DIP: a member of the MIP family of membrane proteins that is expressed in mature seeds and dark-grown seedlings of Antirrhinum majus

DiP , a gene from Antirrhinum majus , which encodes a protein with striking homology to other integral membrane proteins, was cloned. The gene was specifically expressed in mature seeds and during seedling germination, particularly in cotyledons of seedlings grown in the dark. The deduced product, called DiP, for dark intrinsic protein, shows strong homology with the MIP family of channel transporters which include; the bovine major intrinsic protein (MIP), the Escherichia coli glycerol facilitator (GlpF), the peribacteroid nodulin-26 (Nod26), and the tonoplast protein from kidney bean (TIP). DiP is most similar to other plant members of this family, and in particular to the tobacco protein TobRB7 which is expressed specifically in roots. However, the expression pattern of diP suggests that its product is functionally more similar to the tonoplast intrinsic protein from kidney bean since it is most highly expressed in the cotyledons of germinating seedlings, before the cells undergo expansion growth and become photosynthetic.