Targeted single-cell gene induction by optimizing the dually regulated CRE/loxP system by a newly defined heat-shock promoter and the steroid hormone in Arabidopsis thaliana

Infrared laser-induced gene expression in single cells characterized by quantitative imaging in Physcomitrium patens

A spatiotemporal understanding of gene function requires the precise control of gene expression in each cell. Here, we use an infrared laser-evoked gene operator (IR-LEGO) system to induce gene expression at the single-cell level in the moss Physcomitrium patens by heating a living cell with an IR laser and thereby activating the heat shock response. We identify the laser irradiation conditions that provide higher inducibility with lower invasiveness by changing the laser power and irradiation duration. Furthermore, we quantitatively characterize the induction profile of the heat shock response using a heat-induced fluorescence reporter system after the IR laser irradiation of single cells under different conditions. Our data indicate that IR laser irradiation with long duration leads to higher inducibility according to increase in the laser power but not vice versa, and that the higher laser power even without conferring apparent damage to the cells decelerates and/or delayed gene induction. We define the temporal shift in expression as a function of onset and duration according to laser power and irradiation duration. This study contributes to the versatile application of IR-LEGO in plants and improves our understanding of heat shock-induced gene expression.

Spatiotemporal control of transgene expression using an infrared laser in the crustacean Daphnia magna

The crustacean Daphnia magna is an emerging model for ecological and toxicological genomics. However, the lack of methods for spatial and temporal control of gene expression has impaired the elucidation of molecular mechanisms underlying responses to environments in vivo. Here we report local activation of the hsp70 promoter-driven gene cassette in D. magna by the infrared laser-evoked gene operator (IR-LEGO), a method for heating the target cells with infrared irradiation. We identified the heat-inducible promoter upstream of the D. magna hsp70-A gene. Using this promoter, we generated a transgenic Daphnia harboring the heat-shock responsive GFP reporter gene and confirmed that the GFP gene responds to heat treatment not only in juveniles and adults but also in embryos. We collected embryos from the reporter line and irradiated four different regions of interest in the embryos: a proximal region of the third thoracic segment, a part of the midline, a second maxilla, and a distal region of the endopodite of the second antenna, all of which increased GFP fluorescence with an infrared laser. Our results suggest that the IR-LEGO method is useful for spatial and temporal control of gene expression and would advance the functional genomics in D. magna.

Development of a tightly regulated copper-inducible transient gene expression system in Nicotiana benthamiana incorporating a suicide exon and Cre recombinase

Chemical-inducible gene expression systems are commonly used to regulate gene expression for functional genomics in various plant species. However, a convenient system that can tightly regulate transgene expression in Nicotiana benthamiana is still lacking. In this study, we developed a tightly regulated copper-inducible system that can control transgene expression and conduct cell death assays in N. benthamiana. We tested several chemical-inducible systems using Agrobacterium-mediated transient expression and found that the copper-inducible system exhibited the least concerns regarding leakiness in N. benthamiana. Although the copper-inducible system can control the expression of some tested reporters, it is not sufficiently tight to regulate certain tested hypersensitive cell death responses. Using the MoClo-based synthetic biology approach, we incorporated the suicide exon HyP5SM/OsL5 and Cre/LoxP as additional regulatory elements to enhance the tightness of the regulation. This new design allowed us to tightly control the hypersensitive cell death induced by several tested leucine-rich repeat-containing proteins and their matching avirulence factors, and it can be easily applied to regulate the expression of other transgenes in transient expression assays. Our findings offer new approaches for both fundamental and translational studies in plant functional genomics.