Image courtesy of Daniel Cosgrove
Polymeric sugars called Xyloglucans (black lines) were thought to tether cellulose microfibrils (red lines) in primary cell walls (top panel). New results indicate a different arrangement, with load-bearing xyloglucans hidden in tight junctions that bind microfibrils together.
Results suggest a structurally important plant cell wall component intertwines with other wall components in an unpredicted way, interfering with access of enzymes used to break down plant biomass.
Provides new insights into plant cell wall structure and suggests innovative ways to enhance plant growth and efficiently convert biomass to biofuels. Also explains why some approaches for cell wall digestion do not work.
Growing plant cells are surrounded by a primary cell wall consisting predominantly of polymers of sugars (cellulose, hemicellulose, and pectin). Xyloglucan, typically referred to as hemicellulose, is widely believed to act as a tether between cellulose fibers, limiting cell enlargement and regulating cell wall mechanical properties. To test this model, Center for Lignocellulose Structure and Formation EFRC researchers at Pennsylvania State University assessed the biomechanical properties of the cell wall. Experiments examined the ability of primary cell walls to undergo creep — irreversible increases in the length of the walls due to loosening of the connections between cell wall components — in response to three types of enzymes, termed endoglucanases, that causes breakdown(hydrolysis) of either xyloglucan, cellulose, or both. The xyloglucan-specific and cellulose-specific endoglucanases, either by themselves or in combination, failed to induce creep; endoglucanases that hydrolyze both xyloglucan and cellulose induced a high creep rate and were able to break down the cell wall. These results suggest xyloglucan does not act as a load-bearing tether between cellulose microfibrils. Rather, a minor xyloglucan component may be located in the limited regions of tight contact between cellulose fibers, playing an important role in wall mechanics.
Director of the Center for Lignocellulose Structure and Formation EFRC
DOE Office of Science, Basic Energy Sciences, Energy Frontier Research Centers (EFRC) Program
Park, Yong Bum; Cosgrove, Daniel “A Revised Architecture of Primary Cell Walls Based on Biomechanical Changes Induced by Substrate-Specific Endoglucanases”Plant Physiol., 158, 1933-1943 (2012). [DOI: 10.1104/pp.111.192880]
Center for Lignocellulose Structure and Formation EFRC