Biosensors: A Sneak Peek into Plant Cell’s Immunity

Biosensors are indispensable tools to follow plant’s immunity as its spatiotemporal dimension is key in withstanding the complex plant immune signaling. The diversity of genetically encoded biosensors in plants is expanding, covering new analytes with ever higher sensitivity and robustness, but their assortment is limited in some aspects, such as their use to follow biotic stress response, employing more than one biosensor in the same chassis and their implementation into crops. In this review, we focused on the available biosensors that encompass these aspects. We show that in vivo imaging of calcium and reactive oxygen species is satisfactorily covered with the available genetically encoded biosensors, while on the other hand they are still underrepresented when it comes to imaging of the main three hormonal players of the immune response, salicylic acid, ethylene and jasmonic acid. Following more than one analyte in the same chassis, upon one or more conditions has so far been possible by using the most advanced genetically encoded biosensors in plants which allow to monitor calcium and two main hormonal pathways involved in plant development, auxin and cytokinin. These kinds of biosensors are also the most evolved in crops. In the last section, we gathered the challenges in the use of the biosensors and showed some strategies to overcome them.