Research Center for Biotechnology, Universitas Gadjah Mada Jl. Teknika Utara, Depok, Sleman, Yogyakarta, Indonesia, 55281.
Department of Tropical Biology, Faculty of Biology, Universitas Gadjah Mada Jl. Teknika Selatan, Sekip Utara, Yogyakarta, Indonesia, 55281.
BMC Plant Biol. 2023 Apr 19;23(1):202. doi: 10.1186/s12870-023-04220-z.
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.
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.
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.
植物具有从配子和体细胞形成胚胎的独特能力，后者过程被称为体细胞胚胎发生。体细胞胚胎发生（SE）可以通过将植物组织暴露于外源生长调节剂或通过胚胎发生转录因子的异位激活来诱导。最近的研究表明，一组离散的富含 RWP-RK 结构域的蛋白（RKD）转录因子作为陆地植物生殖细胞分化和胚胎发育的关键调节剂。生殖 RKD 的异位过表达与细胞增殖增加和体细胞胚样结构的形成有关，这些结构绕过了对外源生长调节剂的需求。然而，RKD 转录因子诱导体细胞胚胎发生的确切分子机制尚不清楚。
通过计算机分析，我们鉴定了一个水稻 RWP-RK 转录因子，命名为 Oryza sativa RKD3（OsRKD3），它与拟南芥 AtRKD4 和 Marchantia polymorpha RKD（MpRKD）蛋白密切相关。我们的研究表明，在通常对体细胞胚胎发生具有抗性的印度尼西亚黑米地方品种（Cempo Ireng）中，异位过表达 OsRKD3，该蛋白在生殖组织中优先表达，可以触发体细胞胚胎的形成。通过分析诱导组织的转录组，我们鉴定出 5991 个基因对 OsRKD3 诱导表现出差异表达。这些基因中，有 50%上调，另一半下调。值得注意的是，约 37.5%的上调基因在其启动子区域含有一个序列基序，该基序也在拟南芥的 RKD 靶标中观察到。此外，OsRKD3 被证明介导了一个离散基因网络的转录激活，该网络包括几个转录因子，如 APETALA 2 样（AP2-like）/ETHYLENE RESPONSE FACTOR（ERF）、MYB 和 CONSTANS-like（COL），以及与激素信号转导、应激反应和胚胎后途径相关的染色质重塑因子。
我们的数据表明，OsRKD3 调节广泛的基因网络，其激活与体细胞胚胎程序的启动有关，这有利于黑米的遗传转化。这些发现为提高黑稻的作物生产力和推进农业实践提供了巨大的潜力。
