Transcription factor bZIP52 modulates Arabidopsis seed oil biosynthesis through interaction with WRINKLED1.

Transcriptional regulation mediated by combinatorial interaction of transcription factors (TFs) is a key molecular mechanism modulating plant development and metabolism. Basic leucine zipper (bZIP) TFs play important roles in various plant developmental and physiological processes. However, their involvement in fatty acid biosynthesis is largely unknown. Arabidopsis (Arabidopsis thaliana) WRINKLED1 (WRI1) is a pivotal TF in regulation of plant oil biosynthesis and interacts with other positive and negative regulators. In this study, we identified two bZIP TFs, bZIP21 and bZIP52, as interacting partners of AtWRI1 by yeast-two-hybrid (Y2H)-based screening of an Arabidopsis TF library. We found that coexpression of bZIP52, but not bZIP21, with AtWRI1 reduced AtWRI1-mediated oil biosynthesis in Nicotiana benthamiana leaves. The AtWRI1-bZIP52 interaction was further verified by Y2H, in vitro pull-down, and bimolecular fluorescence complementation assays. Transgenic Arabidopsis plants overexpressing bZIP52 showed reduced seed oil accumulation, while the CRISPR/Cas9-edited bzip52 knockout mutant exhibited increased seed oil accumulation. Further analysis revealed that bZIP52 represses the transcriptional activity of AtWRI1 on the fatty acid biosynthetic gene promoters. Together, our findings suggest that bZIP52 represses fatty acid biosynthesis genes through interaction with AtWRI1, resulting in a reduction of oil production. Our work reports a previously uncharacterized regulatory mechanism that enables fine-tuning of seed oil biosynthesis.

Molecular basis of the key regulator WRINKLED1 in plant oil biosynthesis.

Vegetable oils are not only major components of human diet but also vital for industrial applications. WRINKLED1 (WRI1) is a pivotal transcription factor governing plant oil biosynthesis, but the underlying DNA-binding mechanism remains incompletely understood. Here, we resolved the structure of Arabidopsis WRI1 (AtWRI1) with its cognate double-stranded DNA (dsDNA), revealing two antiparallel ß sheets in the tandem AP2 domains that intercalate into the adjacent major grooves of dsDNA to determine the sequence recognition specificity. We showed that AtWRI1 represented a previously unidentified structural fold and DNA-binding mode. Mutations of the key residues interacting with DNA element affected its binding affinity and oil biosynthesis when these variants were transiently expressed in tobacco leaves. Seed oil content was enhanced in stable transgenic wri1-1 expressing an AtWRI1 variant (W74R). Together, our findings offer a structural basis explaining WRI1 recognition and binding of DNA and suggest an alternative strategy to increase oil yield in crops through WRI1 bioengineering.

The function of the WRI1-TCP4 regulatory module in lipid biosynthesis.

The plant-specific TCP transcription factors play pivotal roles in various processes of plant growth and development. However, little is known regarding the functions of TCPs in plant oil biosynthesis. Our recent work showed that TCP4 mediates oil production via interaction with WRINKLED1 (WRI1), an essential transcription factor governing plant fatty acid biosynthesis. Arabidopsis WRI1 (AtWRI1) physically interacts with multiple TCPs, including TCP4, TCP10, and TCP24. Transient co-expression of AtWRI1 with TCP4, but not TCP10 or TCP24, represses oil accumulation in Nicotiana benthamiana leaves. Increased TCP4 in transgenic plants overexpressing a miR319-resistant TCP4 (rTCP4) decreased the expression of AtWRI1 target genes. The tcp4 knockout mutant, the jaw-D mutant with significant reduction of TCP4 expression, and a tcp2 tcp4 tcp10 triple mutant, display increased seed oil contents compared to the wild-type Arabidopsis. The APETALA2 (AP2) transcription factor WRI1 is characterized by regulating fatty acid biosynthesis through cross-family interactions with multiple transcriptional, post-transcriptional, and post-translational regulators. The interacting regulator modules control the range of AtWRI1 transcriptional activity, allowing spatiotemporal modulation of lipid production. Interaction of TCP4 with AtWRI1, which results in a reduction of AtWRI1 activity, represents a newly discovered mechanism that enables the fine-tuning of plant oil biosynthesis.