Feedstock Development projects
Understanding Low-Temperature Limits of Miscanthus and Its Variation and Basis
Photosynthesis, which converts sunlight into stored chemical energy, occurs via several pathways, and C4 is the most efficient known. But unlike other photosynthetic pathways, it has been found vulnerable to low temperatures. However, the form of Miscanthus that is currently being widely tested by the EBI, Miscanthus x giganteus, is exceptional among C4 plants, being able to photosynthesize efficiently at almost 6 degrees C lower than corn, the most cold-tolerant of current C4 crops. This project is determining the basis of this higher low-temperature photosynthetic efficiency in order to help improve the plants and learn the molecular characters to search for in breeding Miscanthus, or even energy cane, for colder climates.
The photosynthetic enzyme PPDK has been found to increase in both cold adapted Miscanthus and the completely unrelated cold-tolerant C4 perennial bioenergy feedstock, Spartina pectinata (cordgrass). This suggests PPDK increase may be a common and easily assessed character in identifying cold-tolerant genotypes. Cold tolerance during growth is a key factor determining high productivity in C4 feedstocks in temperate production systems.
Analysis of the transcriptome of genes revealed 410 genes that were up-regulated as Miscanthus acclimates to low temperature. Over 200 of these transcripts are now annotated and strikingly all genes associated with photosynthesis are up-regulated. In parallel, new collections of the parent species M. sinensis spanning from the southernmost tip of Japan to the northernmost have been assessed. The northernmost collection showed very much higher rates of photosynthesis at low temperature, suggesting that low temperature tolerance in this species, was not the result of a single event but most likely a progressive change.
Partial examination of the leaf proteome (complement of proteins) shows that when corn is exposed to lower temperatures, its loss of photosynthetic capacity corresponds, among other things, to the loss of a key enzyme unique to the chloroplasts (photosynthetic factories) of C4 leaves, chloroplastic pyruvate-phosphate dikinas (PPDK). In Miscanthus exposed to lower temperatures PPDK shows a large increase. This increase in PPDK coincides with a large increase in the expression of the gene for PPDK at low temperature in Miscanthus, while the reverse occurs in corn. Using gene expression arrays, we have also examined other gene expression changes, beyond increases in transcripts for PPDK, that may be associated with the apparently unique ability of Miscanthus to acclimate to low temperature. Although some 300 genes show significant changes, most notable is an up-regulation of all of the genes on the arrays known to code for chloroplast proteins, and several genes coding for proteins involved in transport.
Published in 2009
Does Greater Leaf-Level Photosynthesis Explain the Larger Solar Energy Conversion Efficiency of Miscanthus Relative to Switchgrass? , Frank Dohleman, Emily Heaton, Andrew Leakey, Steve Long, Plant, Cell and Environment, 32, pp. 1525-1537, June 25, 2009.
More Productive Than Maize in the Midwest: How Does Miscanthus Do It? , Frank Dohleman and Steve Long, Plant Physiology, 150, pp. 2104-2115, June 17, 2009.