ARS | Publication request: CHARACTERIZATION OF A p-COUMAROYL TRANSFERASE RESPONSIBLE FOR THE INCORPORATION OF pCA INTO GRASS CELL WALLS

Submitted to: Meeting Abstract
Publication Type: Abstract
Publication Acceptance Date: May 15, 2008
Publication Date: August 25, 2008
Citation: Hatfield, R.D., Marita, J.M. 2008. Characterization of a p-coumaroyl transferase responsible for the incorporation of pCA into grass cell walls [abstract]. Ferulate '08: An International Conference on Hydroxycinnamates and Related Plant Phenolics, August 25-27, 2008, Minneapolis, Minnesota. p. 53.

Technical Abstract: Grasses form unique acylated lignins involving p-coumarate (pCA) residues primarily linked to syringyl units in lignin. A p-coumaroyl transferase (pCAT) is responsible for incorporation of pCA into cell walls as pCA-monolignol conjugates. Conjugates are synthesized in the cytoplasm, shuttled out into the wall, and incorporated into lignin. The pCAT of interest is a soluble enzyme that utilizes p-coumaroyl-CoA (pCA-CoA) as the activated donor molecule and sinapyl alcohol as the preferred acceptor molecule. A robust assay, based on GC-MS, allows for rapid assessment and authentication of transferase activity in tissue extracts. Evaluation of a spectrum of warm season (C4) and cool season (C3) grasses for the degree of acylation indicated marked differences. However, there was not a distinction between C4 and C3 grasses regarding levels of acylation. Acylation of lignin by pCA ranged from 10.7 (bromegrass ¿ Bromus inermis, C3) to 37.7 (corn - Zea mays L., C4) mg/g cell wall (CW). Two C4 grasses corn and grain sorghum (Sorghum bicolor L.) had the highest levels of acylation but other C4 species, such as switchgrass and little bluestem, were more similar to C3 grasses. Lignin ranged from 163 (bromegrass, C3) to 222 (corn, C4) mg/g CW among the grass species evaluated. Ester linked ferulates were more consistent among the grasses with ranges from 4.5 (oat - Avena sativa, C3) to 7.6 (sorghum, C4) mg/g CW. The pCAT activities among the grasses did not parallel the corresponding level of pCA incorporation into lignin. This was not surprising since previous work assessing the spatial and temporal distribution of the p-coumaroylation of corn lignin indicated unique developmental patterns in corn stem tissues. Levels of pCAT activity varied along the corn stem with the least activity in the lower most internode (closest to soil line) and maximum activity in internodes closest to the top of the plant that are undergoing rapid lignification. Understanding the molecular basis for modifications to lignin, such as p-coumaroylation, is key to developing strategies to improve total plant quality and utilization.