Perturbation of Wood Cellulose Synthesis Causes Pleiotropic Effects in Transgenic Aspen

Abstract

Genetic manipulation of cellulose biosynthesis in trees may provide novel insights into the growth and development of trees. To explore this possibility, the overexpression of an aspen secondary wall-associated cellulose synthase (PtdCesA8) gene was attempted in transgenic aspen (Populus tremuloides L.) and unexpectedly resulted in silencing of the transgene as well as its endogenous counterparts. The main axis of the transgenic aspen plants quickly stopped growing, and weak branches adopted a weeping growth habit. Furthermore, transgenic plants initially developed smaller leaves and a less extensive root system. Secondary xylem (wood) of transgenic aspen plants contained as little as 10% cellulose normalized to dry weight compared to 41% cellulose typically found in normal aspen wood. This massive reduction in cellulose was accompanied by proportional increases in lignin (35%) and non-cellulosic polysaccharides (55%) compared to the 22% lignin and 36% non-cellulosic polysaccharides in control plants. The transgenic stems produced typical collapsed or 'irregular' xylem vessels that had altered secondary wall morphology and contained greatly reduced amounts of crystalline cellulose. These results demonstrate the fundamental role of secondary wall cellulose within the secondary xylem in maintaining the strength and structural integrity required to establish the vertical growth habit in trees.

Powerful regulatory systems and post-transcriptional gene silencing resist increases in cellulose content in cell walls of barley

“…A similar phenotype has been described in Arabidopsis irx mutants [32]. When Joshi and collaborators [33] introduced another copy of the SCW Populus tremuloides L cellulose synthase PtdCesA8 gene, which is the putative orthologue of barley HvCesA7 , driven by the CaMV 35S promoter into transgenic poplar plants, severe silencing of both the endogenous and transgene CesAs , together with a dramatically reduced cellulose content, dwarfism and a collapsed xylem phenotype, were observed. However, Joshi et al [33] did not report a reduction in wall thickness.…”

Engineering of plant cell walls for enhanced biofuel production

“…De novo and homology modeling of the catalytic domain of a cotton cellulose synthase shows good agreement with the bacterial one [60 ] indicating that the cellulose synthesis is processive and that cellulose synthesis does not require a primer unlike previously thought [61]. Overexpression of CesAs in poplar did not lead to the desired accumulation of cellulose, but instead resulted in a reduction in wall cellulose due to silencing of endogenous CesAs [62]. The plants showed severe, aberrant, pleiotropic phenotypes implying that manipulating the expression levels of CesAs might not be a fruitful approach.…”

Advances in Genetic Manipulation of Lignocellulose to Reduce Biomass Recalcitrance and Enhance Biofuel Production in Bioenergy Crops

“…For cellulose biosynthesis, first CesA compounds gathered into Golgi apparatus and then transmitted to the plasma membrane in three stage: initiation, elongation, and termination [70] In secondary cell walls, the presence of CesA 4 , CesA 7 , and CesA 8 is needed [71], while in PCWs the interaction of CesA 1 , CesA 3 , and CesA 6 (or CesA 1 , CesA 3 , and CesA 6 -releated proteins) is required [68]. In numerous plant species, the CesA families have been distinguished, comprising Arabidopsis [72], rice [73,74], wheat [75], barley [76], maize [77], poplar [78], cotton [79]. Through various genetic approaches numerous specific CesA mutants have been distinguished, which most mutants present reduced cellulose levels and imperfect plant growth ( Table 2).…”

“…For the biosynthesis of monolignols there are two main steps, in the first stage more than ten genes are engaged which are including: cinnamate 4-hydroxylase (C4H) [96], 4-coumarate-CoA ligase (4CL) [58], coumarate 3-hydroxylase (C3H) [97], cinnamoyl-CoA reductase (CCR) [98], cinnamyl alcohol dehydrogenase (CAD) [99], ferulate 5-hydroxylase (F5H) [100], and 5-hydroxyferulic acid Omethyltransferase (caffeic acid/COMT) [101], caffeoyl-CoA 3-Omethyltransferase (CCoAOMT) [79], phenylalanine ammonia lyase (PAL) [102], shikimate hydroxycinnamoyl transferase (HCT) [103]. In the second steps, catalyze hydroxylation and methylation reactions then synthesize lignin monomers [104].…”