<i>WRINKLED1</i>, A Ubiquitous Regulator in Oil Accumulating Tissues from <i>Arabidopsis</i> Embryos to Oil Palm Mesocarp

<div><p>WRINKLED1 (<i>At</i>WRI1) is a key transcription factor in the regulation of plant oil synthesis in seed and non-seed tissues. The structural features of WRI1 important for its function are not well understood. Comparison of WRI1 orthologs across many diverse plant species revealed a conserved 9 bp exon encoding the amino acids “VYL”. Site-directed mutagenesis of amino acids within the ‘VYL’ exon of <i>At</i>WRI1 failed to restore the full oil content of <i>wri1-1</i> seeds, providing direct evidence for an essential role of this small exon in <i>At</i>WRI1 function. <i>Arabidopsis</i> WRI1 is predicted to have three alternative splice forms. To understand expression of these splice forms we performed RNASeq of <i>Arabidopsis</i> developing seeds and queried other EST and RNASeq databases from several tissues and plant species. In all cases, only one splice form was detected and VYL was observed in transcripts of all WRI1 orthologs investigated. We also characterized a phylogenetically distant WRI1 ortholog (<i>Eg</i>WRI1) as an example of a non-seed isoform that is highly expressed in the mesocarp tissue of oil palm. The C-terminal region of <i>Eg</i>WRI1 is over 90 amino acids shorter than <i>At</i>WRI1 and has surprisingly low sequence conservation. Nevertheless, the <i>Eg</i>WRI1 protein can restore multiple phenotypes of the <i>Arabidopsis</i><i> wri1-1</i> loss-of-function mutant, including reduced seed oil, the “wrinkled” seed coat, reduced seed germination, and impaired seedling establishment. Taken together, this study provides an example of combining phylogenetic analysis with mutagenesis, deep-sequencing technology and computational analysis to examine key elements of the structure and function of the WRI1 plant transcription factor.</p>