[The Katanin regulatory subunit KTN80 regulates root morphogenesis]

The Katanin complex is the only protein complex identified in plants to date that possesses microtubule-severing activity, playing a pivotal role in cell shape remodeling and growth. This complex consists of a catalytic subunit KTN1 and a regulatory subunit KTN80. In Arabidopsis thaliana, KTN80 is encoded by four homologous genes, though their specific functions remain unclear. To elucidate the role of KTN80 in root morphogenesis, we performed a detailed expression analysis of KTN80s (KTN80.1, KTN80.2, KTN80.3, and KTN80.4) via β-glucuronidase histochemical staining. Our findings confirmed that all the four genes were actively expressed in roots, yet they exhibited distinct spatial expression patterns. The phenotypic analysis showed that the ktn80.1234 mutant exhibited abnormal root development, characterized by shortened and robust primary root but significantly extended root hairs compared to the wild type. Microscopic examination showed marked reductions in both the meristematic zone length and the elongation zone length, accompanied by enlarged cells exhibiting isotropic expansion in the mutant. To probe the underlying cellular cause, we employed live-cell imaging to observe cortical microtubule dynamics and discovered disorganized microtubule arrays in the mutant, which impeded normal, rapid cell elongation. Further investigation of the root meristem showed that in ktn80.1234 cells, both the preprophase band (PPB) and the phragmoplast had abnormal microtubule arrays. The PPB microtubules were disorganized, while some phragmoplast microtubules displayed abnormal oblique arrangements. In conclusion, our results demonstrate that KTN80 is essential for root morphogenesis by precisely regulating the reorganization of the cellular microtubule cytoskeleton. This study provides new insights for understanding the role of the Katanin complex in plant growth and development.