Molecular Characterization of Rose Flavonoid Biosynthesis Genes and Their Application in Petunia

Haplotype-resolved genome assembly of the diploid Rosa chinensis provides insight into the mechanisms underlying key ornamental traits

Roses are consistently ranked at the forefront in cut flower production. Increasing demands of market and changing climate conditions have resulted in the need to further improve the diversity and quality of traits. However, frequent hybridization leads to highly heterozygous nature, including the allelic variants. Therefore, the absence of comprehensive genomic information leads to them making it challenging to molecular breeding. Here, two haplotype-resolved chromosome genomes for Rosa chinensis 'Chilong Hanzhu' (2n = 14) which is high heterozygous diploid old Chinese rose are generated. An amount of genetic variation (1,605,616 SNPs, 209,575 indels) is identified. 13,971 allelic genes show differential expression patterns between two haplotypes. Importantly, these differences hold valuable insights into regulatory mechanisms of traits. RcMYB114b can influence cyanidin-3-glucoside accumulation and the allelic variation in its promoter leads to differences in promoter activity, which as a factor control petal color. Moreover, gene family expansion may contribute to the abundance of terpenes in floral scents. Additionally, RcANT1, RcDA1, RcAG1 and RcSVP1 genes are involved in regulation of petal number and size under heat stress treatment. This study provides a foundation for molecular breeding to improve important characteristics of roses.

Integrated metabolome and transcriptome analysis of the anthocyanin biosynthetic pathway in relation to color mutation in miniature roses

BACKGROUND

Roses are famous ornamental plants worldwide. Floral coloration is one of the most prominent traits in roses and is mainly regulated through the anthocyanin biosynthetic pathway. In this study, we investigated the key genes and metabolites of the anthocyanin biosynthetic pathway involved in color mutation in miniature roses. A comparative metabolome and transcriptome analysis was carried out on the Neptune King rose and its color mutant, Queen rose, at the blooming stage. Neptune King rose has light pink colored petals while Queen rose has deep pink colored petals.

RESULT

A total of 190 flavonoid-related metabolites and 38,551 unique genes were identified. The contents of 45 flavonoid-related metabolites, and the expression of 15 genes participating in the flavonoid pathway, varied significantly between the two cultivars. Seven anthocyanins (cyanidin 3-O-glucosyl-malonylglucoside, cyanidin O-syringic acid, cyanidin 3-O-rutinoside, cyanidin 3-O-galactoside, cyanidin 3-O-glucoside, peonidin 3-O-glucoside chloride, and pelargonidin 3-O-glucoside) were found to be the major metabolites, with higher abundance in the Queen rose. Thirteen anthocyanin biosynthetic related genes showed an upregulation trend in the mutant flower, which may favor the higher levels of anthocyanins in the mutant. Besides, eight TRANSPARENT TESTA 12 genes were found upregulated in Queen rose, probably contributing to a high vacuolar sequestration of anthocyanins. Thirty transcription factors, including two MYB and one bHLH, were differentially expressed between the two cultivars.

CONCLUSIONS

This study provides important insights into major genes and metabolites of the anthocyanin biosynthetic pathway modulating flower coloration in miniature rose. The results will be conducive for manipulating the anthocyanin pathways in order to engineer novel miniature rose cultivars with specific colors.

Graft-accelerated virus-induced gene silencing facilitates functional genomics in rose flowers

Rose has emerged as a model ornamental plant for studies of flower development, senescence, and morphology, as well as the metabolism of floral fragrances and colors. Virus-induced gene silencing (VIGS) has long been used in functional genomics studies of rose by vacuum infiltration of cuttings or seedlings with an Agrobacterium suspension carrying TRV-derived vectors. However, VIGS in rose flowers remains a challenge because of its low efficiency and long time to establish silencing. Here we present a novel and rapid VIGS method that can be used to analyze gene function in rose, called 'graft-accelerated VIGS', where axillary sprouts are cut from the rose plant and vacuum infiltrated with Agrobacterium. The inoculated scions are then grafted back onto the plants to flower and silencing phenotypes can be observed within 5 weeks, post-infiltration. Using this new method, we successfully silenced expression of the RhDFR1, RhAG, and RhNUDX1 in rose flowers, and affected their color, petal number, as well as fragrance, respectively. This grafting method will facilitate high-throughput functional analysis of genes in rose flowers. Importantly, it may also be applied to other woody species that are not currently amenable to VIGS by conventional leaf or plantlet/seedling infiltration methods.

Genetics and genomics of flower initiation and development in roses

Roses hold high symbolic value and great cultural importance in different societies throughout human history. They are widely used as garden ornamental plants, as cut flowers, and for the production of essential oils for the perfume and cosmetic industries. Domestication of roses has a long and complex history, and the rose species have been hybridized across vast geographic areas such as Europe, Asia, and the Middle East. The domestication processes selected several flower characters affecting floral quality, such as recurrent flowering, double flowers, petal colours, and fragrance. The molecular and genetic events that determine some of these flower characters cannot be studied using model species such as Arabidopsis thaliana, or at least only in a limited manner. In this review, we comment on the recent development of genetic, genomic, and transcriptomic tools for roses, and then focus on recent advances that have helped unravel the molecular mechanisms underlying several rose floral traits.

Flower proteome: changes in protein spectrum during the advanced stages of rose petal development

Flowering is a unique and highly programmed process, but hardly anything is known about the developmentally regulated proteome changes in petals. Here, we employed proteomic technologies to study petal development in rose (Rosa hybrida). Using two-dimensional polyacrylamide gel electrophoresis, we generated stage-specific (closed bud, mature flower and flower at anthesis) petal protein maps with ca. 1,000 unique protein spots. Expression analyses of all resolved protein spots revealed that almost 30% of them were stage-specific, with ca. 90 protein spots for each stage. Most of the proteins exhibited differential expression during petal development, whereas only ca. 6% were constitutively expressed. Eighty-two of the resolved proteins were identified by mass spectrometry and annotated. Classification of the annotated proteins into functional groups revealed energy, cell rescue, unknown function (including novel sequences) and metabolism to be the largest classes, together comprising ca. 90% of all identified proteins. Interestingly, a large number of stress-related proteins were identified in developing petals. Analyses of the expression patterns of annotated proteins and their corresponding RNAs confirmed the importance of proteome characterization.