Making “Better” Plant Cell Walls

The Science

To identify genes controlling secondary cell wall biosynthesis in the model legume Medicago truncatula, researchers screened a Tnt1 retrotransposon insertion mutant population for plants with altered patterns of lignin autofluorescence. From more than 9000 R1 plants screened, four independent lines were identified with a total lack of lignin in the interfascicular region. The mutants also showed loss of lignin in phloem fibers, reduced lignin in vascular elements, failure in anther dehiscence and absence of phenolic autofluorescence in stomatal guard cell walls. Microarray and PCR analyses confirmed that the mutations were caused by the insertion of Tnt1 in a gene annotated as encoding a NAM (no apical meristem)-like protein (here designated Medicago truncatula NAC SECONDARY WALL THICKENING PROMOTING FACTOR 1, MtNST1). MtNST1 is the only family member in Medicago, but has three homologs (AtNST1–AtNST3) in Arabidopsis thaliana, which function in different combinations to control cell wall composition in stems and anthers. Loss of MtNST1 function resulted in reduced lignin content, associated with reduced expression of most lignin biosynthetic genes, and a smaller reduction in cell wall polysaccharide content, associated with reduced expression of putative cellulose and hemicellulose biosynthetic genes. Acid pre-treatment and cellulase digestion released significantly more sugars from cell walls of nst1 mutants compared with the wild type.


The lignocellulosic materials that comprise the secondary cell walls of plants provide sugars for fermentation to second generation biofuels. This rigid material provides structural support for plant and a means by which they resist pathogens and other stresses, but this same strength makes it difficult and expensive to degrade into sugars for the fermentation and production of biofuels. Researchers at the DOE Bioenergy Sciences Center (BESC) have identified a gene in the model legume Medicago truncatula (barrel medic) that is involved in secondary cell wall thickening. Plants containing a mutant form of this gene exhibited reduced lignin content, altered cell walls, and unopened anthers. When subjected to chemical and enzyme treatments, these mutants released significantly more sugars for fermentation than the wild type. Additionally, since pollen is not released from the anthers, seed development in this self-pollinating plant is prevented, providing a natural means of preventing the unwanted spread of this plant in nature. These desirable features suggest that this gene would be a good target for genetic engineering for plant feedstock improvement. The research was carried out at Oak Ridge National Laboratory, lead institution for BESC, and with their partners at the Samuel Roberts Noble Foundation and the National Renewable Energy Laboratory (NREL).

Principal Investigator

Richard A. Dixon

BER Program Manager

Kari Perez

U.S. Department of Energy, Biological and Environmental Research (SC-33)
Biological Systems Science Division
[email protected]


Zhao, Q., Gallego-Giraldo, L., Wang H., Zeng Y., Ding S.-H., Chen, F, and Dixon, R. A. 2010. “An NAC Transcription Factor Orchestrates Multiple Features of Cell Wall Development in Medicago truncatula,Plant Journal 63(1), 100–114. DOI:10.1111/j.1365-313X.2010.04223.x.