Genetic determinants of the flower color transition trait in autotetraploid rose populations

Some roses exhibit a unique phenotype that we call flower color transition. Roses that have this phenotype have flowers with petals that transition from a light yellow to a dark pink/red color as the flower ages. This is an attractive commercial feature for the industry, but also an intriguing phenotype to better understand the genetics of rose flower color patterning. Two tetraploid garden rose F1 populations segregating for the flower color transition phenotype were used for this study. To better understand the genetic basis of this trait, we conducted a quantitative trait locus (QTL) mapping study. Our analysis showed that multiple genetic factors control flower color and the flower color transition trait. We identified 25 and 19 QTL for all measured color parameters (L*, a*, and b* color spaces, chroma, and hue) and measures of flower color transition (DEvar, DEmm, and Trans.score) in the Stormy Weather x Brite Eyes (SWxBE) and Brite Eyes x My Girl (BExMG) populations, respectively. Most QTL for flower color and the flower color transition trait clustered in coincident locations on LGs 2, 3, 4, 6, and 7. The QTL with the largest effects were found in LG 4 with proportion of variance explained (PVE) values ranging from 18 to 34 %, LG 6 with PVEs ranging from 15 to 47 %, and LG 7 with PVEs ranging 13 to 47 %. These were followed by QTL in LGs 3 (PVEs ranging from 11–21 %) and 2 (PVEs ranging from 7–29 %). In addition, the locations of QTL coincided with the locations of structural genes involved in the flavonoid biosynthetic pathway and transcription factors regulating them. This study suggests that the regulation of the color transition phenotype is complex and involves the interplay of multiple factors that either promote or inhibit flower pigmentation. This study also paves the way for studies to identify molecular mechanisms that affect flower color transition in roses, which in turn, may guide strategies to develop roses with unique pigmentation patterns.