Transcriptional insights into molecular events occurring during tuber maturation of tigernut (Cyperus esculentus L.)

Tigernut (Cyperus esculentus L. var. sativus Boeck., Cyperaceae), an emerging oilcrop, is unique for producing desiccation-tolerant tubers. However, thus far, the underlying mechanisms are largely unknown. To gain insights into molecular events occurring during tuber maturation, deep sequencing was used to investigate gene expression profiles of two representative tuber stages of Reyan3, i.e., immature and mature, whose tubers were characterized by light and dark brown in color and with the moisture content of 74.80% and 48.30%, respectively. A total of 16,499 genes were shown to be expressed, accounting for approximately 69.87% of 23,613 protein-coding genes predicted in the genome. Notably, functional annotation revealed a seed-like transcriptome. Furthermore, a number of 519 differentially expressed genes (DEGs) were identified, including 191 upregulated and 328 downregulated in mature tubers relative to immature ones, which were supported by qRT-PCR analysis. Functional analysis showed that these DEGs are especially enriched in certain Gene Ontology terms such as Cellular process, Metabolic process, Response to stimulus, Biological regulation, Regulation of biological process, Cellular anatomical entity, Binding, and Catalytic activity. Moreover, the upregulated DEGs include eight LEA (late embryogenesis-abundant) genes and two sHSP (small heat shock protein) genes, and are specifically enriched in Seed maturation, Iron ion binding, Monooxygenase activity, Oxidoreductase activity, and Response to heat, supporting an orthodox seed-like transcription during tuber maturation, though the regulatory mechanisms appear to be different. These findings provide a first global view of molecular events occurring during tuber maturation in tigernut, which shed light on the mechanisms of desiccation tolerance acquisition in vegetative tissues.