Abstract
Understanding the molecular basis of morphological shifts is a fundamental question of evolutionary biology. New morphologies may arise through the birth/death of genes (gene gain/loss) or by reutilizing existing gene sets. Yet, the relative contribution of these two processes to radical morphological shifts is still poorly understood. Here, we use the model system of two mosses, Funaria hygrometrica and Physcomitrium (Physcomitrella) patens, to investigate the molecular mechanisms underlying contrasting sporophyte architectures. We used comparative analysis of time-series expression data for four stages of sporophyte development in both species to address this question in detail. We found that large-scale differences in sporophytic architecture are mainly governed by orthologous (i.e., shared) genes frequently experiencing temporal gene expression shifts between the two species. While the absolute number of species-specific genes expressed during sporophyte development is somewhat smaller, we observed a significant increase of their proportion in preferentially sporophyte expressed genes, suggesting a fundamental role in the sporophyte phase. However, further functional studies are necessary to determine their contribution to diverging sporophyte morphologies. Our results add to the growing set of studies suggesting that radical changes in morphology may rely on the heterochronic expression of conserved regulators.
Highlights
The genome is constantly reshaped by diverse types of mutations providing raw material for evolution to work with
To identify genes potentially underlying the difference in sporophyte development between F. hygrometrica and P. patens, we measured gene expression across four distinct stages of sporophyte development and several stages of gametophyte development in both species using RNA-sequencing (Figure 2)
Morphological novelties may be associated with gene birth/death or can alternatively be achieved by existing genes acquiring a new function (Davidson, 2010; Pires and Dolan, 2012; Chen et al, 2013; Schlötterer, 2015; Li et al, 2016; Das Gupta and Tsiantis, 2018; Bowman et al, 2019; Zhang et al, 2019)
Summary
The genome is constantly reshaped by diverse types of mutations providing raw material for evolution to work with. Various molecular mechanisms may underlie the origin of morphological novelties including (i) the rise of novel genes (de novo evolution and introgression of genes). The evolution of many key phenotypic characters has taken another path by co-opting existing genes or complete regulatory networks to create new morphological features (Rast-Somssich et al, 2015; Rebeiz and Tsiantis, 2017). Revealing the molecular processes underlying phenotypic changes in a diverse set of model systems may help to discover key commonalities of the evolutionary process and assess how gene gain/loss and co-option of existing genes for new functions may contribute to morphological evolution
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