Isolation and Characterization of Three MADS-box Genes from Alpinia hainanensis (Zingiberaceae)

Three complementary DNA clones, AhMADS5, AhMADS6, and AhMADS8 were isolated from the young inflorescences of Alpinia hainanensis. Sequence comparisons and phylogenetic analyses indicated that AhMADS5 and AhMADS8 are highly homologous to AP3 and PI family, respectively, and AhMADS6 is an AG homologue. In situ hybridization analyses showed that AhMADS5 and AhMADS8 genes are expressed in the second and third whorls, whereas, the AhMADS6 signal is present in the third and fourth whorls. The expression patterns of AhMADS5, AhMADS8, and AhMADS6 genes are very similar to those of AP3-, PI-, and AG-like genes in other plant species, respectively. These results suggest that while AhMADS5 and AhMADS8 belong to the B-class MADS-box gene family, AhMADS6 belongs to a different category, the C-class MADS-box gene family. Present studies strongly support the hypothesis that the labellum of A. hainanensis originated from stamens.