Department of Botany, University of British Columbia, Vancouver, BC V6T 1Z4, Canada.
Department of Wood Science, University of British Columbia, Vancouver, BC V6T 1Z4, Canada.
Proc Natl Acad Sci U S A. 2018 Jul 3;115(27):E6366-E6374. doi: 10.1073/pnas.1802113115. Epub 2018 Jun 5.
In plants, plasma membrane-embedded CELLULOSE SYNTHASE (CESA) enzyme complexes deposit cellulose polymers into the developing cell wall. Cellulose synthesis requires two different sets of CESA complexes that are active during cell expansion and secondary cell wall thickening, respectively. Hence, developing xylem cells, which first undergo cell expansion and subsequently deposit thick secondary walls, need to completely reorganize their CESA complexes from primary wall- to secondary wall-specific CESAs. Using live-cell imaging, we analyzed the principles underlying this remodeling. At the onset of secondary wall synthesis, the primary wall CESAs ceased to be delivered to the plasma membrane and were gradually removed from both the plasma membrane and the Golgi. For a brief transition period, both primary wall- and secondary wall-specific CESAs coexisted in banded domains of the plasma membrane where secondary wall synthesis is concentrated. During this transition, primary and secondary wall CESAs displayed discrete dynamic behaviors and sensitivities to the inhibitor isoxaben. As secondary wall-specific CESAs were delivered and inserted into the plasma membrane, the primary wall CESAs became concentrated in prevacuolar compartments and lytic vacuoles. This adjustment in localization between the two CESAs was accompanied by concurrent decreased primary wall CESA and increased secondary wall CESA protein abundance. Our data reveal distinct and dynamic subcellular trafficking patterns that underpin the remodeling of the cellulose biosynthetic machinery, resulting in the removal and degradation of the primary wall CESA complex with concurrent production and recycling of the secondary wall CESAs.
在植物中，质膜嵌入的纤维素合酶（CESA）酶复合物将纤维素聚合物沉积到正在发育的细胞壁中。纤维素合成需要两套不同的 CESA 复合物，它们分别在细胞扩张和次生细胞壁增厚过程中发挥作用。因此，首先经历细胞扩张随后沉积厚次生壁的发育木质部细胞需要将其 CESA 复合物从初生壁特异性 CESAs 完全重组成次生壁特异性 CESAs。我们通过活细胞成像分析了这种重塑的原理。在次生壁合成开始时，初生壁 CESAs 停止被递送到质膜，并逐渐从质膜和高尔基体中被移除。在短暂的过渡时期，初生壁和次生壁特异性 CESAs 共存于质膜的带状区域，次生壁合成集中于此。在这个过渡期间，初生壁和次生壁 CESAs 表现出不同的动态行为和对抑制剂异羟肟酸的敏感性。随着次生壁特异性 CESAs 的递送到质膜并插入其中，初生壁 CESAs 集中在液泡前区和溶酶体中。这两种 CESAs 在定位上的调整伴随着初生壁 CESA 的含量减少和次生壁 CESA 的含量增加。我们的数据揭示了不同的和动态的细胞内运输模式，这些模式为纤维素生物合成机器的重塑提供了基础，导致初生壁 CESA 复合物的去除和降解，同时产生和循环利用次生壁 CESAs。
