b'The Presidents CommentaryUnderstanding Plant Cell GrowthAlthough it is well known that environmental signals, including light, determine the growth and shape of plant cells, the exact mechanisms for these cells response and reorganization has remained mysterious. To 12 better understand the process, Carnegies David Ehrhardt and team looked at the function of the protein kataninnamed for the Japanese sword, katanawhich responds to light perception by severing the intersections of microtubules within plant cells and triggering new growth. To understand how this process is stabilized in a growing plant, Ehrhardt and his team in Plant Biology studied the model plant Arabidopsis thaliana to understand the stabilizers at the point where severing occurs. After selectively deactivating candidate proteins by mutation and using time-lapse imaging to compare the mutants to normal plants, they found that the cytoplasmic linker associated protein (CLASP) works as a potent and specific stabilizer to promote regrowth after severing. These studies have important implications for understanding cellular function in both plants and animals.Arabidopsis thaliana is a member of the mustard family. Its fast life cycle of six weeks, ease of cultivation in small spaces, and large seed production make it ideal to use as a model organism to study genetics, cellular development, and more. Image courtesy Robin Kempster, Carnegie Institution for Science'