enumerate genetically encoded fluorescent biosensors that have
been used for the past two decades in plant science, and how they
must be used.
1.1 Types of
Genetically Encoded
Fluorescent
Biosensors
1.1.1 Fluorescent
Proteins
Fluorescent proteins (FPs), such as variants of Aequorea victoria
Green Fluorescent Protein (AvGFP) [1] and Discosoma Red Fluorescent Protein (DsRed) [2], consist of 11 β-sheets forming a
β-barrel structure in which a chromophore is located [3]. FPs
have been developed and utilized for minimally invasive in vivo
imaging.
1.1.2 Indirect
Fluorescent Biosensors
Phytohormones and nutrients regulate many genes through regulation of RNA transcription and degradation. Such processes can be
monitored with the help of fluorescent biosensors. The simplest
sensors are transcriptional reporters. A well-known example is the
auxin response reporter, which uses the DR5 promoter driving a
reporter protein. It consists of a minimal promoter fused to extra
copies of TGTCTC/GAGACA repeats (the auxin-response element, AuxRE) [4] followed by a reporter gene for either a FP or
β-glucuronidase (GUS). The DR5 reporter system has advantages,
such as monitoring slow processes, but also disadvantages, such as
the time lag between transcription and maturation of the reporter,
which decreases its temporal resolution. To overcome the drawbacks of the DR5 reporter, Brunoud et al. engineered an auxin
Table 1
(continued)
Target/analyte
Biosensor
Sensor type
Ref.
ABA
ABACUS
FRET-based sensor
[28]
ABAleon
[29]
GA
GPS1
FRET-based sensor
[30]
GFP-RGA
Degron-based sensor
[6, 7]
Jasmonic acid
Jas9-Venus
Degron-based sensor
[8]
Strigolactone
StrigoQuant
Degron-based sensor
[9]
Ca
2+
GCaMP3
Single FP extrinsic
[44–48]
R-GECO1
[50]
R-GECO1-mTurquoise
Dual FP extrinsic
[59]
MatryoshCaMP6s
[60]
YC2.1
FRET-based sensor
[14, 15]
B(OH) 3
uNIP5;1-Venus
Translational sensor
[12]
Pi
cpFLIPPi
FRET-based sensor
[16]
Zn
2+
eCALWY
FRET-based sensor
[18]
The Use of Genetically Encoded Fluorescent Biosensors
305
been used for the past two decades in plant science, and how they
must be used.
1.1 Types of
Genetically Encoded
Fluorescent
Biosensors
1.1.1 Fluorescent
Proteins
Fluorescent proteins (FPs), such as variants of Aequorea victoria
Green Fluorescent Protein (AvGFP) [1] and Discosoma Red Fluorescent Protein (DsRed) [2], consist of 11 β-sheets forming a
β-barrel structure in which a chromophore is located [3]. FPs
have been developed and utilized for minimally invasive in vivo
imaging.
1.1.2 Indirect
Fluorescent Biosensors
Phytohormones and nutrients regulate many genes through regulation of RNA transcription and degradation. Such processes can be
monitored with the help of fluorescent biosensors. The simplest
sensors are transcriptional reporters. A well-known example is the
auxin response reporter, which uses the DR5 promoter driving a
reporter protein. It consists of a minimal promoter fused to extra
copies of TGTCTC/GAGACA repeats (the auxin-response element, AuxRE) [4] followed by a reporter gene for either a FP or
β-glucuronidase (GUS). The DR5 reporter system has advantages,
such as monitoring slow processes, but also disadvantages, such as
the time lag between transcription and maturation of the reporter,
which decreases its temporal resolution. To overcome the drawbacks of the DR5 reporter, Brunoud et al. engineered an auxin
Table 1
(continued)
Target/analyte
Biosensor
Sensor type
Ref.
ABA
ABACUS
FRET-based sensor
[28]
ABAleon
[29]
GA
GPS1
FRET-based sensor
[30]
GFP-RGA
Degron-based sensor
[6, 7]
Jasmonic acid
Jas9-Venus
Degron-based sensor
[8]
Strigolactone
StrigoQuant
Degron-based sensor
[9]
Ca
2+
GCaMP3
Single FP extrinsic
[44–48]
R-GECO1
[50]
R-GECO1-mTurquoise
Dual FP extrinsic
[59]
MatryoshCaMP6s
[60]
YC2.1
FRET-based sensor
[14, 15]
B(OH) 3
uNIP5;1-Venus
Translational sensor
[12]
Pi
cpFLIPPi
FRET-based sensor
[16]
Zn
2+
eCALWY
FRET-based sensor
[18]
The Use of Genetically Encoded Fluorescent Biosensors
305