Cell Type-Specific Imaging of Calcium Signaling in Seedling Roots Using GCaMP3.

Cytoplasmic calcium ([Ca]) is a well-characterized second messenger in eukaryotic cells. An elevation in [Ca] levels is one of the earliest responses in plant cells after exposure to a range of environmental stimuli. Advances in understanding the role of [Ca] 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 as () and () to drive expression of in all cell/tissue types. Plant organs such as roots consist of various cell types that likely exhibit unique [Ca] responses to exogenous and endogenous signals. However, few studies have addressed this question. Here, we introduce a set of lines expressing in five root cell types including the columella, endodermis, cortex, epidermis, and trichoblasts. We found similarities and differences in the [Ca] signature among these root cell types when exposed to adenosine tri-phosphate (ATP), glutamate, aluminum, and salt, which are known to trigger [Ca] 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 [Ca].