Comparative transcriptomic analysis to postulate the generation of variegated leaves in Bougainvillea peruviana ‘Thimma’

The underlying mechanism of leaf coloration remains blank in Bougainvillea peruviana 'Thimma', which has high ornamental value in urban landscape. In this study, the variegated leaves were comprehensively characterized. Compared to the green leaves, the yellow sectors of variegated leaves had severely disrupted chloroplasts and ruptured thylakoid membranes. The chloroplast number was lower in the yellow sectors of variegated leaves. The chlorophyll and carotenoid contents were extremely lower in the yellow sectors of variegated leaves. Besides, the contents of three key chlorophyll precursors, protoporphyrin IX (Proto IX), magnesium protoporphyrin IX (Mg-Proto IX), and protochlorophyllide (Pchlide), were significantly decreased in the yellow sectors of variegated leaves. The abscisic acid (ABA) content was higher in the yellow sectors of variegated leaves. Moreover, through comparative transcriptome analysis of mature completely green leaves and yellow sectors of variegated leaves, a total of 951 differentially expressed genes (DEGs) were identified. Further annotation analysis indicated that DEGs involved in chlorophyll biosynthesis and the development of chloroplast were downregulated in yellow sectors of variegated leaves, which were likely the main causes of the yellow color phenotype. Additionally, two DEGs were enriched in the ABA biosynthesis, which might inspire future research on correlation between leaf color and hormone. These findings will provide novel insights for leaf coloration regulation in B. peruviana.