SummaryWood of broad‐leaf tree species is a valued source of renewable biomass for biorefinery and a target for genetic improvement efforts to reduce its recalcitrance. Glucuronoxylan (GX) plays a key role in recalcitrance through its interactions with cellulose and lignin. To reduce recalcitrance, we modified wood GX by expressing GH10 and GH11 endoxylanases from Aspergillus nidulans in hybrid aspen (Populus tremula L. × tremuloides Michx.) and targeting the enzymes to cell wall. The xylanases reduced tree height, modified cambial activity by increasing phloem and reducing xylem production, and reduced secondary wall deposition. Xylan molecular weight was decreased, and the spacing between acetyl and MeGlcA side chains was reduced in transgenic lines. The transgenic trees produced hypolignified xylem having thin secondary walls and deformed vessels. Glucose yields of enzymatic saccharification without pretreatment almost doubled indicating decreased recalcitrance. The transcriptomics, hormonomics and metabolomics data provided evidence for activation of cytokinin and ethylene signalling pathways, decrease in ABA levels, transcriptional suppression of lignification and a subset of secondary wall biosynthetic program, including xylan glucuronidation and acetylation machinery. Several candidate genes for perception of impairment in xylan integrity were detected. These candidates could provide a new target for uncoupling negative growth effects from reduced recalcitrance. In conclusion, our study supports the hypothesis that xylan modification generates intrinsic signals and evokes novel pathways regulating tree growth and secondary wall biosynthesis.

中文翻译：

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次生壁中木聚糖的修饰改变了细胞壁的生物合成和木材形成程序，并改善了糖化


摘要阔叶树种的木材是生物精炼厂可再生生物质的重要来源，也是遗传改良工作以减少其顽固性的目标。葡萄糖醛酸木聚糖 （GX） 通过与纤维素和木质素的相互作用在顽固性中起关键作用。为了减少顽固性，我们通过在杂交白杨 （Populus tremula L. ×. 3 tremuloides Michx.） 中表达来自构巢曲霉的 GH10 和 GH11 内多聚糖酶来修饰木材 GX，并将酶靶向细胞壁。木聚糖酶降低了树木高度，通过增加韧皮部和减少木质部的产生来改变形成层活性，并减少了次生壁沉积。转基因品系中木聚糖分子量降低，乙酰基和 MeGlcA 侧链之间的间距减小。转基因树产生木质部低下，具有薄的次生壁和变形的血管。未经预处理的酶促糖化葡萄糖产量几乎翻了一番，表明顽固性降低。转录组学、激素组学和代谢组学数据为细胞分裂素和乙烯信号通路的激活、ABA 水平的降低、木质化的转录抑制和次生壁生物合成程序的一个子集（包括木聚糖葡萄糖醛酸化和乙酰化机制）提供了证据。检测到几个感知木聚糖完整性受损的候选基因。这些候选者可以为将负增长效应与减少的顽固性脱钩提供新的靶点。总之，我们的研究支持木聚糖修饰产生内在信号并引发调节树木生长和次生壁生物合成的新途径的假设。