Evidence for factors regulating transfer cell-specific expression in maize endosperm.
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.
Hueros
G
G
MPI für Züchtungsforschung, Köln, Germany.
Royo
J
J
Maitz
M
M
Salamini
F
F
Thompson
R D
RD
D000595:Amino Acid Sequence; D001692:Biological Transport / Q000235:genetics; D004179:Cobra Cardiotoxin Proteins / Q000235:genetics; D004268:DNA-Binding Proteins / Q000378:metabolism*; D023082:Defensins; D015870:Gene Expression; D017343:Genes, Plant; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D012639:Seeds / Q000166:cytology / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D014018:Tissue Distribution; D003313:Zea mays / Q000166:cytology / Q000235:genetics*
C402653:BETL-2 protein, Zea mays; C402654:BETL-3 protein, Zea mays; C402655:BETL-4 protein, Zea mays; D004179:Cobra Cardiotoxin Proteins; D004268:DNA-Binding Proteins; D023082:Defensins; D009687:Nuclear Proteins; D010940:Plant Proteins