Environmental gradients reveal stress hubs predating plant terrestrialization

Abstract

Plant terrestrialization brought forth the land plants (embryophytes). Embryophytes account for most of the biomass on land and evolved from streptophyte algae in a singular event. Recent advances have unraveled the first full genomes of the closest algal relatives of land plants; among the first such species was Mesotaenium endlicherianum. Here, we used fine-combed RNAseq in tandem with photophysiological assessment on Mesotaenium exposed to a continuous range of temperature and light cues. Our data establish a grid of 42 different conditions, resulting in 128 transcriptomes and ~1.5 Tbp (~9.9 billion reads) of data to study combinatory effects of stress response using clustering along gradients. We describe major hubs in genetic networks underpinning stress response and acclimation in the molecular physiology of Mesotaenium. Our data suggest that lipid droplet formation, plastid and cell wall-derived signals denominate molecular programs since more than 600 million years of streptophyte evolution - before plants made their first steps on land.

3D‐reconstructions of zygospores in Zygnema vaginatum (Charophyta) reveal details of cell wall formation, suggesting adaptations to extreme habitats

“…During conjugation, increased levels of oleosin transcripts were found in Spirogyra grevilleana, suggesting their role in zygospore wall formation (Huang et al, 2013). Overall, data indicate that LDs of streptophyte algae are more similar to those found in land plants than in other Charophyta and that oleosins could already be major LD proteins in Zygnematophyceae (Dadras et al, 2022;de Vries & Ischebeck, 2020).…”

Divergent responses in desiccation experiments in two ecophysiologically different Zygnematophyceae

“…There is a concept that calcium signaling emerged early during streptophyte evolution (Edel et al 2017; Edel and Kudla 2015). And the more stress experiments are conducted on Zygnematophyceae, the more frequently expression patterns in genes homologous to components of calcium‐mediated signaling cascades (e.g., CALCIUM‐DEPENDENT PROTEIN KINASE ) are found (Rippin et al 2017; de Vries et al 2020; Dadras et al 2023a). Indeed, recently, some of us described that M. endlicherianum shares the differential regulation of calcium signaling‐related genes upon light and temperature cues with various streptophyte algae challenged by a range of abiotic stressors (Dadras et al 2023a).…”

The impact of salt stress on the physiology and the transcriptome of the model streptophyte green alga Chara braunii

“…These genes were omitted from the further analysis. Exposition of the streptophyte alga Mesotaenium endlicherianum to stress conditions, particularly high temperature, has also had a strong effect on transposable element mobilization (Dadras et al, 2023).…”