Cellulose synthase A genes (CesAs) are responsible for cellulose biosynthesis in plant cell walls. In this study, functions of secondary wall cellulose synthases PtrCesA4, PtrCesA7-A/B and PtrCesA8-A/B were characterized during wood formation in Populus trichocarpa (Torr. & Gray). CesA RNAi knockdown transgenic plants exhibited stunted growth, narrow leaves, early necrosis, reduced stature, collapsed vessels, thinner fiber cell walls and extended fiber lumen diameters. In the RNAi knockdown transgenics, stems exhibited reduced mechanical strength, with reduced modulus of rupture (MOR) and modulus of elasticity (MOE). The reduced mechanical strength may be due to thinner fiber cell walls. Vessels in the xylem of the transgenics were collapsed, indicating that water transport in xylem may be affected and thus causing early necrosis in leaves. A dramatic decrease in cellulose content was observed in the RNAi knockdown transgenics. Compared with wildtype, the cellulose content was significantly decreased in the PtrCesA4, PtrCesA7 and PtrCesA8 RNAi knockdown transgenics. As a result, lignin and xylem contents were proportionally increased. The wood composition changes were confirmed by solid-state NMR, two-dimensional solution-state NMR and sum-frequency-generation vibration (SFG) analyses. Both solid-state nuclear magnetic resonance (NMR) and SFG analyses demonstrated that knockdown of PtrCesAs did not affect cellulose crystallinity index. Our results provided the evidence for the involvement of PtrCesA4, PtrCesA7-A/B and PtrCesA8-A/B in secondary cell wall formation in wood and demonstrated the pleiotropic effects of their perturbations on wood formation.

中文翻译：

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CesA4，CesA7-A / B和CesA8-A / B参与毛果杨木材次生壁的形成。

纤维素合酶A基因（CesAs）负责植物细胞壁中纤维素的生物合成。在这项研究中，次生壁纤维素合成酶PtrCesA4，PtrCesA7-A / B和PtrCesA8-A / B的功能在毛果杨木材形成过程中得到了表征（Torr。和Gray）。CesA RNAi基因敲低的转基因植物表现出发育不良，叶片狭窄，早期坏死，身材矮小，血管萎缩，纤维细胞壁变薄和纤维管腔直径增大。在RNAi基因敲低转基因中，茎表现出降低的机械强度，同时降低了断裂模量（MOR）和弹性模量（MOE）。机械强度降低可能是由于纤维孔壁更薄所致。转基因木质部中的血管塌陷，表明木质部中的水运输可能受到影响，从而导致叶片早期坏死。在RNAi敲低的转基因中观察到纤维素含量的显着降低。与野生型相比，PtrCesA4，PtrCesA7和PtrCesA8 RNAi基因敲低转基因中的纤维素含量显着降低。结果，木质素和木质部含量成比例增加。通过固态NMR，二维固溶态NMR和和频产生振动（SFG）分析确认木材组成的变化。固态核磁共振（NMR）和SFG分析均表明PtrCesAs的敲低不影响纤维素的结晶度指数。我们的结果为PtrCesA4，PtrCesA7-A / B和PtrCesA8-A / B参与木材的次生细胞壁形成提供了证据，并证明了其扰动对木材形成的多效性作用。