Biology Reference
In-Depth Information
Sequential deletion analysis of the
Nec1
promoter revealed that there are
multiple regulatory elements within the promoter. One of these elements,
which contains a
MYB
binding site, is responsible for the temporal pattern of
Nec1
expression. The other element, which is upstream from the temporal
element, is apparently involved in tissue specificity of
Nec1
expression.
When this element is in place, the
Nec1
promoter shows tight nectary-
specific expression. When this element is deleted, however, the
Nec1
pro-
moter suddenly gains activity in the floral petals. We have interpreted these
analyses to mean that this second element contains a binding site for a petal-
expressed repressor protein that normally functions in the flower to limit ex-
pression of the
Nec1
promoter to the nectaries (Carter & Thornburg, 2003).
It is not clear whether the
Nec1
promoter contains additional elements that
are important in
Nec1
expression or whether there are additional tissue-
specific repressor proteins that further control
Nec1
expression by limiting
the expression of this promoter.
6
NECTARY MOLECULAR BIOLOGY IN OTHER
SPECIES
In addition to the nectar-specific proteins (
nectarins
; see Nicolson & Thorn-
burg 2007, Chapter 5 in this volume), there are a number of other nectary-
specific genes that have been identified from various species. Leek (
Allium
porrum
) has been shown to express two nectarins, a 50 kDa alliinase and a
13 kDa mannose-specific lectin (Peumans et al., 1997). Both of these proteins
have defence-related functions (see Nicolson & Thornburg 2007, Chapter 5
in this volume) and probably serve to maintain nectar in an axenic state,
much as does the nectar redox cycle.
6.1
Other nectary-expressed genes
A list of genes known to be specifically expressed in plant nectaries is pre-
sented in Table 5. These genes correspond to a diverse group of proteins that
include defence-related proteins, transcription factors, signal transduction
factors, and biosynthetic enzymes. Most of these proteins are not specific,
but are also expressed in other plant organs. ESTs encoding many of these
genes have been identified among our EST studies, thereby confirming that
these genes are indeed nectary-expressed.
Important exceptions from Table 5 include the
CRABS CLAW
(
CRC
) tran-
scription factor from
Arabidopsis thaliana
(discussed in “Origin of the floral
