Comparative transcriptomics of seed nourishing tissues: uncovering conserved and divergent pathways in seed plants

Abstract

SummaryThe evolutionary and ecological success of Spermatophytes is intrinsically linked to the seed habit, which provides a protective environment for the pre-development of the new generation. This environment includes an ephemeral nourishing tissue that supports embryo growth. In gymnosperms this tissue originates from the asexual proliferation of the maternal megagametophyte, while in angiosperms it is a product of fertilization, and is called the endosperm. The emergence of these nourishing tissues is of profound evolutionary value, and they are also food staples for most of the world’s population. Here, using orthogroup inference, we provide a comparative transcriptomic analysis of seed nourishing tissues from representative species of all main angiosperm clades, including those of early diverging basal angiosperms, and of two gymnosperm representatives. Our results show that, although the structure and composition of seed nourishing tissues has seen significant divergence along evolution, there are signatures that are conserved throughout the phylogeny. Conversely, we identified processes that are exclusive to each clade, and thus illustrate their functional divergence. With this, we aimed to provide a foundation for future studies on the evolutionary history of seed nourishing structures, as well as a resource for gene discovery in new functional studies.Significance StatementWithin seeds a specialized structure is responsible for nourishing the embryo, and is thus analogous to the mammalian placenta. Moreover, these nourishing tissues are also important sources of staple foods and feed. Here, we provide novel gene expression datasets of nourishing tissues of early diverging angiosperms, and use this information for a meta-analysis to identify pathways conserved, or divergent, throughout evolution. Thus, we aim to provide a resource for gene discovery for seed biology studies.

The maternal embrace: the protection of plant embryos

“…It has also been shown that brassinosteroids are involved in signalling between the maternal seed coat and the endosperm ( Lima et al , 2023 , Preprint). These hormonal exchanges seem very conserved in most angiosperms ( Florez-Rueda et al , 2023 , Preprint). Likewise, the central cell-derived ESF1 peptides contribute to proper embryo development ( Costa et al , 2014 ), and even maternal morphogenetic signals are suggested to be involved in embryo patterning in Arabidopsis ( Ray et al , 1996 ).…”