FUS3 Activates TAG Accumulation

Triacylglycerol (TAG) is the main storage lipid in plant seeds and the major form of plant oil used for food and, increasingly, for industrial and biofuel applications. Several transcription factors, including FUSCA3 (At3g26790, FUS3), are associated with regulation of embryo 3maturation and oil biosynthesis in seeds. However, the ability of FUS3 to increase TAG biosynthesis in other tissues has not been quantitatively examined. Here, we evaluated the ability of FUS3 to activate TAG accumulation in non-seed tissues. Overexpression of FUS3 driven by an estradiol-inducible promoter increased oil contents in Arabidopsis seedlings up to 6% of dry weight; more than 50 fold over controls. Eicosenoic acid, a characteristic fatty acid of Arabidopsis seed oil, accumulated to over 20% of fatty acids in cotyledons and leaves. These large increases depended on added sucrose, although without sucrose TAG increased 3-4 fold. Inducing the expression of FUS3 in tobacco BY2 cells also increased TAG accumulation, and co-expression of FUS3 and diacylglycerol acyltransferase 1 (DGAT1) further increased TAG levels to 4% of dry weight. BY2 cell growth was not altered by FUS3 expression, although Arabidopsis seedling development was impaired, consistent with the ability of FUS3 to induce embryo characteristics in non-seed tissues. Microarrays of Arabidopsis seedlings revealed that FUS3 overexpression increased expression of a higher proportion of genes involved in TAG biosynthesis than genes involved in fatty acid biosynthesis or other lipid pathways. Together these results provide additional insights into FUS3 functions in TAG metabolism and suggest complementary strategies for engineering vegetative oil accumulation. To investigate gene expression patterns in vegetative tissues expressing FUS3 and the interactions between FUS3, sucrose and oil accumulation, we characterized the transcriptome of Arabidopsis seedlings that accumulated oil using Arabidopsis ATH1 microarrays. We grew ESTpro:FUS3-strong and WT plants under FUS3-inducing conditions on medium with or without sucrose, extracted total RNA from 8-day-old seedlings from triplicate biological samples, and performed transcriptome profiling using the Affymetrix GeneChip ATH1. A two-way ANOVA test was performed to evaluate differential expression across groups, and their interactions were defined based on two factors, namely, FUS3 induction and sucrose treatment.