| How plants came to have seeds during evolution remains an intriguing question in plant evolutionary studies. Seed development comprises two major phases:the early morphogenesis phase and the late maturation phase. During the maturation phase, the seed accumulates various storage compounds and acquires desiccation tolerance, and eventually enters dormancy. These processes were also observed in spore development in plants that lacked a dormant embryonic phase of development. It has thus been proposed that the acquisition of the seed habit in the seed plant lineage probably resulted from a heterochronic switch of the storage compound accumulation and dormancy programs from a pre-embryonic (spore) phase of the plant life cycle to a postembryonic phase.In this study, we conducted a deep sequencing-based transcriptome analysis of spore development in Selaginelia moellendorffii. A total of5046genes were identified as differentially displayed. By comparing with the expression patterns of best-matched homologous genes in Arabidopsis thaliana, we found251genes that exhibited similar patterns of differential expression during seed maturation. The up-regulated genes were mostly related to storage protiens synthesis, lipid synthesis, cellular response to osmotic stress, and secondary metabolite biosynthesis, while most of the down-regulated genes were involved in photosynthesis, cell cycle control and mitosis. The results of this study suggest that dormancy in angiosperm seeds and fern spores requires the synthesis and accumulation of similar storage compounds, even though the two structures represent very different phases of the plant life cycle. This initial comparative analysis also suggests that the gene regulatory networks controlling seed development and maturation have evolved through the co-option of pre-existing regulatory module, providing new insights into the evolutionary developmental mechanism of the seed habitat. |
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