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Evidence for factors regulating transfer cell-specific expression in maize endosperm
Authors:Hueros  Gregorio  Royo  Joaquin  Maitz  Monika  Salamini  Francesco  Thompson  Richard D
Institution:(1) MPI für Züchtungsforschung, Carl-von-Linné Weg 10, 50829 Köln, Germany;(2) Dpto. Biología Celular y Genetica, University Alcala, 28871 Alcala de Henares, Spain
Abstract:In maize, a layer of basal endosperm cells adjacent to the pedicel is modified for a function in solute transfer. Three genes specifically expressed in this region, termed the basal endosperm transfer layer (BETL-2 to -4), were isolated by differential hybridization. BETL-2 to -4 are coordinately expressed in early and mid-term endosperm development, but are absent at later stages. BETL-2 to -4 coding sequences all predict small (<100 amino acids), secreted, cysteine-rich polypeptides which lack close relatives in current database accessions. BETL-3 and BETL-1 display some sequence similarities with each other and to plant defensins. BETL-2 to -4 promoter regions were isolated and compared, revealing the presence of a promoter-proximal microsatellite repeat as the most highly conserved sequence element in each sequence. Electrophoretic mobility shift assays (EMSA) showed that specific BETL-2 to -4 promoter fragments competed for binding to the same DNA-binding activity in nuclear extracts prepared from maize endosperm. Although BETL-2 to -4 are only expressed in basal endosperm cells, the DNA-binding activities detected were of two types: distal endosperm-specific, or present in both basal and distal endosperm extracts. On the basis of these findings, a model to account for the coordinate regulation of BETL genes in endosperm cells is proposed.
Keywords:BETL  endosperm  maize  promoter  transfer cell
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