Functional characterization of caffeic acid O-methyltransferase in internode lignification of switchgrass (Panicum virgatum)

Abstract

Caffeic acid O-methyltransferase (COMT) is a crucial enzyme that mainly methylates phenylpropanoid meta-hydroxyl of C₅ in the biosynthesis of syringyl lignin in angiosperms. A putative COMT, named as PvCOMT1, was isolated from switchgrass (Panicum virgatum), a C₄ warm-season dual-purpose forage and bioenergy crop. Our results showed that recombinant PvCOMT1 enzyme protein catalyzed the methylation of 5-OH coniferyl alcohol, 5-OH coniferaldehyde (CAld5H) and 5-OH ferulic acid. Further in vitro studies indicate that CAld5H can dominate COMT-mediated reactions by inhibiting the methylation of the other substrates. Transgenic switchgrass plants generated by an RNAi approach were further employed to study the function of COMT in internode lignification. A dramatic decrease in syringyl lignin units coupled with an obvious incorporation in 5-OH guaiacyl lignin units were observed in the COMT-RNAi transgenic plants. However, the constitutive suppression of COMT in switchgrass plants altered neither the pattern of lignin deposition along the stem nor the anatomical structure of internodes. Consistent with the biochemical characterization of PvCOMT1, a significant decrease in sinapaldehyde was found in the COMT-RNAi transgenic switchgrass plants, suggesting that CAld5H could be the optimal intermediate in the biosynthesis syringyl lignin.

Keywords

biofuel crop / caffeic acid O-methyltransferase / forage / lignin / Panicum virgatum / switchgrass / transgenic plant

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Supplementary materials

The online version of this article at https://doi.org/10.15302/J-FASE-2017198 contains supplementary material (Table S1).ƒƒ

Acknowledgements

We thank Dr. Fang Chen of Prof. Richard A. Dixon’s Laboratory, University of North Texas for kindly providing standard compounds. This research was supported by the “100-Talent Program of the Chinese Academy of Sciences” foundation, the National Natural Science Foundation of China (31470390), and the National Key Technologies Research & Development Program-Seven Major Crop Breeding Project (2016YFD0101803).

Compliance with ethics guidelines

Fengyan Wu, Zhenying Wu, Aiguo Yang, Shanshan Jiang, Zeng-Yu Wang, and Chunxiang Fu declare that they have no conflicts of interest or financial conflicts to disclose.ƒThis article does not contain any studies with human or animal subjects performed by any of the authors.

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The Author(s) 2018. Published by Higher Education Press. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0)