The TWD40-2 protein and the AP2 complex cooperate in the clathrin-mediated endocytosis of cellulose synthase to regulate cellulose biosynthesis
Friday, 2015/10/16 | 07:04:18
|
Logan Bashline, Shundai Li, Xiaoyu Zhu, and Ying Gu Significance
Our study advances the understanding of how plants make cellulose, a critical constituent of the plant cell wall and the most abundant organic polymer in the terrestrial biosphere. Cellulose is synthesized at the plasma membrane by cellulose synthase (CESA) complexes. Here we highlight the importance of regulated CESA endocytosis in cellulose biosynthesis in Arabidopsis. Furthermore, we show that the TWD40-2 protein, a putative member of the TPLATE complex, functions in clathrin-mediated endocytosis (CME) in ways that are both distinct from and cooperative with the functionally conserved CME adaptor protein 2 (AP2) complex. Because the TPLATE complex of plants is not conserved in animals, our characterization of TWD40-2 offers the opportunity to provide insight into the evolution of eukaryotic trafficking machinery. Abstract
Cellulose biosynthesis is performed exclusively by plasma membrane-localized cellulose synthases (CESAs). Therefore, the trafficking of CESAs to and from the plasma membrane is an important mechanism for regulating cellulose biosynthesis. CESAs were recently identified as cargo proteins of the classic adaptor protein 2 (AP2) complex of the clathrin-mediated endocytosis (CME) pathway. The AP2 complex of the CME pathway is conserved in yeast, animals, and plants, and has been well-characterized in many systems. In contrast, the recently discovered TPLATE complex (TPC), which is proposed to function as a CME adaptor complex, is only conserved in plants and a few other eukaryotes. In this study, we discovered that the TWD40-2 protein, a putative member of the TPC, is also important for the endocytosis of CESAs. Genetic analysis between TWD40-2 and AP2M of the AP2 complex revealed that the roles of TWD40-2 in CME are both distinct from and cooperative with the AP2 complex. Loss of efficient CME in twd40-2-3 resulted in the unregulated overaccumulation of CESAs at the plasma membrane. In seedlings of twd40-2-3 and other CME-deficient mutants, a direct correlation was revealed between endocytic deficiency and cellulose content deficiency, highlighting the importance of controlled CESA endocytosis in regulating cellulose biosynthesis.
See: http://www.pnas.org/content/112/41/12870.abstract.html?etoc PNAS October 13, 2015; vol. 112 no. 41: 12870–12875
Fig. 1. twd40-2-3 is a knockdown allele that exhibits dwarf phenotypes and shows a genetic interaction with ap2m-1. (A and B) The length of etiolated seedlings and light-grown seedling roots was measured. (Scale bars, 10 mm.) Error bars are SEM. ***P < 0.0001 (10 ≤ n ≤ 13 for each genotype). (C and D) Col-0, ap2m-1, twd40-2-3, and ap2m-1 twd40-2-3 plants are shown at 3 and 6 wk old. Thirty-three percent of ap2m-1 twd40-2-3 mutants died at 3 wk. [Scale bars, 1 cm (C) and 5 cm (D).] (E) Western blot analysis of TWD40-2 expression in total protein extracts from Col-0, ap2m-1, twd40-2-3, ap2m-1 twd40-2-3, AP2M-YFP ap2m-1, and GFP-TWD40-2 twd40-2-3 seedlings. TWD40-2 protein levels are reduced in seedlings harboring twd40-2-3. GFP-TWD40-2 twd40-2-3 shows both knocked-down endogenous TWD40-2 and mobility-shifted GFP-TWD40-2. The loading control is a Coomassie gel. |
![]() ![]() ![]() |
[ Other News ]___________________________________________________
|