What is it about?

Deserts of the U.S. Southwest are extreme habitats for most plants, but, remarkably, microscopic green algae live there that are extraordinarily tolerant of dehydration. These tiny green algae (many just a few microns in size) live embedded in microbiotic soil crusts, which are characteristic of arid areas and are formed by communities of bacteria, lichens, microalgae, fungi, and even small mosses. After completely drying out, the algae can become active and start photosynthesizing again within seconds of receiving a drop of water.

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Why is it important?

How are they so resilient? Understanding the mechanisms that allow the survival of these desert-evolved green microalgae is the question is at the core of our research. These green microalgae are green plants, sharing physiology, cellular structure, and part of their evolutionary history with seed plants. Given the intensified droughts and altered precipitation patterns predicted as the global climate warms, understanding the adaptations that facilitate green plant survival in arid environments is pressing.

Perspectives

We work with two particularly resilient species of green microalgae (Acutodesmus deserticola and Flechtneria rotunda), and we studied up- and down-regulation of gene expression during desiccation. We also analyzed gene expression in a close aquatic relative (Enallax costatus) as it dried out and ultimately died. Surprisingly, all three algae – desiccation tolerant or not – upregulated the expression of groups of genes known to protect even seed plants during drought. But the desiccation-tolerant algae also ramped down expression of genes coding for many other basic cellular processes, seemingly putting the brakes on their metabolism. The aquatic relative did not. Our research suggest that this new perspective on desiccation tolerance warrants investigation in green plants more broadly. Upregulation of gene expression coding for protective proteins may be necessary but not sufficient; downregulation of diverse metabolic genes may also be key to survival.

Elena Peredo
Marine Biological Laboratory

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This page is a summary of: Shared up-regulation and contrasting down-regulation of gene expression distinguish desiccation-tolerant from intolerant green algae, Proceedings of the National Academy of Sciences, July 2020, Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.1906904117.
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