RWP-RK Domain 3 (OsRKD3) induces somatic embryogenesis in black rice

Abstract

Background Plants have the unique capability to form embryos from both gametes and somatic cells, with the latter process known as somatic embryogenesis. Somatic embryogenesis (SE) can be induced by exposing plant tissues to exogenous growth regulators or by the ectopic activation of embryogenic transcription factors. Recent studies have revealed that a discrete group of RWP-RK DOMAIN-CONTAINING PROTEIN (RKD) transcription factors act as key regulators of germ cell differentiation and embryo development in land plants. The ectopic overexpression of reproductive RKDs is associated with increased cellular proliferation and the formation of somatic embryo-like structures that bypass the need for exogenous growth regulators. However, the precise molecular mechanisms implicated in the induction of somatic embryogenesis by RKD transcription factors remains unknown. Results In silico analyses have identified a rice RWP-RK transcription factor, named Oryza sativa RKD3 (OsRKD3), which is closely related to Arabidopsis thaliana RKD4 (AtRKD4) and Marchantia polymorpha RKD (MpRKD) proteins. Our study demonstrates that the ectopic overexpression of OsRKD3, which is expressed preferentially in reproductive tissues, can trigger the formation of somatic embryos in an Indonesian black rice landrace (Cempo Ireng) that is normally resistant to somatic embryogenesis. By analyzing the transcriptome of induced tissue, we identified 5,991 genes that exhibit differential expression in response to OsRKD3 induction. Among these genes, 50% were up-regulated while the other half were down-regulated. Notably, approximately 37.5% of the up-regulated genes contained a sequence motif in their promoter region, which was also observed in RKD targets from Arabidopsis. Furthermore, OsRKD3 was shown to mediate the transcriptional activation of a discrete gene network, which includes several transcription factors such as APETALA 2-like (AP2-like)/ETHYLENE RESPONSE FACTOR (ERF), MYB and CONSTANS-like (COL), and chromatin remodeling factors associated with hormone signal transduction, stress responses and post-embryonic pathways. Conclusions Our data show that OsRKD3 modulates an extensive gene network and its activation is associated with the initiation of a somatic embryonic program that facilitates genetic transformation in black rice. These findings hold substantial promise for improving crop productivity and advancing agricultural practices in black rice.

Genome-Wide Identification and Characterization of the RWP-RK Proteins in Zanthoxylum armatum

“…In this mechanism, the fertilization step is skipped, allowing cells from nucellus or integument tissues to develop into somatic embryos. Previous studies have highlighted the crucial role of RWP-RK transcription factors in both somatic embryogenesis and apomixis processes [17,18,23]. Therefore, investigating the expression pattern of the ZaRWP-RK transcription factors during the apomictic reproduction process in Z. armatum is of great importance.…”

“…Previous research has demonstrated that citrus apomixis may be caused by the expression of a gene known as CitRWP (Cg4g018970), which encodes a protein with an RWP-PK domain [16]. Similarly, OsRKD3 can regulate somatic embryogenesis in black rice [18]. According to the results of the phylogenetic tree analysis, four genes (ZaRKD2,…”

“…Previous research has demonstrated that citrus apomixis may be caused by the expression of a gene known as CitRWP (Cg4g018970), which encodes a protein with an RWP-PK domain [16]. Similarly, OsRKD3 can regulate somatic embryogenesis in black rice [18]. According to the results of the phylogenetic tree analysis, four genes (ZaRKD2, ZaRKD8, ZaRKD9, and ZaRKD15) in Z. armatum were most closely related to CitRWP, and three genes (ZaRKD10, ZaRKD13, and ZaRKD14) were most closely related to OsRKD3 (Figure 4).…”

“…Transgenic sweet oranges that lack CitRKD1 function undergo no somatic embryogenesis [17]. In addition, overexpression of OsRKD3 in black rice induces somatic embryogenesis [18].…”

A comprehensive review of in planta stable transformation strategies

“…As such, their expression is critical for de novo shoot organogenesis. Morphogenic regulators promote the production of somatic embryos or embryo-like structures on vegetative or callus explants, an effect that is increased upon overexpression [167][168][169]. Current reports have demonstrated that ectopicly expressed morphogenic regulators can be harnessed to improve the in vitro recovery rates of transgenic calli from hard-to-transform genotypes of at least 12 commercially important monocot species (e.g.…”