报告摘要：After elucidating functions of several key lignin biosynthesis pathway genes in poplar genome and modifying lignin content and structure in transgenic Populus trees, over two decades ago, our group at Michigan Tech initiated research into how trees synthesize cellulose in their secondary cell walls. Our initial interest was focused on improving cellulose synthesis in trees for paper and pulp products but recently cellulosic biofuels have become important as a part of global bioenergy agenda. Wood cellulosic resources are expected to provide renewable raw materials for sustainable biofuel production. Bioconversion of cellulose to ethanol, however, is hampered by numerous intractable problems. Therefore, we are discovering innovative ways of improving cellulosic biomass production in trees themselves for efficient bioethanol production. We want to first decipher and then re-engineer the process of cellulose biosynthesis occurring inside the woody cell walls in poplar trees.
We are taking a multi-pronged approach to unravel the process of cellulose biosynthesis in trees. First, we cloned and characterized several cellulose synthase, sucrose synthase and Korrigan cellulase genes from poplars. All these genes are known to be important for cellulose synthesis in herbaceous model plants. Second, single or simultaneous genetic manipulation of some of these genes in transgenic poplar trees have produced interesting phenotypes ranging from increase in the cellulose content to significant decrease (>75%) in wood cellulose amounts. These alterations in cellulose were also accompanied by significant changes in hemicelluloses and lignin contents. Such cellulose deficient trees changed their growth habit and became weak creepers. Third, by using whole poplar genome microarrays, we have monitored the changes in gene expression patterns in tension wood system where cellulose content and properties are drastically changed compared to normal wood. The gelatinous or G layers in tension wood fibers lack lignin and are made up of almost pure cellulose (98.5%). This approach has provided a host of candidate genes that could be manipulated for cellulose production with novel properties. Finally, we have developed a virus induced gene silencing (VIGS) system to rapidly screen and identify hitherto unknown genes involved in cell wall development with the hope to translate that knowledge to poplar trees. As a proof of concept, expression of several known genes involved in cellulose, hemicellulose and lignin biosynthesis was transiently suppressed in tobacco and a clear impact on synthesis of respective polymers was demonstrated. An update on present status of knowledge in this field will also be presented. Our long-term goal is to unravel the basic process of cellulose biosynthesis in trees in order to enable economically viable and ecologically sustainable utilization of bioenergy.