Abstract
Transgenic lines of the potato cultivar White Lady expressing the trehalose-6-phosphate synthase (TPS1) gene of yeast exhibit improved drought tolerance, but grow slower and have a lower carbon fixation rate and stomatal density than the wild-type. To understand the molecular basis of this phenomenon, we have compared the transcriptomes of wild-type and TPS1-transgenic plants using the POCI microarray containing 42,034 potato unigene probes. We show that 74 and 25 genes were up-, and down-regulated, respectively, in the mature source leaves of TPS1-transgenic plants when compared with the wild-type. The differentially regulated genes were assigned into 16 functional groups. All of the seven genes, which were assigned into carbon fixation and metabolism group, were up-regulated, while about 42% of the assigned genes are involved in transcriptional and post-transcriptional regulation. Expression of genes encoding a 14-3-3 regulatory protein, and four transcription factors were down-regulated in the TPS1-transgenic leaves. To verify the microarray results, we used RNA gel blot analysis to examine the expression of eight genes and found that the RNA gel blot and microarray data correlated in each case. Using the putative Arabidopsis orthologs of the assigned potato sequences we have identified putative transcription binding sites in the promoter region of the differentially regulated genes, and putative protein-protein interactions involving some of the up- and down-regulated genes. We have also demonstrated that starch content is lower, while malate, inositol and maltose contents are higher in the TPS1-transgenic than in the wild-type leaves. Our results suggest that a complex regulatory network, involving transcription factors and other regulatory proteins, underpins the phenotypic alterations we have observed previously in potato when expressing the TPS1 gene of yeast.
Highlights
One major approach to improve drought tolerance in crop species is to express genes encoding either metabolic enzymes or transcription factors, which exert their effects through various mechanisms of action [1]
Trehalose-6phosphate (T6P) is synthesised from glucose-6-phosphate (G6P) and UDP-glucose (UDPG) by trehalose phosphate synthase (TPS) and T6P is converted into trehalose by trehalose phosphatase (TPP)
In a previous paper we have reported that introducing the TPS1 gene of yeast into S. tuberosum cv
Summary
One major approach to improve drought tolerance in crop species is to express genes encoding either metabolic enzymes or transcription factors, which exert their effects through various mechanisms of action [1]. Genes of different origins involved in trehalose metabolism have been used in a number of plant species to improve their drought tolerance [2]. In the yeast Saccharomyces cerevisiae, an enzyme complex, consisting of trehalose-6-phosphate synthase (TPS) and trehalose6-phosphate phosphatase (TPP) encoded by the genes TPS1 and TPS2, respectively, is involved in the synthesis of trehalose, while in Escherichia coli the corresponding genes are otsA and otsB. Ectopic expression of TPS1 and otsA in different plant species and overexpression of AtTPS1 in Arabidopsis improved drought tolerance, but had diverse effects on plant development and resulted in other phenotypic changes in certain species [2,3]
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