Meeting Abstract
Desiccation tolerance in the vegetative state (DT) is an essential adaptive trait for colonization of land. DT has evolved independently in multiple lineages of terrestrial green algae, including in the algal ancestor of all seed plants. Scenedesmaceae is a particularly powerful group of microalgae for the study of DT because the group includes multiple, independently-evolved desert-dwelling species and very closely-related aquatic taxa. Desiccated desert algae recover photosynthetic activity immediately when rehydrated, whereas their aquatic relatives display very limited to no recovery upon rehydration. Desert-evolved taxa also minimize accumulation of reactive oxygen species during water loss. Gene expression patterns during desiccation and rehydration reveal that during desiccation, desiccation-tolerant taxa first downregulate photosynthesis and energetic metabolism then notably increase expression of genes and transcription factors traditionally associated with stress in the broad green plant clade, including Late Embryogenesis Abundant proteins, small Heat Shock Proteins and oxidoreductases. The controlled response in desert-evolved taxa contrasts with an overall upregulation of gene expression observed in the aquatic taxa, consistent with a state of cellular emergency during desiccation. These data suggest that desiccation tolerance may rely on both the coordinated expression of multiple (potentially ancient) genes and pathways protecting cellular structures from damage, and the induction of regulatory networks that control an ordered cellular shutdown under unfavorable conditions. The shift towards a more quiescent metabolism during stress might be as important for DT as the induced expression of well-recognized, stress-related proteins.
