Transcriptomic Profiling Of Differential Responses To Drought In Two Freshwater Mussel Species, The Giant Floater Pyganodon Grandis And The Pondhorn Uniomerus Tetralasmus

The southeastern US has experienced recurrent drought during recent decades.Increasing demand for water, as precipitation decreases, exacerbates stress on theaquatic biota of the Southeast: a global hotspot for freshwater mussel, crayfish, andfish diversity. Freshwater unionid mussels are ideal candidates to study linkagesbetween ecophysiological and behavioral responses to drought. Previous work onco-occurring mussel species suggests a coupling of physiology and behavior along agradient ranging from intolerant species such as Pyganodon grandis (giant floater) thattrack receding waters and rarely burrow in the substrates to tolerant species such asUniomerus tetralasmus (pondhorn) thatrarely track receding waters, but readily burrowinto the drying sediments. We utilized a next-generation sequencing-based RNA-seqapproach to examine heat/desiccation-induced transcriptomic profiles of these twospecies in order to identify linkages between patterns of gene expression, physiologyand behavior. Sequencing produced over425million100bp reads. Using the de novoassembly package Trinity, we assembled the short reads into321,250contigs fromgiant floater (average length835bp) and385,735contigs from pondhorn (averagelength929bp). BLAST-based annotation and gene expression analysis revealed2,832differentially expressed genes in giant floater and2,758differentially expressed genesin pondhorn. Trancriptomic responses included changes in molecular chaperones,oxidative stress profiles, cell cycling, energy metabolism, immunity, and cytoskeletalrearrangements. Comparative analyses between species indicated significantly higherinduction of molecular chaperones and cytoskeletal elements in the intolerant P.grandis as well as important differences in genes regulating apoptosis and immunity.