Non-Zygotic Embryogenesis in Hardwood Species

First author: Elena Corredoira; Affiliations: Instituto de Investigaciones Agrobiológicas de Galicia (加利西亚农业生物研究所): Santiago de Compostela, Spain

Corresponding author: Elena Corredoira

Hardwood species are valuable biological resources that have an important role in the economy and ecology of ecosystems worldwide. Non-zygotic or somatic embryogenesis (SE) is a powerful tool in plant biotechnology as it is a form of clonal propagation, amenable to cryopreservation of valuable germplasm and genetic transformation including gene editing. The SE process involves five steps and includes somatic embryo induction, proliferation, maturation, plantlet conversion, and subsequent plant acclimatization. This review aims to provide a general overview of these steps in different SE systems developed for hardwood species. Factors that influence the induction stage such as the age of the donor plant, genotype and culture media are discussed. The role of different explant types, i.e. zygotic embryos and non-zygotic tissues, such as roots, flower tissues, nodes, internodes, leaves or shoot apices, in SE induction are especially emphasized. Histological studies of the origin of somatic embryos and the sequence of events leading to their development from initial explants are assessed. Maintenance of embryogenic capacity carried out by subculture of embryogenic inocula on semisolid or liquid media through cell suspension cultures or by temporary immersion systems is described. At present, the main concerns associated with the application of SE for large-scale propagation of elite hardwoods are related to the embryo maturation, germination, and plantlet conversion steps, and these are highlighted in this review. Finally, molecular aspects associated with somatic embryo induction and development are also described. Attempts to overcome the hurdles identified in the embryogenic process, and future lines of research are proposed.

阔叶树种是珍贵的生物资源，对于全球的经济和生态系统都具有非常重要的作用。非合子或体细胞胚胎发生是植物生物技术中一种无性繁殖的方法，能够用于珍稀种质资源的冷冻保存和基因编辑在内的遗传转化。体胚过程一共包括五个阶段：分别是体细胞胚胎诱导、增殖、成熟、幼苗转换以及随后的环境适应。本文综述了针对不同阔叶树种开发的体胚系统。作者讨论了影响体胚诱导阶段的因素，包括供体植株的树龄、基因型和培养基。作者还着重讨论了用于体细胞胚胎发生的不同外植体类型，比如合子胚胎和根、花、节间、叶片或茎尖等非合子组织。作者评估了体细胞胚胎来源的组织学研究以及促进体细胞胚胎从外植体起始到最终形成的一系列事件。作者还讨论了将具有胚性的细胞接种到半固体或液体培养基中，通过细胞悬浮培养或临时浸入系统来保持材料的胚性。目前，体细胞胚胎发生用于大规模繁育优质阔叶树种的实践应用关键步骤在于胚胎的成熟、萌发以及幼苗转换阶段，作者在本文中也讨论了这部分的内容。最后，作者还讨论了与体细胞胚胎诱导和发育相关的分子机制。为了能够克服胚胎发育过程中某些已经确定了的障碍，作者提出了未来相关研究的一些方向。

doi: https://doi.org/10.1080/07352689.2018.1551122

Journal: Critical Reviews in Plant Sciences 

Published online: February 14, 2019