Simultaneous Suppression of Lignin, Tricin and Wall-Bound Phenolic Biosynthesis via the Expression of Monolignol 4-O-Methyltransferases in Rice
CABBI Theme: Feedstock Production
Keywords: Biomass Analytics, Genome Engineering
Citation
Dwivedi, N., Yamamoto, S., Zhao, Y., Hou, G., Bowling, F., Tobiamtsu, Y., Liu, C.J. Oct. 5, 2023. “Simultaneous Suppression of Lignin, Tricin, and Wall-Bound Phenolic Biosynthesis via Expression of Monolignol 4-O-Methyltransferases in Rice.” Plant Biotechnology Journal. DOI: 10.1111/pbi.14186.
Phenotypic analysis of MOMT4 and MOMT9 transgenic plants. (a) Expression cassette of MOMT4/9 under OsC4H promoter with OsC4H 5′ untranslated region, a kozak sequence and a sorghum heat shock protein gene terminator (SbHSP). (b) The RT-PCR analysis of MOMT4/9 transgene expression in the WT, empty VC, MOMT4, or MOMT9 overexpression lines. Rice ubiquitin 5 gene (UBQ5) was used as the control. (c) Morphology of the regenerated 1.5-month-old MOMT4 and MOMT9 overexpression plants in T0 generation after first time cutting. Scale bar = 10 cm. (d and e) The measurements of plant height (d) and aerial biomass yield (e).
Overview
Grass lignocelluloses feature complex compositions and structures. In addition to the presence of conventional lignin units from monolignols, acylated monolignols and flavonoid tricin also incorporate into lignin polymer; moreover, hydroxycinnamates, particularly ferulate, cross-link arabinoxylan chains with each other and/or with lignin polymers. These structural complexities make grass lignocellulosics difficult to optimize for effective agro-industrial applications. In the present study, we assess the applications of two engineered monolignol 4-O-methyltransferases (MOMTs) in modifying rice lignocellulosic properties. Two MOMTs confer regiospecific para-methylation of monolignols but with different catalytic preferences. The expression of MOMTs in rice resulted in differential but drastic suppression of lignin deposition, showing more than 50% decrease in guaiacyl lignin and up to an 90% reduction in syringyl lignin in transgenic lines. Moreover, the levels of arabinoxylan-bound ferulate were reduced by up to 50%, and the levels of tricin in lignin fraction were also substantially reduced. Concomitantly, up to 11 μmol/g of the methanol-extractable 4-O-methylated ferulic acid and 5–7 μmol/g 4-O-methylated sinapic acid were accumulated in MOMT transgenic lines. Both MOMTs in vitro displayed discernible substrate promiscuity towards a range of phenolics in addition to the dominant substrate monolignols, which partially explains their broad effects on grass phenolic biosynthesis. The cell wall structural and compositional changes resulted in up to 30% increase in saccharification yield of the de-starched rice straw biomass after diluted acid-pretreatment. These results demonstrate an effective strategy to tailor complex grass cell walls to generate improved cellulosic feedstocks for the fermentable sugar-based production of biofuel and bio-chemicals.
Data
- MOMT4 and MOMT9 activities
- Study primers