Tracking the 'Bud Bloomer Gene' in Calluna vulgaris

Calluna vulgaris is a woody ornamental of rising popularity in northern Europe. It realizes increasing profits due the so called 'bud flowering' mutants. The 'bud bloomers' are characterized by three traits: loss of stamens, transformation from petals to petaloid sepals and developmental persistence in the bud stage. Although the flower architecture is highly relevant for their value as ornamental crops, molecular mechanisms of flower development have rarely been studied in ornamentals before. We aim to identify the genetic basis of the 'bud flowering' trait in C. vulgaris. A classical genetic approach revealed recessive monogenic inheritance of this character. By morphological and histological methods as well as by gene expressions studies of two homeotic genes controlling flower development organ identity of perianth organs was determined. From Arabidopsis the ABCDE model has been deduced giving precise prospects of MADS-Box transcription factors controlling flower organ identity. Since in the' bud flowering' phenotype of C. vulgaris affected organs are petals and stamens a B gene mutation might be anticipated. Contrary to this hypothesis is the observation that in model plants the alteration in B gene activity causes the transformation from petals into sepals and from stamens into carpels but not the loss of stamens. So far the ABCDE model fails to explain the unique flower architectures of C. vulgaris 'bud bloomers'. But a transcriptome analyses by RNASeq comparing the expression of 11,128 isotigs in wild-type and bud-blooming flowers indicated a MADS-Box gene as possible candidate for the 'bud bloomer gene' in C. vulgaris.