Plant Genetics Advance Boosts Biofuels

Tuesday, January 6, 2015 @ 10:01 AM gHale

Plant geneticists figured out the gene networks that control cell wall thickening by the synthesis of the three polymers, cellulose, hemicellulose and lignin.

What that means is the most rigid of the polymers, lignin, represents “a major impediment” to extracting sugars from plant biomass that can make biofuels. This genetic advance could “serve as a foundation for understanding the regulation of a complex, integral plant component” and as a map for how future researchers might manipulate the polymer-forming processes to improve the efficiency of biofuel production.

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The three key components, found in plant tissues known as xylem, provide plants with mechanical strength and waterproof cells that transport water. Working in the model plant Arabidopsis thaliana, Sam Hazen at the University of Massachusetts Amherst and Siobhan Brady at the University of California, Davis, explored how a large number of interconnected transcription factors regulate xylem and cell wall thickening.

By understanding how the relative proportions of these biopolymers end up controlled in plant tissue would open up opportunities to redesign plants for biofuel use. Hazen and Brady’s study identified hundreds of new regulators.

Specifically, using a systems approach to identify protein-DNA interactions, the researchers screened more than 460 transcription factors expressed in root xylem to explore their ability to bind the promoters of about 50 genes known to be in processes that produce cell-wall components. “This revealed a highly interconnected network of more than 240 genes and more than 600 protein-DNA interactions that we had not known about before,” Hazen said.

They also found each cell-wall gene in the xylem regulatory network ends up bound by an average of five different transcription factors from 35 distinct families of regulatory proteins. Further, many of the transcription factors form a surprisingly large number of feed-forward loops that co-regulate target genes.

In other words, rather than a series of on-off switches that leads to an ultimate action like making cellulose, most of the proteins including regulators of cell cycle and differentiation bind directly to cellulose genes and to other transcription regulators. This gives plants a huge number of possible combinations for responding and adapting to environmental stress such as salt or drought, the researchers said.

While this study could identify interactive nodes, the techniques used were not able to let the authors determine exactly what types of feed forward loops are present in the xylem regulatory network. However, the work offers a framework for future research that should allow researchers to identify ways to manipulate this network and engineer energy crops for biofuel production.

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