Genetic Basis of <scp>UV</scp> Bullseye Size Variations in Turnip Rape ( <i>Brassica rapa</i> subsp. <i>oleifera</i> )

Floral ultraviolet (UV) patterns are visible to bee pollinators and can affect crop yields by impacting pollinator visitation. However, the mechanisms underlying the intraspecific variations of UV bullseye size remain largely unknown. We analyse the ecological consequences and genetic basis of floral UV bullseye size variation in an important oil crop at high altitudes, Brassica rapa subsp. oleifera (turnip rape). Flowers with larger UV bullseye attract more bees and produce more seeds. The transcription factor BrobZIP16 was newly identified as a key determinant of large UV bullseye, supported by evidence of its high expression and selective sweeps in plants with larger UV bullseye. BrobZIP16 regulates UV bullseye size by interacting with the known regulator BroMYB111 in the flavonoid biosynthetic pathway and accumulating UV-absorbing flavonols. Our results reveal the mechanisms underlying intraspecific UV bullseye size variations, and such 'cryptic' large bullseye can be targeted in molecular breeding to increase oilseed production.