Journal Article

Coexistence but Independent Biosynthesis of Catechyl and Guaiacyl/Syringyl Lignin Polymers in Seed Coats

Chen, Fang, Escamilla-Treviño, Luis L., Tobimatsu, Yuki, Nakashima, Jin, Dixon, Richard A., Jackson, Lisa, Ralph, John

2013

Overview

Lignins are phenylpropanoid polymers, derived from monolignols, commonly found in terrestrial plant secondary cell walls. We recently reported evidence of an unanticipated catechyl lignin homopolymer (C lignin) derived solely from caffeyl alcohol in the seed coats of several monocot and dicot plants. We previously identified plant seeds that possessed either C lignin or traditional guaiacyl/syringyl (G/S) lignins, but not both. Here, we identified several dicot plants (Euphorbiaceae and Cleomaceae) that produce C lignin together with traditional G/S lignins in their seed coats. Solution-state NMR analyses, along with an in vitro lignin polymerization study, determined that ther is, however, no copolymerization detectable (i.e., that the synthesis and polymerization of caffeyl alcohol and conventional monolignols in vivo is spatially and/or temporally separated). In particular, the deposition of G and C lignins in Cleome hassleriana seed coats is developmentally regulated during seed maturation; C lignin appears successively after G lignin within the same testa layers, concurrently with apparent loss of the functionality of O-methyltransferases, which are key enzymes for the conversion of C to G lignin precursors. This study exemplifies the flexible biosynthesis of different types of lignin polymers in plants dictated by substantial, but poorly understood, control of monomer supply by the cells.

• Publisher: American Society of Plant Biologists
• Subject: Alcohols / biosynthesis / Biosynthetic Pathways / Cell Wall - chemistry / Cell Wall - enzymology / Cell Wall - metabolism / Cell walls / Cleomaceae / Cleome - chemistry / Cleome - enzymology / Cleome - metabolism / Euphorbiaceae / Euphorbiaceae - chemistry / Euphorbiaceae - enzymology / Euphorbiaceae - metabolism / Lignification / Lignin / Lignin - biosynthesis / Lignin - chemistry / Magnetic Resonance Spectroscopy / Magnoliopsida - chemistry / Magnoliopsida - enzymology / Magnoliopsida - metabolism / Methyltransferases - metabolism / Microscopy, Confocal / Molecular Structure / Monomers / Plant cells / Plants / Plants - chemistry / Plants - enzymology / Plants - metabolism / Polymerization / Polymers / Polymers - metabolism / seed coat / Seeds - enzymology / Seeds - metabolism / Species Specificity / Testa