Mechanism behind Petal Color Mutation Induced by Heavy-Ion-Beam Irradiation of Recalcitrant Chrysanthemum Cultivar

Abstract

White chrysanthemum flowers frequently mutate to yellow, but such mutation is rare in ‘Jimba’. We found a bud sport (BS) of ‘Jimba’ with a faintly yellow flower. By applying heavy-ion-beam radiation to the BS, we obtained mutants with a pale yellow flower (IB-1 lines). We irradiated those and obtained mutants with much deeper yellow flowers (IB-2 lines). Decreased expression of carotenoid cleavage dioxygenase 4 (CmCCD4a) was well correlated with increased carotenoid content in petals of the mutants. CmCCD4a comprises a small gene family in the ‘Jimba’ genome; at least 4 homologs were expressed in the petals of wild-type ‘Jimba’ and BS, but only 3 were expressed in the petals of IB-1 and only 1 in IB-2. We hypothesize that the decreased number of CmCCD4a homologs caused by irradiation is responsible for the decrease in expression.