Katanin复合体调节亚基KTN80调控根形态建成的作用机制

The Katanin regulatory subunit KTN80 regulates root morphogenesis

摘要:

Katanin复合体是迄今在植物中发现的唯一具有微管切割功能的蛋白复合体，在植物细胞形态重塑与生长发育过程中发挥关键作用。该复合体由催化亚基KTN1和调节亚基KTN80组成。在拟南芥中，KTN80存在4个同源基因，但其功能尚未明确。为深入探究KTN80在植物根形态建成中的作用机制，本研究对KTN80s (KTN80.1、KTN80.2、KTN80.3和KTN80.4)进行β-d-葡萄糖苷酸酶(β-glucuronidase, GUS)组织染色分析，发现它们在根组织中均显著表达，但其表达模式存在差异。进一步表型分析表明，ktn80.1234根发育异常，其主根短而粗，但根毛长度却显著长于野生型。显微结构观察发现，ktn80.1234根分生区和伸长区均显著缩短，细胞体积增大，呈现各向同性扩展特征。此外，利用活细胞成像技术观察根细胞周质微管动态，发现ktn80.1234微管排列紊乱，阻碍了细胞的正常快速伸长。对根分生区有丝分裂细胞的微管阵列进一步观察表明，ktn80.1234细胞中早前期带(preprophase band, PPB)微管阵列出现异常，部分成膜体微管也出现不正常的倾斜排列。综上，KTN80通过精确调控细胞微管骨架阵列的重塑，进而调控根的形态建成。本研究为深入理解Katanin复合体在植物生长发育中的作用机制提供了新的见解。

Abstract:

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.