What Drives Symbiotic Calcium Signalling In Legumes? Insights And Challenges Of Imaging

Abstract

We review the contribution of bioimaging in building a coherent understanding of Ca 2+ signalling during legume-bacteria symbiosis. Currently, two different calcium signals are believed to control key steps of the symbiosis: a Ca 2+ gradient at the tip of the legume root hair is involved in the development of an infection thread, while nuclear Ca 2+ oscillations, the hallmark signal of this symbiosis, controls the formation of the root nodule, where bacteria fix nitrogen. Additionally, different Ca 2+ spiking signatures have been associated with specific infection stages. Bioimaging is intrinsically a cross-disciplinary area that requires integration of image recording, processing and analysis. We use experimental examples to critically evaluate previously established conclusions and draw attention to challenges caused by the varying nature of the signal-to-noise ratio in live imaging. We hypothesise that nuclear Ca 2+ spiking is a wide-range signal involving the entire root hair, and that Ca 2+ signature may be related to cytoplasmic streaming.

Encoding, transmission, decoding, and specificity of calcium signals in plants

“…These developments are delivering new insights and quantification at increasing spatio-temporal resolution with multiple sensors simultaneously. Some related challenges in relation to interpreting calcium images have been described ( Vaz Martins and Livina, 2019 ). Excellent reviews on the latest imaging advances have recently been published ( Clark et al , 2020 ; Grenzi et al , 2021 ; Rowe and Jones, 2021 ; Sadoine et al , 2021 ).…”