ROS inhibits microtubule dynamics and cell growth heterogeneity during Arabidopsis sepal morphogenesis

Developing organs grow to reproducible sizes and shapes, yet the growth of their constituent cells can be highly heterogeneous and fluctuating. During wild-type Arabidopsis thaliana sepal development, fluctuations in cell growth average because the fluctuations are not strongly correlated spatially or temporally, and so the sepals grow to uniform sizes and shapes. In contrast, the sepals of the ftsh4-5 mutant develop to variable sizes and shapes. F ts H4 encodes a mitochondrial i-AAA protease. Reactive oxygen species (ROS) accumulate in ftsh4-5 mutants, and lowering ROS levels rescues the sepal size and shape variability. Here, we find that elevated ROS promotes correlated growth fluctuations and causes cortical microtubules to become more "crisscrossed" and stable. The growth rates of the cells with crisscrossed microtubules are lower and more correlated in time, which impairs spatiotemporal averaging of growth. This suggests that ROS affects microtubule dynamics and cell growth fluctuations, which are necessary for robust morphogenesis.