Abstract
Gene mutation is a common phenomenon in nature that often leads to phenotype differences, such as the variations in flower color that frequently occur in roses. With the aim of revealing the genomic information and inner mechanisms, the differences in the levels of both transcription and secondary metabolism between a pair of natural rose mutants were investigated by using hybrid RNA-sequencing and metabolite analysis. Metabolite analysis showed that glycosylated derivatives of pelargonidin, e.g., pelargonidin 3,5 diglucoside and pelargonidin 3-glucoside, which were not detected in white flowers (Rosa ‘Whilte Mrago Koster’), constituted the major pigments in pink flowers. Conversely, the flavonol contents of petal, such as kaempferol-3-glucoside, quercetin 3-glucoside, and rutin, were higher in white flowers. Hybrid RNA-sequencing obtained a total of 107,280 full-length transcripts in rose petal which were annotated in major databases. Differentially expressed gene (DEG) analysis showed that the expression of genes involved in the flavonoid biosynthesis pathway was significantly different, e.g., CHS, FLS, DFR, LDOX, which was verified by qRT-PCR during flowering. Additionally, two MYB transcription factors were found and named RmMYBAN2 and RmMYBPA1, and their expression patterns during flowering were also analyzed. These findings indicate that these genes may be involved in the flower color difference in the rose mutants, and competition between anthocyanin and flavonol biosynthesis is a primary cause of flower color variation, with its regulation reflected by transcriptional and secondary metabolite levels.
Highlights
Rose is one of the most important ornamental woody plants belonging to the genus Rosa of the Rosaceae family, and its original species and cultivar present diverse flowers, delicate fragrances, and ornamental traits
Two MYB transcription factors were found and named RmMYBAN2 and RmMYBPA1, and their expression patterns during flowering were analyzed. These findings indicate that these genes may be involved in the flower color difference in the rose mutants, and competition between anthocyanin and flavonol biosynthesis is a primary cause of flower color variation, with its regulation reflected by transcriptional and secondary metabolite levels
These findings indicate that the rose varieties exhibited a wide variation of pigments in their petals, including cyanidin, peonidin, and pelargonidin, as well as other pigments; pelargonidin 3,5 diglucoside and pelargonidin 3-glucoside were the main pigments in the petal of Rosa ‘Margo Koster’, and a small quantity of cyanidin 3,5-diglucoside and peonidin 3,5-diglucoside were detected in Rosa ‘Margo Koster’ (Table 5, Figure 5)
Summary
Rose is one of the most important ornamental woody plants belonging to the genus Rosa of the Rosaceae family, and its original species and cultivar present diverse flowers, delicate fragrances, and ornamental traits. Over the past 5000 years, over 30,000 cultivated varieties have been selected and bred by the hybridization of certain original species and their cultivars, which are distributed across China, Europe, and the Middle East. Frequent interspecies crossbreeding between cultivated varieties and polyploid wild species has made the classification of roses very difficult, and these kinds of extensive hybridizations have led to the diversification of floral traits [3]. Floral traits have always attracted attention from breeders and scientists, and flower phenotypes result from the complex interaction of molecular and cellular processes with environmental factors [4]. An understanding of the inner genetic regulation and control mechanisms is of interest to Plants 2019, 8, 267; doi:10.3390/plants8080267 www.mdpi.com/journal/plants
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