Prospects for analyzing ancient RNA in preserved materials

An ever increasing wealth of ancient biological material is providing opportunities to study biomolecules. Animal, plant, and microbial samples dating back hundreds, thousands, and even millions of years have been preserved in a dry state under climatic conditions ranging from the arctic to hot deserts. Various small molecules, often crystalized or polymerized, have improved preservation. Modern methods such as polymerase chain reaction (PCR), mass spectrometry, and shotgun sequencing have detected and characterized ancient biomolecules. Modern sequencing has the capacity not only to assemble the whole genome of the target host but also those of the host's parasites, mutualists, and commensals. The study of ancient RNA has barely begun. Several studies show that RNA has been preserved for decades to hundreds of years and the germination of ancient seeds implies that messenger RNA can be preserved for thousands of years. This review briefly examines the types of ancient materials available and assesses their suitability for the study of ancient RNA. Sequencing RNA from this material has the potential not only to illuminate the target host's transcriptome and small RNAs but also to characterize the host's RNA parasites: viruses and viroids.