Wood 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.
- Klíčová slova
- Glucuronoxylan, fungal xylanases, lignocellulose, secondary cell wall, transgenic aspen, wood development,
- MeSH
- Aspergillus nidulans * genetika fyziologie MeSH
- buněčná stěna * chemie metabolismus MeSH
- dřevo * MeSH
- endo-1,4-beta-xylanasy metabolismus MeSH
- Populus * mikrobiologie fyziologie MeSH
- rostlinné buňky MeSH
- sacharin MeSH
- stromy fyziologie MeSH
- xylany * biosyntéza genetika MeSH
- Publikační typ
- časopisecké články MeSH
- Názvy látek
- endo-1,4-beta-xylanasy MeSH
- sacharin MeSH
- xylany * MeSH
Stem bending in trees induces flexure wood but its properties and development are poorly understood. Here, we investigated the effects of low-intensity multidirectional stem flexing on growth and wood properties of hybrid aspen, and on its transcriptomic and hormonal responses. Glasshouse-grown trees were either kept stationary or subjected to several daily shakes for 5 wk, after which the transcriptomes and hormones were analyzed in the cambial region and developing wood tissues, and the wood properties were analyzed by physical, chemical and microscopy techniques. Shaking increased primary and secondary growth and altered wood differentiation by stimulating gelatinous-fiber formation, reducing secondary wall thickness, changing matrix polysaccharides and increasing cellulose, G- and H-lignin contents, cell wall porosity and saccharification yields. Wood-forming tissues exhibited elevated jasmonate, polyamine, ethylene and brassinosteroids and reduced abscisic acid and gibberellin signaling. Transcriptional responses resembled those during tension wood formation but not opposite wood formation and revealed several thigmomorphogenesis-related genes as well as novel gene networks including FLA and XTH genes encoding plasma membrane-bound proteins. Low-intensity stem flexing stimulates growth and induces wood having improved biorefinery properties through molecular and hormonal pathways similar to thigmomorphogenesis in herbaceous plants and largely overlapping with the tension wood program of hardwoods.
- Klíčová slova
- Populus tremula × tremuloides, flexure wood, jasmonic acid signaling, mechanostimulation, polyamines, saccharification, thigmomorphogenesis, wood development,
- MeSH
- buněčná stěna metabolismus MeSH
- celulosa metabolismus MeSH
- dřevo * MeSH
- polyaminy analýza metabolismus farmakologie MeSH
- polysacharidy metabolismus MeSH
- Populus * genetika MeSH
- regulace genové exprese u rostlin MeSH
- Publikační typ
- časopisecké články MeSH
- Názvy látek
- celulosa MeSH
- jasmonic acid MeSH Prohlížeč
- polyaminy MeSH
- polysacharidy MeSH
