AN RNA MARKER FOR EPIDERMAL-CELL TYPE AND DIFFERENTIATION

This paper summarizes our recent work on the regulation and expression of a gene family encoding a vegetative homologue (Blec) of the pea se ed lectin. Blec is encoded by a multigene family whose members share 4 0-50% identity with other legume lectins. Blec RNA is highly expressed within specific phases of epidermal cell development, it accumulates specifically in meristematic epidermal cells of vegetative and floral organs, but is undetectable in protodermal cells that bound vegetative or floral meristems. Furthermore, during early vegetative and floral primordia development Blec accumulates mainly on the abaxial epidermis and is undetectable on the adaxial or inner surface of such organs. T he accumulation of Blec thereby not only defines the epidermis, but al so specific stages and positions of epidermal tissue during organ deve lopment. These observations are discussed with a view to further defin ing the regulatory events involved in epidermal differentiation. As a first step, a Blec genomic clone has been expressed in alfalfa RegenSY . Preliminary analysis shows that, as in pea, Blec is expressed in alf alfa RegenSY in an apex specific manner.