The structure and expression of SEPALLATA-like genes in Asparagus species (Asparagaceae)

MADS-box genes encode transcriptional regulators that are critical for a number of developmental processes. In the MADS-box gene family, the SEPALLATA (SEP) gene subfamily plays an important role in controlling the development of floral organs in flowering plants. To understand the molecular mechanisms of floral development in Asparagus, we isolated and characterized several SEP-like genes from dioecious Asparagus officinalis and hermaphrodite A. virgatus: AOMADS1, AOMADS2, AOMADS3, and AVMADS1, AVMADS2, AVMADS3, respectively. Through alignment of the predicted amino acid sequences of various SEP-like genes, we defined three characteristic motifs in the C-terminal region of the genes: SEP motif I, SEP/AGL6 motif, and SEP motif II. Of the genes we isolated, AOMADS3 and AVMADS3 had lost the SEP motif II. Phylogenetic analysis revealed that AOMADS1, AOMADS2, AVMADS1, and AVMADS2 were closely related to SEP3 from Arabidopsis, whereas AOMADS3 and AVMADS3 were classified in different clade which is far related to SEP3 gene. Northern hybridization and RT-PCR showed that three SEP-like genes in A. officinalis were specifically expressed in the flower buds. In addition, PCR RFLP showed that there was no significant difference in the amount of transcripts of AOMADS1 and AOMADS2. These results suggest that AOMADS1 and AOMADS2 may be redundant genes. In contrast, the expression of AOMADS3 was weaker than that of AOMADS1 or AOMADS2, suggesting that the function of AOMADS3 may be different than that of AOMADS1 or AOMADS2.