Site-Directed Mutagenesis of the Carotenoid Isomerase Gene BnaCRTISO Alters the Color of Petals and Leaves in Brassica napus L.

Abstract

The diversity of petal and leaf color can improve the ornamental value of rapeseed and promote the development of agriculture and tourism. The two copies of carotenoid isomerase gene (<i>BnaCRTISO</i>) in <i>Brassica napus</i> (<i>BnaA09.CRTISO</i> and <i>BnaC08.CRTISO</i>) was edited using the CRISPR/Cas9 system in the present study. The mutation phenotype of creamy white petals and yellowish leaves could be recovered only in targeted mutants of both <i>BnaCRTISO</i> functional copies, indicating that the redundant roles of <i>BnaA09.CRTISO</i> and <i>BnaC08.CRTISO</i> are vital for the regulation of petal and leaf color. The carotenoid content in the petals and leaves of the <i>BnaCRTISO</i> double mutant was significantly reduced. The chalcone content, a vital substance that makes up the yellow color, also decreased significantly in petals. Whereas, the contents of some carotenes (lycopene, α-carotene, γ-carotene) were increased significantly in petals. Further, transcriptome analysis showed that the targeted mutation of <i>BnaCRTISO</i> resulted in the significant down-regulation of important genes <i>BnaPSY</i> and <i>BnaC4H</i> in the carotenoid and flavonoid synthesis pathways, respectively; however, the expression of other genes related to carotenes and xanthophylls synthesis, such as <i>BnaPDS3</i>, <i>BnaZEP</i>, <i>BnaBCH1</i> and <i>BCH2</i>, was up-regulated. This indicates that the molecular mechanism regulating petal color variation in <i>B. napus</i> is more complicated than those reported in <i>Arabidopsis</i> and other <i>Brassica</i> species. These results provide insight into the molecular mechanisms underlying flower color variation in rapeseed and provides valuable resources for rapeseed breeding.