Cell Type-Specific Imaging of Calcium Signaling inArabidopsis thalianaSeedling Roots Using GCaMP3

Cytoplasmic calcium ([Ca2+](cyt)) is a well-characterized second messenger in eukaryotic cells. An elevation in [Ca2+](cyt)levels is one of the earliest responses in plant cells after exposure to a range of environmental stimuli. Advances in understanding the role of [Ca2+](cyt)in plant development has been facilitated by the use of genetically-encoded reporters such as GCaMP. Most of these studies have relied on promoters such asCauliflower Mosaic Virus(35S) andUbiquitin10(UBQ10) to drive expression ofGCaMPin all cell/tissue types. Plant organs such as roots consist of various cell types that likely exhibit unique [Ca2+](cyt)responses to exogenous and endogenous signals. However, few studies have addressed this question. Here, we introduce a set ofArabidopsis thalianalines expressingGCaMP3in five root cell types including the columella, endodermis, cortex, epidermis, and trichoblasts. We found similarities and differences in the [Ca2+](cyt)signature among these root cell types when exposed to adenosine tri-phosphate (ATP), glutamate, aluminum, and salt, which are known to trigger [Ca2+](cyt)increases in root cells. These cell type-targeted GCaMP3 lines provide a new resource that should enable more in depth studies that address how a particular environmental stimulus is linked to specific root developmental pathways via [Ca2+](cyt).