Transcriptomic and lipidomic analysis of the differential pathway contribution for the incorporation of erucic acid to triacylglycerol during pennycress seed maturation
Thlaspi arvense (Pennycress) is an emerging feedstock for biofuel production because of its high seed oil content enriched in erucic acid. A transcriptomic and a lipidomic study were performed to analyze the dynamics of gene expression, glycerolipid content and acyl-group distribution during seed maturation. Genes involved in fatty acid biosynthesis were expressed at the early stages of seed maturation. Genes encoding enzymes of the Kennedy pathway like TaDGAT1, TaLPAT or TaGPAT increased their expression with maturation, coinciding with the increase in TAG species containing 22:1. Positional analysis showed that the most abundant TAG species contained 18:2 at sn-2 position in all maturation stages, suggesting no specificity of the TaLPAT for VLCFAs. TaDGAT2 mRNA was more abundant at the initial maturation stages, coincident with the rapid incorporation of 22:1 to TAG, suggesting a coordination between DGAT enzymes for TAG biosynthesis. Genes encoding TaPDAT1, TaLPCAT or TaPDCT, involved in acyl-editing or PC-derived DAG/TAG biosynthesis showed also higher expression at the early maturation stages, coinciding with a higher proportion of TAG species containing C18 fatty acids. These results suggested a higher contribution of these two pathways at the early stages of seed maturation. LC-MS analysis of the content and acyl-group distribution of DAG and PC pools was compatible with the acyl content in TAG at the different maturation stages. Our data point to a model in which a strong temporal coordination between pathways and isoforms in each pathway, both at the expression and acyl-group incorporation, contributes to high erucic TAG accumulation in Pennycress. Overall design: Seeds from five developmental stages corresponding to GREEN (G, 12 days after flowering, DAF), GREENYELLOW (GY, 19 DAF), YELLOWGREEN (YG, 26 DAF), YELLOW (Y, 33DAF) and MATURE (M, 45 DAF), were chosen for analysis. Seeds separated from the pods, corresponding to these different maturation stages, harvested, frozen in liquid nitrogen, and stored at -80 ºC for further analysis. RNA-Seq libraries were prepared and sequenced on an Illumina NovaSeq6000 at Novogene Ltd (www.novogene.uk). Ten libraries, corresponding to two biological replicates of the five different seed developmental stages Comparative gene expression analysis of the RNA-Seq data for the GREEN, GREENYELLOW, YELLOWGREEN, YELLOW and MATURE seed maturation stages was performed.