Splice Variants of the Castor WRI1 Gene Upregulate Fatty Acid and Oil Biosynthesis When Expressed in Tobacco Leaves

Abstract

The plant-specific WRINKLED1 (WRI1) is a member of the AP2/EREBP class of transcription factors that positively regulate oil biosynthesis in plant tissues. Limited information is available for the role of WRI1 in oil biosynthesis in castor bean (<i>Ricinus connunis</i> L.), an important industrial oil crop. Here, we report the identification of two alternatively spliced transcripts of <i>RcWRI1</i>, designated as <i>RcWRI1-A</i> and <i>RcWRI1-B</i>. The open reading frames of <i>RcWRI1-A</i> (1341 bp) and <i>RcWRI1-B</i> (1332 bp) differ by a stretch of 9 bp, such that the predicted RcWRI1-B lacks the three amino acid residues "VYL" that are present in RcWRI1-A. The <i>RcWRI1-A</i> transcript is present in flowers, leaves, pericarps and developing seeds, while the <i>RcWRI1-B</i> mRNA is only detectable in developing seeds. When the two isoforms were individually introduced into an <i>Arabidopsis</i><i>wri1-1</i> loss-of-function mutant, total fatty acid content was almost restored to the wild-type level, and the percentage of the wrinkled seeds was largely reduced in the transgenic lines relative to the <i>wri1-1</i> mutant line. Transient expression of each <i>RcWRI1</i> splice isoform in <i>N. benthamiana</i> leaves upregulated the expression of the WRI1 target genes, and consequently increased the oil content by 4.3-4.9 fold when compared with the controls, and <i>RcWRI1-B</i> appeared to be more active than <i>RcWRI1-A</i>. Both <i>RcWRI1-A</i> and <i>RcWRI1-B</i> can be used as a key transcriptional regulator to enhance fatty acid and oil biosynthesis in leafy biomass.