Isolation of two putative homologues of PISTILLATA and AGAMOUS from Alpinia oblongifolia (Zingiberaceae) and characterization of their expression

We cloned the cDNAs of AG- and PI-like genes from a young inflorescence cDNA library of Alpinia oblongifolia. Two MADS-box related clones were repeatedly isolated: A. oblongifolia PISTILLATA (AoPI) and A. oblongifolia AGAMOUS (AoAG). AoPI cDNA is 841 bp long including the poly-A tail instead of 826 bp long and encodes a 208 amino acid peptide. AoAG is 971 bp long and encodes a 229 amino acid peptide. Sequence comparisons indicated that AoPI and AoAG are very similar to PI and AG homologues, respectively. Phylogenetic analyses showed that AoPI belongs to the PI group and AoAG belongs to the AG group of genes. In situ hybridization demonstrated that the AoPI gene is expressed in petals and stamen throughout the process of flower development, and that the AoAG gene is expressed in stamen throughout flower development and in carpels in the early stages of development. AoAG is also expressed in the ovules. The expression patterns of AoPI and AoAG are generally consistent with those of the floral homeotic PI- and AG-like genes in other plant species; these specify the identities of the second and third whorls, and third and fourth whorls, respectively. Therefore, in A. oblongifolia, AoPI is a B-functional gene and AoAG is a C-functional gene. The conservation and diversification of the expression of both genes are discussed.