Expression of a gene encoding a functional glycosyl hydrolase, trehalase, from Nicotiana tabacum in Saccharomyces cerevisiae

Trehalases (TREs) function in trehalose hydrolysis and commonly found in most organisms. It is said that most fungi have two types of TREs, acid trehalase and neutral trehalase, but other organisms including plants have only one type. To investigate the function of TRE from plants, a full-length cDNA clone encoding TRE was isolated and designated NtTRE. A conserved region of common trehalase can be found in deduced amino acid sequence of NtTRE, thus the gene was recognized to encode NtTRE enzyme. The NtTRE was expressed in Escherichia coli as a glutathione-S-transferase (GST)-fusion protein to investigate the function of the expressed protein as trehalase. SDS-PAGE profile of the protein extract of E. coli showed that the expressed GST-NtTRE protein appeared to be cleaved into two polypeptides, which were approximately 56 and 28 kDa in size, and to form an inclusion body. Based on the results of N-terminal amino acid sequencing of the 56-kDa protein, it contained almost all parts of NtTRE protein. Thus, the protein expressed in E. coli was used only for production of anti-NtTRE antibodies. Function of NtTRE was investigated using yeast expressing NtTRE. The NtTRE protein was expressed as a soluble protein. Trehalase activity of protein extract of the transformed yeast was significantly higher than that of control yeast carrying an empty vector. In addition, intracellular trehalose content in yeast cells was significantly reduced by expression of NtTRE. Those data provided a possibility to construct a modified tobacco plant that can accumulate trehalose in the cells by suppression of the expression and/or the activity of NtTRE.