Galactomannan biosynthesis in coffee seeds

In few important plant families and genera, including Arecaceae, Fabaceae and the genus Coffea, the main seed storage polysaccharide is not starch but cell wall galactomannans. Such seeds are albuminous with a persistent copious living endosperm that accumulates galactomannans. However, our understanding of the regulation of endosperm maturation, cell wall formation and galactomannan biosynthesis in albuminous seeds remains very limited. To gain insights into these processes, a large RNA-seq dataset was produced (14 coffee species × 5 endosperm developmental stages) and scrutinized through gene coexpression network analysis. The orchestration of galactomannan and oil accumulation during endosperm maturation appeared to be exerted by the transcription factors FUSCA3, WRINKLED1, SHINE2 and DREB2D, which was the only coexpression partner of galactomannan biosynthetic genes. Numerous key genes of galactomannan biosynthesis were significantly upregulated in coffee somatic embryos overexpressing DREB2D, which showed an increased production of UDP-galactose and diversion towards raffinose family oligosaccharides. The Illumina-based RNAseq data included in this ENA project correspond to : * 60 seed endosperm samples from 14 coffee species collected at 5 different maturation stages (ST3 to ST7); the other 9 samples used in the study have already been deposited; * 10 somatic embryo samples (at cotyledon stage) comprising 6 independent transgenic lines (overexpressing the DREB2D gene and coded D1 to D6) and 4 control lines (PMDC, coded C1 to C4).