High-quality maple genome reveals duplication-facilitated leaf color diversity

Abstract

Acer truncatum is a horticultural tree species with individuals that display either yellow or red leaves in autumn, giving it high ornamental and economic value. 'Lihong' of A. truncatum is an excellent cultivar due to its characteristic of having autumn leaves that turn a bright and beautiful shade of red, while its closely related cultivar 'Bunge' does not. However, the molecular mechanism underlying the color change in the cultivar 'Lihong' is still unclear. Here, we assembled a high-quality genome sequence of Acer truncatum 'Lihong' (genome size = 688 Mb, scaffold N50 = 9.14 Mb) with 28,438 protein-coding genes predicted. Through comparative genomic analysis, we found that 'Lihong' had experienced more tandem duplication events although it’s a high degree of collinearity with 'Bunge'. Especially, the expansion of key enzymes in the anthocyanin synthesis pathway was significantly uneven between the two varieties, with 'Lihong' genome containing a significantly higher number of tandem/dispersed duplication key genes. Further transcriptomic, metabolomic, and molecular functional analyses demonstrated that several UFGT genes, mainly resulting from tandem/dispersed duplication, followed by the promoter sequence variation, may contribute greatly to the leaf color phenotype, which provides new insights into the mechanism of divergent anthocyanin accumulation process in the 'Lihong' and 'Bunge' with yellow leaves in autumn. Further, constitutive expression of two UFGT genes, which showed higher expression in 'Lihong', elevated the anthocyanin content. We proposed that the small-scale duplication events could contribute to phenotype innovation.