Yh. Yin et al., PROMOTER ELEMENTS REQUIRED FOR PHLOEM-SPECIFIC GENE-EXPRESSION FROM THE RTBV PROMOTER IN RICE, Plant journal, 12(5), 1997, pp. 1179-1188
Previous studies indicated that a DNA fragment comprising nucleotides
(nt) -164 to +45 of the RTBV promoter is sufficient to drive phloem-sp
ecific expression of a reporter gene in transgenic rice plants. In add
ition, two potential cis elements, Box I (nt -3 to +5) and Box II (nt
-53 to -39) were identified by DNA-protein interaction assays. In this
study, the results of further in vivo studies involving mutagenesis o
f selected DNA sequences and analysis of expression of a reporter gene
in transgenic rice plants revealed that, in addition to Box I and Box
II, other elements are required for phloem-specific gene expression,
among which are a direct repeat (ASL Box, nt -98 to -79) and a GATA mo
tif (nt -143 to -135). All the these elements bind rice nuclear factor
s specifically, and mutations of the elements were identified that res
ulted in loss-of-competition in electrophoretic mobility shift assays.
A DNA fragment comprising nt -164 to -32, which contains Box II, the
ASL Box and the GATA motif, conferred phloem-specific reporter gene ex
pression independent of Box when fused to a heterologous CaMV 35S mini
mal promoter and introduced to transgenic rice plants. Studies that in
troduced point mutations suggested that in the context of the -103 to
+45 promoter fragment, Box II and the ASL Box act synergistically to c
onfer tissue-specific gene expression. Similar studies in the -164 to
+45 promoter fragment indicated that the -164 to -103 region, which in
cludes the GATA motif, contains sequences that are functionally redund
ant with those in the -103 to -32 region, including the ASL Box and Bo
x II. It is concluded that these regions act additively to direct phlo
em-specific gene expression.