<i>De novo</i> sequencing allows genome-wide identification of genes involved in galactomannan synthesis in locust bean (<i>Ceratonia siliqua</i>)

Locust bean (Ceratonia siliqua) accumulates the galactomannan (GM) locust bean gum (LBG) in its seeds. LBG is a major industrial raw material used as a food thickener and gelling agent, whose unique properties mean that it cannot be readily replaced by other GMs. Whereas much is known about GM accumulation and the genes associated with GM biosynthesis in legumes, the genes involved in GM biosynthesis in C. siliqua are largely unknown. Here, we present a genome-wide list of genes predicted to be associated with the GM biosynthesis pathway in C. siliqua. We confirmed high GM accumulation in endosperm using a newly established GM quantification method involving LC-MS/MS. Through de novo draft genome assembly, we comprehensively identified genes predicted to be related to the GM biosynthesis pathway in C. siliqua by identifying orthologous groups. In particular, we identified all genes predicted to encode mannan synthase (ManS) and galactomannan galactosyltransferase (GMGT), enzymes functioning in the final step of GM biosynthesis, from the C. siliqua draft genome. ManS and the GMGT paralogs were predominantly expressed in endosperm. The genome and transcriptome produced in this study should facilitate research examining why C. siliqua produces LBG, unlike other legumes.