Research
Plant cells lack structurally defined microtubule organizing center (MTOC) like the centrosomes. It is intriguing how plant cells organize acentrosomal microtubule (MT) arrays. Plant cells establish the interphase MT array, known as cortical MTs, in a two-dimension form underneath the plasma-membrane to orient the deposition of cellulose microfibrils during cellulose biosynthesis. Plant cortical MTs undergo highly dynamic reorganization in response to the developmental cues or biotic/abiotic stresses. However, the mechanism underlying the dynamicity of plant cortical MTs remains largely unknown.
Prof. KONG Zhaosheng’s group at the Institute of Microbiology of Chinese Academy of Sciences discovered that augmin triggers MT-dependent MT nucleation in interphase plant cells. They revealed that the augmin complex was docked to cortical MTs and then recruited the g-tubulin ring complex (g-TuRC) on site to initiate a nucleation event either in the branching form or in the parallel form.
The researchers generated augmin knockdown lines by expressing an artificial microRNA, amiR-AUG6. The amiR-AUG6 cells displayed highly parallel and bundled MTs, replacing the fine and mesh-like MT network in the wild-type cells. They found that when the function of the augmin complex was compromised, MT nucleation frequency was drastically reduced, most obviously for the branching nucleation, and the average nucleation angle was also reduced.
It is well-accepted that the augmin complex plays a critical role in mitotic spindle assembly by nucleating short and dense intraspindle MTs in both animal and plant cells. However, it still lacks in vivo evidence that links MT nucleation with augmin’s dynamic behavior. Their findings afford insights into this field, and further extend their understanding of mitotic-specific function of augmin to the crucial regulatory function in the assembly of interphase MTs. The results suggested that augmin functions as an adaptor to regulate the geometry of MT nucleation.
The work was supported by the National Science Foundation of China. The results were published in Current Biology.
Contact:
Prof. KONG Zhaosheng
E-mail: zskong@im.ac.cn
