GENOMIC APPLICATIONS TO PLANT BIOLOGY

The study of the total nuclear DNA content of an organism, i.e., the genome, is a relatively new field and has evolved as sequencing technology and its output has changed. A shift from model species to ecological and crop species occurred as sequencing costs decreased and the technology became more broadly accessible, enabling new discoveries in genome biology as increasingly diverse species and populations were profiled. Here, a genome assembly and several transcriptional studies in multiple non-model plant species provided new knowledge of molecular pathways and gene content. Over 157 Mb of the genome of the medicinal plant species Calotropis gigantea (L.) W.T.Aiton was sequenced, de novo assembled and annotated using Next Generation Sequencing technologies. The resulting assembly represents 92% of the genic space and provides a resource for discovery of the enzymes involved in biosynthesis of the anticancer metabolite, cardenolide. An updated gene expression atlas for 79 developmental maize (Zea mays L., 1753) tissues and five abiotic/biotic stress treatments was developed, revealing 4,154 organ-specific and 7,704 stress-induced differentially expressed (DE) genes. Presence-absence variants (PAVs) were enriched for organ-specific and stress-induced DE genes, tended to be lowly expressed, and had few co-expression network connections, suggesting that PAVs function in environmental adaptation and are on an evolutionary path to pseudogenization. The Maize Genomics Resource (http://maize.plantbiology.msu.edu/) was developed to view and data-mine these resources. Through profiling global gene expression over time in potato (Solanum tuberosum L.) leaf and tuber tissue, the first circadian rhythmic gene expression profiles of the below-ground heterotrophic tuber tissue were generated. The tuber displayed a longer circadian period, a delayed phase, and a lower amplitude compared to leaf tissue. Over 500 genes were differentially phased between the leaf and tuber, and many carbohydrate metabolism enzymes are under both diurnal and circadian regulation, reflecting the importance of the circadian clock for tuber bulking. Most core circadian clock genes do not display circadian rhythmic gene expression in the leaf or tuber, yet robust transcriptional and gene expression circadian rhythms are present.