Abstract Detail

Comparative Genomics/Transcriptomics

Peredo, Elena L. [1], Cardon, Zoe G. [2].

Downregulation distinguishes desert from aquatic green algal response to desiccation.

Desiccation tolerance is rare but deeply rooted in the green plant phylogeny. Still relatively frequent in bryophytes, desiccation tolerance in vegetative green tissues was lost during seed plant radiation and secondarily acquired in resurrection seed plants by co-opting metabolic pathways controlling seed development. Similar physiological responses to desiccation among desiccation tolerant (DT) cyanobacteria, green algae, and mosses suggest an ancestral origin of desiccation tolerance in photosynthetic tissues. This is further supported by the discovery of shared molecular responses to desiccation among DT seed plants and terrestrial streptophyte algae. These responses include the increased expression of transcripts coding for Late Embryogenesis Abundant proteins (LEA), components of biosynthetic pathways for oligosaccharide osmolytes, and reactive oxygen species (ROS) protection.Here, we identified these common molecular responses to desiccation in free living, unicellular green algae more distant phylogenetically from embryophytes—in the chlorophyte clade. Our results extend the green plant phylogenetic space in which common molecular pathways supporting desiccation tolerance are known to operate and strongly suggest that molecular circuitry supporting vegetative desiccation tolerance is indeed ancestral in the green plant clade.To better identify the adaptations conferring desiccation tolerance, we investigated the changes in gene expression during desiccation and rehydration in tolerant and intolerant algal taxa, all within the family Scenedesmaceae (Chlorophyte). The tolerant taxa are independently-evolved desert-adapted microalgae isolated from microbiotic soil crusts while the intolerant alga is a closely related aquatic species. The comparison of closely-related desert and aquatic green algae was critical to revealing that in all taxa, independently of their tolerance to desiccation, water loss triggered the expression of the genes that are commonly induced by water loss in diverse DT green plants. We identified increased expression in all algal taxa of genes encoding for LEA proteins, ROS scavengers, and with photoprotective role, such as Early Light Inductible Proteins. However, the feature distinguishing gene expression patterns in desert algae was the extensive downregulation of genes associated with diverse metabolic processes during the desiccation time course. This widespread downshift, consistent with a switch from active growth to energy-saving metabolism, did not occur in the desiccation intolerant aquatic alga. These results show that the desiccation-induced increase in expression of protective genes may be necessary but is not sufficient to confer desiccation tolerance. Rather, the data suggest desiccation tolerance may emerge by combining such protective functions with rewiring of regulatory mechanisms to orchestrate ordered, metabolic slowdown during water stress.

Related Links:
Zoe Cardon
Elena L Peredo

1 - Marine Biological Laboratory, The Ecosystems Center, 7 MBL St, Starr Building, Woods Hole, MA, 02543, United States
2 - Marine Biological Laboratory, 7 MBL st, Woods Hole, Massachusetts, 02543, United States

desiccation tolerance

Presentation Type: Oral Paper
Session: CG1, Functional & Comparative Genetics/Genomics I
Location: Virtual/Virtual
Date: Tuesday, July 28th, 2020
Time: 1:30 PM
Number: CG1005
Abstract ID:451
Candidate for Awards:None

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