The potato MADS-box gene POTM1 is a member of the SQUA-like family of plant MADS-box genes. The amino acid sequence of POTM1 most closely matches the sequence of PFG (Petunia Flowering Gene), a petunia MADS-box gene involved in the transition from vegetative to reproductive development. To examine the likely role of POTM1 in potato reproductive tissue, in situ hybridizations were performed on sections of the potato shoot apex at various stages during the transition to flowering. Scanning electron micrographs provide a reference for each stage to illustrate the progression from vegetative meristem to inflorescence meristem and floral organs. POTM1 mRNA accumulates in vegetative, inflorescence and floral meristems. Transcripts are present in petal primordia during the later stages of petal development and they accumulate later during floral development inside the stamens and carpels, but not in carpel walls. This widespread pattern of mRNA accumulation is unique among the SQUA-like genes and indicates that POTM1 is active during a variety of stages of development, and may function in regulating cell determination in transitional phases of both vegetative and floral meristems.