THE ARABIDOPSIS AGL9 MADS BOX GENE IS EXPRESSED IN YOUNG FLOWER PRIMORDIA

MADS box genes are likely involved in many different steps of plant de velopment, since their RNAs accumulate in a wide variety of tissues, i ncluding roots, stems, leaves, flowers and embryos. In flowers, MADS b ox genes regulate the early step of specifying floral meristem identit y as well as the later step of determining the fate of floral organ pr imordia. Here we describe the isolation and characterization of a new MADS box gene from Arabidopsis, AGL9. Sequence analyses indicate that AGL9 represents the putative ortholog of the FBP2 and TM5 genes from p etunia and tomato, respectively. In situ hybridization analyses show t hat AGL9 RNA begins to accumulate after the onset of expression of the floral meristem identity genes, but before the activation of the orga n identity genes. These data indicate that AGL9 functions early in flo wer development to mediate between the interaction of these two classe s of genes. Later in flower development, AGL9 RNA accumulates in petal s, stamens, and carpels, suggesting a role for AGL9 in controlling the development of these organs.