Wood reinforcement of poplar by rice NAC transcription factor

Abstract

Lignocellulose, composed of cellulose, hemicellulose, and lignin, in the secondary cell wall constitutes wood and is the most abundant form of biomass on Earth. Enhancement of wood accumulation may be an effective strategy to increase biomass as well as wood strength, but currently only limited research has been undertaken. Here, we demonstrated that OsSWN1, the orthologue of the rice NAC Secondary-wall Thickening factor (NST) transcription factor, effectively enhanced secondary cell wall formation in the Arabidopsis inflorescence stem and poplar (Populus tremula×Populus tremuloides) stem when expressed by the Arabidopsis NST3 promoter. Interestingly, in transgenic Arabidopsis and poplar, ectopic secondary cell wall deposition in the pith area was observed in addition to densification of the secondary cell wall in fiber cells. The cell wall content or density of the stem increased on average by up to 38% and 39% in Arabidopsis and poplar, respectively, without causing growth inhibition. As a result, physical strength of the stem increased by up to 57% in poplar. Collectively, these data suggest that the reinforcement of wood by NST3pro:OsSWN1 is a promising strategy to enhance wood-biomass production in dicotyledonous plant species.

Change in lignin structure, but not in lignin content, in transgenic poplar overexpressing the rice master regulator of secondary cell wall biosynthesis

“…As revealed by previous and the present study, overexpression of OsSWN1 induces acceleration of secondary cell wall formation (Sakamoto et al ). However, molecular structure of lignin in the thickened cell walls had never been characterized quantitatively or qualitatively, except for the histochemical staining assay by Wiesner reagent, which reacts with cinnamaldehyde end‐group units present in lignin.…”

“…We also monitored the expressions of the genes for cellulose ( cellulose synthase A4 , CESA4 ) and xylan ( glycosyltransferase family 43A , GT43A ) biosynthesis. Significant increases in the expressions of CESA4 and GT43A were observed in both the transgenic lines, indicating that OsSWN1 can upregulate polysaccharide deposition in the secondary cell walls as has been observed in Arabidopsis (Sakamoto et al ).…”

“…To confirm the change in lignin structure in transgenic plants, we performed the following two chemical analyses: lignin determination by the acetyl bromide method and derivatization followed by reductive cleavage (DFRC) using cell wall residues derived from Lines #8 and #11. As shown in Table and as suggested by Py‐GC/MS analysis, no significant differences were observed in lignin content between the wild‐type and the transgenic plants, suggesting that overexpression of OsSWN1 induced the accelerated biosynthesis of both polysaccharides and lignin, as observed in transgenic Arabidopsis expressing OsSWN1 under control of the NST3/SND1 promoter (Sakamoto et al ).…”

“…Sakamoto et al () reported the characterization of transgenic poplar plants with gene construct NST3pro::OsSWN1‐VP16 , which can activate deposition of secondary cell wall in pith, xylem‐ and phloem‐fiber cells. Histochemical and physical analyses conducted during the present study allowed us to obtain various quantitative data from five independent transgenic poplar plants derived from five distinct transgenic events.…”

“…Hybrid aspen Populus tremula × Populus tremuloides (wild‐type strain T89) that had been generated in our previous study (Sakamoto et al ) was used in this study. Wild‐type and four independent transgenic lines (#3, #8, #11 and #24) were cultured in 0.5 × Murashige and Skoog medium (pH 5.7; Murashige and Skoog ) containing 0.8% (w/v) agar at 25°C under a cycle of 16 h light (50 μmol m −2 s −1 )/8 h dark.…”