A chloroplast-localized mitochondrial calcium uniporter transduces osmotic stress in Arabidopsis (Nature Plants)

Calcium and chloroplasts are both at the heart of the signal transduction during environmental stress. Teardo et al. studied whether the chloroplast-localized mitochondrial calcium uniporter has a role in stress signaling. The group identified 6 homologs of mitochondrial calcium uniporter (MCU) in Arabidopsis, but only one (cMCU) was carrying a clear chloroplast localization signature. The cMCU localized to the outer chloroplast envelope in vivo where it mediated uptake of calcium ions. The mutants of cMCU showed extended calcium waves in response to osmotic stress and reduced calcium levels in the stroma. Interestingly, the effect of cMCU was detected only when plants were exposed to light, but not during the dark period. The mutants of cMCU had reduced stomatal aperture and were able to better maintain their photosynthetic efficiency during drought and recovery period. This resulted in increased tolerance to drought. Work by Teadro et al. shows how small changes in calcium signaling can result in significant alterations of environmental resilience. (Summarized by Magdalena Julkowska) Nature Plants 10.1038/s41477-019-0434-8