Naturally occurring flower mutation in offspring of a large fruited raspberry chance seedling
A red raspberry population was established from an open pollination of a large fruited chance seedling. Subsequently, three different floral phenotypes were observed in this population. Type 1 is equivalent to the wild type raspberry flower phenotype with five sepals and petals, with stamens and carpels present. Type 2 has six to eight sepals and petals, with stamens and carpels present. Type 3 has sepaloid and carpeloid structures, but no petals and stamens. Floral phenotype as well as fruit weight, length and drupelet number was evalu-ated for this population. Type 1 and 3 fruits are smaller and have a smaller number of drupelets than type 2 fruits. The ABC-model of flower development suggests that type 3 phenotypes are caused by perturbation of class B genes. In other Rosaceae plant species similar phenotypes are caused by mutation of the PISTILLATA (PI) gene, as APETALA3 has several homologs and is thus more robust against impairment. We defined MADS- and K-box containing genes from Rubus occidentalis (black raspberry) by Hidden Markov Model search. A neigh-bor joining tree was produced through amino acid sequence homology. Alt-hough no homolog for PI was found ini-tially, a BLAST search detected a non-an-notated sequence with high homology to Arabidopsis thaliana PI. A PCR with type 1 and 3 genomic DNA was performed. Since fragments were of the same size, we speculated that the dif-ference between type 1 and type 3 is on the sequence level. Indeed, cloning and sequencing of type 1 and 3 cDNA and type 3 gDNA revealed that type 1 trans-lates into 212 and type 3 into 207 amino acids. Both sequences differ in 54 amino acids. This makes impairment of PISTIL-LATA in type 3 plants a plausible explana-tion for type 3 phenotypes. An RT-PCR on type 1 and type 3 whole flowers and individual whorls was con-ducted. There was substantial reduction of PI-levels in type 3 samples. As ex-pected, whole flower as well as petals and stamens displayed the highest PI-lev-els. Moreover, we plan complementation of the A. thaliana pi-1 mutant with type 1 and type 3 alleles. To analyze the impact on fruit size, we crossed type 1 and type 3 plants with two tester cultivars. Fruit size evaluation will be carried out in the F1. This project will also lead to the develop-ment of molecular markers for fruit size, which might benefit current raspberry breeding programs.