Resolving phytohormone response zones by fluorescent reporters

Phytohormones such salicylic acid (SA), ethylene (ET), and jasmonic acid (JA) are known to regulate plant immunity, but their spatial dynamics has remained unclear. Using a set of fluorescent reporters in Arabidopsis, Calabria et al. resolved the hormonal responses upon Fusarium oxysporum infection at single-cell level. The authors selected 75 immunity-related genes and used their promoters to drive fluorescent protein expressions in Arabidopsis. The promoters of phytohormone-biosynthesis genes reported upregulated SA and ET syntheses in cells bordering the fungal-colonized zone. Furthermore, the damage-associated molecular pattern (DAMP) signal and reactive oxygen species (ROS) reporters showed signal maxima in the cells where SA and ET syntheses peaked. The overlapping signal maxima explain the hypersensitive response (HR) close to the fungal-colonised zone. While the HR zone acted as the first line of defence, JA was synthesized in the succeeding area which is known as the second line of defence. The reporters were demonstrated useful to delineate hormonal responses at single-cell level. The authors donated the 75 reporter plasmids to AddGene for distribution. They will be useful for other stress studies in plants. (Summary by Yee-Shan Ku @YeeShanKu1) Journal of Experimental Botany 10.1093/jxb/erae516