Agriculture Reference
In-Depth Information
The gene fusion concept could be used to measure complex phenomena, even in
the absence of mechanistic knowledge of how that phenomenon works (Jefferson
1993
). This technology is completely general and could be exploited to develop
transgenic bioindicators providing signals whose intensity is proportional to the
concentration of a given analyte in growing environment (i.e. mineral nutrients,
pollutants, water, etc.) or to the intensity of a biotic or abiotic stress that plants
could experience during their growth. Potential targeted traits to be monitored are
only limited by the availability of specific promoters (or controllers) driving the
reporter expression under a specific condition.
Recently these technologies have been applied in plants to develop model
transgenic bioindicators of the nutritional status to be used for laboratory purposes.
To date, reporter gene activity has been used to assess the phosphate, sulfate and
magnesium status in
Arabidopsis
and also to detect the level of nickel in the
growing medium (Hammond et al.
2003
; Krizek et al.
2003
; Maruyama-Nakashita
et al.
2006
; Kamiya et al.
2012
). In all these studies GUS, GFP and LUC have been
successfully used as reporter genes to indicate nutritional status under the control of
promoter sequences indirectly identified by microarray analyses.
Hammond and co-workers (
2003
) first proposed the creation of an
Arabidopsis
transgenic bioindicator, able to monitor plant phosphorous status. They fused GUS
with the promoter of the phosphate starvation responsive gene
SQD1
(a gene
involved in the synthesis of sulfolipids), obtaining an
Arabidopsis
transgenic line
in which GUS activity increased following P starvation. Interestingly, the reporter
responses to P withdrawal were much more rapid and quantitative than phenotypic
observations, showing this approach is particularly suitable for developing efficient
systems for monitoring plant P status. More recently Kamiya et al. (
2012
) used a
similar approach to establish a novel monitoring system for magnesium in plants. In
particular they obtained an
Arabidopsis
transgenic line that expressed luciferase
(LUC) under the control of the Mg deficiency-inducible
CAX3
promoter. The
transgenic lines showed a clear response under low Mg conditions and the degree
of luminescence reflected the accumulation of endogenous
CAX3
mRNA. How-
ever,
CAX3
induction does not seem to be specific to low Mg, since the levels of
other ions (Ca
2+
and Na
+
) or P starvation may influence transcription (Shigaki and
Hirschi
2000
).
Notwithstanding some limitations
Arabidopsis
plants could also be used
as tools in basic research aimed at isolating novel mutants disrupted in nutrient
homeostasis or identifying plants with enhanced nutrient use efficiency. For
instance, the key transcription factor, SLIM1, regulating the sulfur assimilatory
pathway has recently been identified by screening
Arabidopsis
mutants carrying a
fluorescent reporter gene under the control of the sulfur limitation-responsive
promoter of the SULTR1;2 sulfate transporter (Maruyama-Nakashita et al.
2006
).
Using this approach it is possible to identify all the potential genes involved in
controlling the expression of SULTR1;2 under sulfur shortage, since in this condi-
tion the relative mutants will display altered fluorescence emissions as compared to
the wild type bioindicator.
smart
'
'
