RWP‐RK domain‐containing transcription factors control cell differentiation during female gametophyte development in Arabidopsis

Abstract

The formation of gametes is a prerequisite for any sexually reproducing organism in order to complete its life cycle. In plants, female gametes are formed in a multicellular tissue, the female gametophyte or embryo sac. Although the events leading to the formation of the female gametophyte have been morphologically characterized, the molecular control of embryo sac development remains elusive. We used single and double mutants as well as cell-specific marker lines to characterize a novel class of gene regulators in Arabidopsis thaliana, the RWP-RK domain-containing (RKD) transcription factors. Morphological and histological analyses were conducted using confocal laser scanning and differential interference contrast microscopy. Gene expression and transcriptome analyses were performed using quantitative reverse transcription-PCR and RNA sequencing, respectively. Our results showed that RKD genes are expressed during distinct stages of embryo sac development. Morphological analysis of the mutants revealed severe distortions in gametophyte polarity and cell differentiation. Transcriptome analysis revealed changes in the expression of several gametophyte-specific gene families (RKD2 and RKD3) and ovule development-specific genes (RKD3), and identified pleiotropic effects on phytohormone pathways (RKD5). Our data provide novel insight into the regulatory control of female gametophyte development. RKDs are involved in the control of cell differentiation and are required for normal gametophytic development.

Autonomous and non‐autonomous functions of the maize Shohai1 gene, encoding a RWP‐RK putative transcription factor, in regulation of embryo and endosperm development

“…Phylogenetic analysis based on the highly conserved RWP‐RK domain indicates that Shai1 is more closely related to RKD5 and therefore unlikely to be an ortholog of RKD4/GRD . While Shai1 has the key function in maize embryogenesis shown in this study, loss‐of‐function rkd5 single mutants do not have a discernible phenotype in Arabidopsis (Tedeschi et al ., ). Maize and Arabidopsis have only one gene in the Shai1 / RKD5 clade (Figure f; Chardin et al ., ; Koi et al ., ; Rövekamp et al ., ).…”

“…In Arabidopsis, loss of function of RKD4/GRD disrupts polarity of the embryo prior to the first mitotic cell division of the zygote (Jeong et al, 2011;Waki et al, 2011). Recently, RKD2, RKD3, RKD4 have been implicated in female gametophyte development (Tedeschi et al, 2017). In contrast, rkd5 single mutants have no discernible phenotype in the embryo or gametophytes (Tedeschi et al, 2017).…”

A transcriptional view on somatic embryogenesis

“…While mutation of RKD4 leads to short suspensors and embryo arrest, induced overexpression of RKD4 in seedlings causes overproliferation of root cells, from which somatic embryos developed. In line with its unique role during early embryogenesis—other RKDs only affect embryo sac development—RKD4 is the only RKD factor that induces SE (Koszegi et al., 2011; Tedeschi, Rizzo, Rutten, Altschmied, & Baumlein, 2017; Waki et al., 2011). …”

OS1 functions in the allocation of nutrients between the endosperm and embryo in maize seeds

“…Phylogenetic analysis of full‐length OS1 homologs from monocotyledonous and dicotyledonous species classified these into two major clades (Figure A; File S2). OS1 was grouped into the RKD clade, along with AtRKD4 and AtRKD5, which are involved in embryo development (Jeong et al ; Waki et al ; Tedeschi et al ) (Figure A).…”

“…Phylogenetic analysis of fulllength OS1 homologs from monocotyledonous and dicotyledonous species classified these into two major clades ( Figure 6A; File S2). OS1 was grouped into the RKD clade, along with AtRKD4 and AtRKD5, which are involved in embryo development (Jeong et al 2011;Waki et al 2011;Tedeschi et al 2017) ( Figure 6A). To investigate the subcellular localization of the protein, we amplified the full-length cDNA of OS1 from the elite inbred maize line B73 and cloned it into a vector containing the green fluorescent protein (GFP) reporter gene and bombarded this construct into onion cells ( Figure 6B, C).…”