Zhou X.; Weng Y.; Su W.; Ye C.; Qu H. and Li Q.Q. 2023. Frontiers in Plant Science 13.
Vivipary is a rare sexual reproduction phenomenon where embryos germinate directly on the maternal plants. However, it is a common genetic event of woody mangroves in the Rhizophoraceae family. The ecological benefits of vivipary in mangroves include the nurturing of seedlings in harsh coastal and saline environments, but the genetic and molecular mechanisms of vivipary remain unclear. Here we investigate the viviparous embryo development and germination processes in mangrove Kandelia obovata by a transcriptomic approach. Many key biological pathways and functional genes were enriched in different tissues and stages, contributing to vivipary. Reduced production of abscisic acid set a non-dormant condition for the embryo to germinate directly. Genes involved in the metabolism of and response to other phytohormones (gibberellic acid, brassinosteroids, cytokinin, and auxin) are expressed precociously in the axis of non-vivipary stages, thus promoting the embryo to grow through the seed coat. Network analysis of these genes identified the central regulatory roles of LEC1 and FUS3, which maintain embryo identity in Arabidopsis. Moreover, photosynthesis related pathways were significantly up-regulated in viviparous embryos, and substance transporter genes were highly expressed in the seed coat, suggesting a partial self-provision and maternal nursing. We conclude that the viviparous phenomenon is a combinatorial result of precocious loss of dormancy and enhanced germination potential during viviparous seed development. These results shed light on the relationship between seed development and germination, where the continual growth of the embryo replaces a biphasic phenomenon until a mature propagule is established.
The reproductive process of viviparous and global gene-expression pattern in K, obovata. (A) The whole viviparous process from ovule to mature hypocotyl. (a) ovule stage (Stage1, S1); (b) enlarged growing seed (S2) and aborted ovules, the insert shows green and linear-shaped embryo; (c) developing seed about to germinate with the embryo enclosed in seed coat and pericarp (S3); (d) germinated seed whose axis protrudes out of the testa but within pericarp (S4); (e) elongating axis reached the edge of the pericarp (S5); (f) axis grows out of pericarp (S6); (g) with ink marked on hypocotyl in the field, 40d later, the upper zone in (h) show expansion while the rest remain the same. ao, aborted ovule; coty, cotyledon; f, funicle; em, embryo; o, ovule; p, pericarp; sc, seed coat. (B) Principal Component Analysis (PCA) of gene expression of 10 samples showing the three replicates of each sample were cluster well. (C) Differential Express Genes (DEGs) numbers in pair-wise comparisons of different tissues and stages from more to less showing tissue heterogeneity are more obvious than stage differences.
