title: The C-terminal sequence of LMADS1 is essential for the formation of homodimers for B function proteins.
abstract: LMADS1, a lily (Lilium longiflorum) AP3 orthologue, contains the complete consensus sequence of the paleoAP3 (YGSHDLRLA) and PI-derived (YEFRVQPSQPNLH) motifs in the C-terminal region of the protein. Interestingly, through yeast two-hybrid analysis, LMADS1 was found to be capable of forming homodimers. These results indicated that LMADS1 represents an ancestral form of the B function protein, which retains the ability to form homodimers in regulating petal and stamen development in lily. To explore the involvement of the conserved motifs in the C-terminal region of LMADS1 in forming homodimers, truncated forms of LMADS1 were generated, and their ability to form homodimers was analyzed using yeast two-hybrid and electrophoretic mobility shift assay. The ability of LMADS1 to form homodimers decreased once the C-terminal paleoAP3 motif was deleted. When both paleoAP3 and PI-derived motifs were deleted, the ability of LMADS1 to form homodimers was completely abolished. This result indicated that although the paleoAP3 motif promotes the formation of LMADS1 homodimers, the PI-derived motif is essential. Deletion analysis indicated that two amino acids, RV, of the 5 final amino acids, YEFRV, in the PI-derived motif are essential for the formation of homodimers. Further, point mutation analysis indicated that amino acid Val was absolutely necessary, whereas residue Arg played a less important role in the formation of homodimers. Furthermore, Arabidopsis AP3 was able to form homodimers once its C-terminal region was replaced by that of LMADS1. This result indicated that the C-terminal region of LMADS1 is responsible and essential for homodimer formation of the ancestral form of the B function protein.
authors.affiliation: Graduate Institute of Biotechnology, National Chung Hsing University, Taichung, Taiwan 40227, Republic of China.
authors.forename: Tsai-Yu
authors.initials: TY
authors.lastname: Tzeng
authors.forename: Hsin-Ching
authors.initials: HC
authors.lastname: Liu
authors.forename: Chang-Hsien
authors.initials: CH
authors.lastname: Yang
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D001483:Base Sequence; D018076:DNA, Complementary / Q000378:metabolism; D019281:Dimerization; D017353:Gene Deletion; D027762:Lilium / Q000378:metabolism*; D026161:MADS Domain Proteins / Q000737:chemistry* / Q000502:physiology*; D008969:Molecular Sequence Data; D017354:Point Mutation; D017434:Protein Structure, Tertiary; D020798:Two-Hybrid System Techniques; D014633:Valine / Q000737:chemistry
chemical_list: D018076:DNA, Complementary; D026161:MADS Domain Proteins; D014633:Valine