Switching of self-incompatibility in resynthesized Arabidopsis allotetraploids. (a) Flower morphology of self-compatible A. suecica. (b) Self-incompatible A. arenosa and (c and d) two self-compatible synthetic allotetraploid lines. The altered flower organs (elongated stigma and relatively short stamens) in the synthetic allotetraploids (c and d) may contribute to a low fertility without manual pollination. Size bars (5 mm) are the same in (a) and (b) or in (c) and (d). (e) Diagram of cytoplasmic and nuclear interactions in resynthesized allotetraploids (Allos, 2n = 4x = 26). T or A and tt or aa denote cytoplasm and nuclear genomes, respectively. The cytoplasmic-nuclear genotypes for autotetraploid A. thaliana (At4) are Ttttt, tetraploid A. arenosa (Aa), Aaaaa; and allotetraploids, and either Taatt or Aaatt in reciprocal crosses. Blue and gray indicate A. thaliana and A. arenosa cytoplasms, whereas green, red, and yellow indicate nuclear genomes of A. thaliana, A. arenosa, and allotetraploids, respectively. A. thaliana is self-compatible (SC), whereas A. arenosa is self-incompatible (SI). The resynthesized allotetraploids (Allos) are SC. Fertile seeds are readily obtained from the cross using A. thaliana as a maternal parent and A. arenosa as a pollen donor, and the reciprocal cross is usually unsuccessful (31).