Production and characterization of genetically lignin-modified Eucalyptus

Abstract:

In the pulp and paper industry, lignin must be removed by harsh chemical treatments, which is a costly process both to the mill and the environment. Our research purpose is to produce woody plants with high level of cellulose content.
We identified a cDNA encoding the transcription factor, Ntlim1 from tobacco (Nicotiana tabacum) that specifically binds a PAL-box sequence. The transgenic tobacco plants with antisense Ntlim1 showed low level of transcripts from several key phenylpropanoid pathway genes such as, phenylalanine ammonia-lyase, hydroxycinnamate CoA ligase and cinnamyl alcohol dehydrogenase. A 27% reduction of lignin content was observed in the transgenic tobacco with antisense Ntlim1. The antisense Ntlim1 construct with kanamycin resistant gene was also introduced into Eucalyptus camaldulensis that is one of the most important hardwood for afforestration. The transgenic Eucalyptus plants grown in the greenhouse, showed decreased expression levels of lignin biosynthesis genes. Forty-five independent primary transgenic plants were produced and all lines contained the T-DNA by PCR analysis. Subsequently, fifteen lines were screened by measuring the 4CL activity levels in the stems and were grown in the greenhouse. No remarkable abnormal growth was found in the transgenic lines. The lignin content of the cell wall residue (CWR) of stem xylem tissues was measured by the gravimetric Klason procedure. Lignin determinations were carried out on fifteen transgenic lines after 4 months of growth in the greenhouse. About 20% reductions of lignin content were observed in several lines. We succeeded the production of transgenic woody plants with significant reduction of lignin content and increase of holocellulose. We will discuss the characterization of the transgenic woody plants.