Abstract
Increasing the wood density to a preferred range contributes to upgrading the value of wood as raw material. Lignin manipulation can also improve wood quality. This study attempted to accelerate secondary cell wall formation in transgenic poplar with an altered lignin structure. To achieve this, OsSWN1, a rice master switch for secondary cell wall formation in fiber cells, was overexpressed in poplar plants in which monolignol biosynthesis was suppressed by the expression of an RNA-interference construct targeted to the gene for cinnamyl alcohol dehydrogenase 1. The generated transgenic poplars successfully overexpressed the chimeric OsSWN1 construct and monolignol biosynthesis remained altered in these plants. Secondary cell wall thickness was increased in the transgenic plants and their wood density was higher compared to the background line. No difference in lignin content was observed, except in one transgenic line. High saccharification characteristics observed in the background line were preserved in the transgenic line with lower OsSWN1 overexpression, but higher OsSWN1 overexpression had a slight negative impact on enzyme saccharification. Our data suggested that fine-tuning of accelerated deposition of the secondary cell wall combined with alteration of monolignol biosynthesis should improve the lignocellulose quality for conventional and future biorefinery uses.
Highlights
Lignin is a major chemical component of cell walls in terrestrial plant biomasses
Poplar transformation A chimeric Rice secondary wall NAC domain protein 1 (OsSWN1) construct under the control of the Arabidopsis NAC secondary wall thickening promoting factor 3 (NST3) promoter [16] was introduced into hpCAD19 transgenic poplar line (Populus tremula x Populus alba clone INRA 717-1B4) [11] in which CAD1 activity was suppressed by the cauliflower mosaic virus 35S promoter-driven hairpin RNAi strategy
Transgenic poplar generation and OsSWN1 expression The tissue-preferential pattern of NST3 expression met our objective, i.e., secondary cell wall (SCW) formation was promoted in poplar stem xylem by the chimeric overexpression of OsSWN1 [22]
Summary
Lignin is a major chemical component of cell walls in terrestrial plant biomasses. This phenolic polymer is mainly built from three monolignols, p-coumaryl, coniferyl, and sinapyl alcohols, which are biosynthesized from phenylalanine or tyrosine via the cinnamate/monolignol pathway [1, 2]. Lignin exhibits various essential roles for plant growth and development, it is highly resistant to chemical and biochemical pretreatment for the efficient utilization of the plant cell wall as lignocellulosic biomass [5]. Even for partial removal of lignin from the lignocellulosic biomass, especially woody biomass, material processing generally requires a substantial amount of energy and chemical consumption
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