Co-expression of hydrolase genes improves seed germination of Sinopodophyllum hexandrum

Sinopodophyllum hexandrum is a perennial rhizomatous herb and its rhizome produces anti-cancer compound podophyllotoxin (PPT). As a result of overexploitation of wild resources and lack of large-scale cultivation, it is currently an endangered species. An effective and conventional propagation method is by seed, but seed germination is erratic attributed to the barriers from seed coat and thick-walled endosperm. While several proteins and genes that are involved in cell wall loosening and endosperm weakening have been identified, the mechanism responsible for regulating germination has not been systematically mapped. Here, transcriptomics profiles of S. hexandrum during seed germination were performed, genes expression was validated as well as metabolites and hormones were measured. Over one thousand genes were observed to be differentially co-expressed at the five germination stages. Functional annotation classified 67 genes associated with cell wall loosening and endosperm weakening (25), primary metabolism and energy (16), hormone biosynthesis and bio-signaling (15), radicle growth (5), and transcription factor (6). The expression levels of genes involved in hydrolases (i.e. XTHs, GLCs, MANs, EXPAs, AGALs, PECSs and PGs), metabolites (i.e. starch, oligosaccharides, proteins, lipids and fatty acids) and hormones (i.e. GA3, ABA and IAA) were almost consistent with changes of seed water uptake, contents of metabolites and hormones, and cell wall modifications. This combinational analysis of transcriptomics with targeted metabolites and hormones provides new insights into seed germination of S. hexandrum.