Mitochondrial protease AtFtsH4 protects ageing Arabidopsis rosettes against oxidative damage under short-day photoperiod

Mitochondrial AtFtsH4 protease, whose catalytic site is exposed to the intermembrane space, is one of four inner membrane-bound FtsH proteases in Arabidopsis. We found that the loss of AtFtsH4 altered Arabidopsis leaf morphology at the late stage of rosette growth under short-day photoperiod, while such changes were not observed in ftsh4 mutants grown under long days. These morphological changes were correlated with elevated levels of both reactive oxygen species (ROS) and carbonylated proteins, which strongly suggested that ageing ftsh4 plants experienced oxidative stress. This view was supported by the accumulation of electron-dense material, presumably containing aggregated oxidized proteins, in mitochondria of ftsh4 plants with the most strongly malformed leaf blades. Taken together, our data published in the May issue of Plant Journal(1) suggest a link between the lack of AtFtsH4 protease, oxidative stress and altered leaf morphology at the late rosette stage under short days. Here, we present evidence that the onset of altered leaf morphology in ftsh4 correlates with an increase in the abundance of AtFtsH4 transcript observed in wildtype Arabidopsis growing under the same conditions. We also discuss how the lack of AtFtsH4 may cause oxidative stress towards the end of the vegetative growth in short days.