tube reception (Kessler et al, 2010;Duan et al, 2014;Li et al, 2015; also see below). TURAN and EVAN may N-glycosylate synergidexpressed proteins that are involved in pollen tube reception (Lindner et al, 2015). Also, maize (Zea mays) EMBRYO SAC4 induces pollen tube burst via opening of the potassium channel KZM1 in the pollen tube (Amien et al, 2010).…”

“…Consistent with the prediction that the GPI anchors LRE to the membrane, transiently expressed GFP-LRE localized to the surface of Arabidopsis mesophyll protoplasts (Capron et al, 2008) and citrine yellow fluorescent protein (cYFP)-LRE localized to the FA (Lindner et al, 2015). However, whether the predicted GPI anchor addition domains in LRE are important for its function in pollen tube reception has not been experimentally tested.…”

POLYPRENOL REDUCTASE2 Deficiency Is Lethal in Arabidopsis Due to Male Sterility

“…Moreover, Dol deficiency might disturb the function of COBL10, a GPI-anchored protein that is a component of pollen tube internal machinery critical for normal pollen tube growth and directional sensing in the female transmitting tract (Li et al, 2013). In line with this, an essential role of Dol kinase (DOK) in pollen development and the pollen tube reception pathway (Lindner et al, 2015) has been described recently.…”