The Arabidopsis katamari2 Mutant Exhibits a Hypersensitive Seedling Arrest Response at the Phase Transition from Heterotrophic to Autotrophic Growth.

This article investigates the phenomenon of seedling growth arrest during the phase transition from heterotrophic to autotrophic growth in Arabidopsis thaliana, focusing on the membrane-trafficking mutant katamari2 (kam2). The study demonstrates that seedling arrest on sucrose-free solid medium is a reversible, adaptive stress response influenced by environmental factors such as the physical contact of shoots with the growth medium, rather than solely by carbon source deficiency. Experiments showed that increasing the gel concentration of the medium or covering it with perforated plastic sheets alleviated growth arrest in both kam2 mutants and wild-type plants, with transcriptomic analyses revealing gene expression changes related to hypoxia and defense responses preceding visible growth arrest. These findings suggest that seedling arrest is a general environmental stress response during seedling establishment and highlight the importance of growth conditions in studies of Arabidopsis mutants affecting membrane trafficking and phase transition.