SBP-Box Transcription Factor JcSPL9 Regulates Both Seed Yield and Oil Content in the Biofuel Plant Jatropha curcas

Jatropha curcas is a promising feedstock for biodiesel and bio-jet fuels production; however, its seed yield is constrained by limited inflorescences. SPL9 is a member of the SBP-box gene family that promotes the juvenile-to-adult phase transition. Accumulating evidence demonstrated that the miR156/SPL module plays important roles in regulating diverse plant developmental processes. Here, we reveal that JcSPL9 regulates both seed yield and oil content in Jatropha. JcSPL9 is highly expressed in fruits and upregulated with age in Jatropha. Overexpression of miR156-resistant JcSPL9 (rJcSPL9) significantly increased seed yield and oil content, whereas overexpression of JcmiR156a had the opposite effects. The highest seed yield in rJcSPL9 transgenic plants was 80.76% greater than that in the WT plants, with a concomitant 12.6% increase in seed oil content. Correspondingly, JcmiR156a transgenic plants displayed 51.67% lower seed yield and 8.28% lower seed oil content compared to WT. Additionally, seed oil fatty acid composition was significantly altered in both rJcSPL9 and JcmiR156a transgenic Jatropha and Arabidopsis, as well as in Arabidopsis spl9 mutants. The key oil biosynthesis genes, including JcWRI1, JcDGAT1, JcDGAT2, and JcOLEOSIN, were upregulated in rJcSPL9 transgenic seeds but downregulated in JcmiR156a transformants. This study provides the first evidence that the miR156/SPL9 module regulates lipid accumulation and fatty acid biosynthesis in seeds. These results highlight SPL9 as a promising target for enhancing oil yield and quality in Jatropha and other oilseed crops.