M. Abe et al., Identification of a cis-regulatory element for L1 layer-specific gene expression, which is targeted by an L1-specific homeodomain protein, PLANT J, 26(5), 2001, pp. 487-494
The Arabidopsis thaliana PROTODERMAL FACTOR1 (PDF1) gene encoding a putativ
e extracellular proline-rich protein is exclusively expressed in the L1 lay
er of shoot apices and the protoderm of organ primordia. In order to identi
fy essential cis-regulatory sequences required for the L1 layer-specific ex
pression, a series of 5' deletions of the PDF1 promoter were fused to the b
eta -glucronidase (GUS) gene and introduced into Arabidopsis plants. Our an
alysis revealed that the minimum region necessary to confer L1-specific exp
ression of PDF1 is confined within a 260-bp fragment upstream of the transc
ription start site. We identified an 8-bp motif in this region that is cons
erved between promoter regions of all the L1-specific genes so far cloned,
and we designated it the L1 box. Electrophoretic mobility shift assays demo
nstrated that the L1-specific homeodomain protein ATML1 can bind to the L1
box sequence in vitro. The GUS expression in transgenic plants disappeared
when a mutation that abolishes binding of ATML1 was introduced into the PDF
1 /1 box sequence of the construct. These results suggest that the L1 box p
lays a crucial role in the regulation of PDF1 expression in L1 cells and th
at ATML1 could cooperate to drive L1-specific expression.