Disrupting Flavone Synthase II Alters Lignin and Improves Biomass Digestibility.

Pui Ying Lam,Shiro Suzuki,Yuki Tobimatsu,Toshiaki Umezawa,Clive Lo,Yuri Takeda,Masaomi Yamamura

doi:10.1104/pp.16.01973

Pui Ying Lam, Shiro Suzuki + Show 5 more

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https://doi.org/10.1104/pp.16.01973

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Journal: Plant physiology	Publication Date: Apr 6, 2017
Citations: 87	License type: cc-by

Affiliation: Kyoto University, University of Hong Kong

Abstract

Lignin, a ubiquitous phenylpropanoid polymer in vascular plant cell walls, is derived primarily from oxidative couplings of monolignols (p-hydroxycinnamyl alcohols). It was discovered recently that a wide range of grasses, including cereals, utilize a member of the flavonoids, tricin (3',5'-dimethoxyflavone), as a natural comonomer with monolignols for cell wall lignification. Previously, we established that cytochrome P450 93G1 is a flavone synthase II (OsFNSII) indispensable for the biosynthesis of soluble tricin-derived metabolites in rice (Oryza sativa). Here, our tricin-deficient fnsII mutant was analyzed further with an emphasis on its cell wall structure and properties. The mutant is similar in growth to wild-type control plants with normal vascular morphology. Chemical and nuclear magnetic resonance structural analyses demonstrated that the mutant lignin is completely devoid of tricin, indicating that FNSII activity is essential for the deposition of tricin-bound lignin in rice cell walls. The mutant also showed substantially reduced lignin content with decreased syringyl/guaiacyl lignin unit composition. Interestingly, the loss of tricin in the mutant lignin appears to be partially compensated by incorporating naringenin, which is a preferred substrate of OsFNSII. The fnsII mutant was further revealed to have enhanced enzymatic saccharification efficiency, suggesting that the cell wall recalcitrance of grass biomass may be reduced through the manipulation of the flavonoid monomer supply for lignification.

Highlights

Pui Ying Lam2, Yuki Tobimatsu2*, Yuri Takeda, Shiro Suzuki, Masaomi Yamamura, Toshiaki Umezawa, and Clive Lo*
The sequential condensation of p-coumaroylCoA with three malonyl-CoAs is catalyzed by chalcone synthase (CHS) and followed by isomerization by chalcone isomerase (CHI) to form naringenin, a flavanone that is the precursor for the biosynthesis of all the other classes of flavonoids
OsFNSII, along with its downstream OsC59H (Fig. 1), was expressed in leaf at the vegetative stage and in lemma and palea at the later stage of flower development, and several monolignol biosynthetic genes displayed similar spatial and temporal expression patterns (Supplemental Fig. S1). These data support our contention that OsFNSII is involved in the biosynthesis of soluble tricin metabolites and of tricin monomer for lignification in the major rice vegetative tissues, as demonstrated further below

Summary

Introduction

Pui Ying Lam, Yuki Tobimatsu2*, Yuri Takeda, Shiro Suzuki, Masaomi Yamamura, Toshiaki Umezawa, and Clive Lo*. A ubiquitous phenylpropanoid polymer in vascular plant cell walls, is derived primarily from oxidative couplings of monolignols (p-hydroxycinnamyl alcohols). It was discovered recently that a wide range of grasses, including cereals, utilize a member of the flavonoids, tricin (39,59-dimethoxyflavone), as a natural comonomer with monolignols for cell wall lignification. Our tricin-deficient fnsII mutant was analyzed further with an emphasis on its cell wall structure and properties. Chemical and nuclear magnetic resonance structural analyses demonstrated that the mutant lignin is completely devoid of tricin, indicating that FNSII activity is essential for the deposition of tricin-bound lignin in rice cell walls. The fnsII mutant was further revealed to have enhanced enzymatic saccharification efficiency, suggesting that the cell wall recalcitrance of grass biomass may be reduced through the manipulation of the flavonoid monomer supply for lignification. FNSII, and sequential hydroxylations and O-methylations at the flavone B-ring furnish tricin, which is further converted into the downstream tricin derivatives (Fig. 1)

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