Involvement of CesA4, CesA7-A/B and CesA8-A/B in secondary wall formation in Populus trichocarpa wood

Abstract

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.

Functional understanding of secondary cell wall cellulose synthases in Populustrichocarpa via the Cas9/gRNA‐induced gene knockouts

“…A recent study reported similar and moderate defects in PtrCesA RNAi transgenic plants in P . trichocarpa (Abbas et␣al ., 2020 ). Serious defects of these null mutants exhibited prostrate growth, loss of apical dominance and significant reductions in stem diameters, internode lengths and leaf sizes (Figs 3 , S6, S7 ).…”

“…trichocarpa (Abbas et al, 2020). Serious defects of these null mutants exhibited prostrate growth, loss of apical dominance and significant reductions in stem diameters, internode lengths, and leaf sizes (Figs.…”

Direct fluorescence imaging of lignocellulosic and suberized cell walls in roots and stems

“…Anatomical investigations of cell wall structure play essential roles in disciplines such as plant ecophysiology, taxonomy, plant development and plant biomechanics ( Carlquist 2001 ; Hacke et al 2006 ; Rossi et al 2012 ; Beeckman 2016 ; Deslauriers et al 2016 ; Özparpucu et al 2017 ; Begum et al 2018 ). In modern studies, the formation and characterization of lignocellulosic or suberized cells are frequently targeted ( Abe et al 1997 ; Chaffey 2002 ; Chaffey et al 2002 ; Salmén and Burgert 2009 ; Yamagishi et al 2012 ; Pesquet et al 2013 ; Tobimatsu et al 2013 ; Kudo et al 2014 , 2018 ; Daniel 2016 ; Chabbert et al 2018 ; Abbas et al 2019 ). However, often the applied protocols for plant sample preparation are decades old and appear to be trailing the rapid progress in light microscopy equipment.…”

Tailoring renewable materials via plant biotechnology

“…However, modifications of CesA genes in trees have not shown similar positive impacts on reducing cellulose crystallinity. In poplar, PtrCesA4 , PtrCesA7-A/B and PtrCesA8-A/B genes were characterized as the cellulose synthases responsible for the synthesis of secondary cell wall cellulose [ 173 ], and RNAi-suppression of these genes exhibited significant decreases in cellulose content, reductions in growth, collapsed vessels, and thinner fibre cell walls, without changes in the CrI [ 173 ].…”