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Increase of lysine and threonine in potato tubers and the effect of this accumulation on the expression of other potato tuber genes

Lysine levels have been increased in potato tubers by introduction of a bacterial dihydrodipicolinate synthase (bacterial DHPS; DapA) driven by the CaMV 35S promoter or the potato tuber-specific gbss promoter. Introduction of a mutant bacterial aspartate kinase (LysC) led to potato plants with increased levels of threonine and a small increase of methionine. The bacterial enzymes are feedback insensitive for the end product amino acids unlike the plant enzymes. In the Opti-2 project, plants with elevated levels of lysine, methionine, or threonine were used for further characterisation of the influence of the transgenes on gene expression of other genes via transcriptomics and proteomics methodologies.

A dedicated potato microarray was used to study the influence of the transgene in general and to find new genes involved in the regulation of the aspartate pathway or genes differentially expressed as a result of the accumulation of the aminoacids themselves. Proteomics tools such as two-dimensional gel electrophoresis, protein gel patterns comparison and LC-QTOF MS/MS protein sequencing were used in addition to analyse differences in protein expression between transgenic and wild type potato tubers.

The analyses showed that the effect of increasing the amino acid level on the expression of other genes in tubers is very low. The differences between various harvests of the same plants or between different potato cultivars or different tuber tissues are much higher than between wt and transgenics. Only by using special search programs for comparable expression patterns, a small set of (regulatory) genes could be traced that show an increased expression in the transgenic plants compared to the control plants. These genes might be involved in (the regulation of) essential amino acid biosynthesis, and will be studied in more detail in the future.

Reported by

PLANT RESEARCH INTERNATIONAL
DROEVENDAALSESTEEG 1, PO BOX 16
6700AA WAGENINGEN
Netherlands
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