Antisense inhibition of plastidial phosphoglucomutase provides compelling evidence that potato tuber amyloplasts import carbon from the cytosol in the form of glucose‐6‐phosphate

Abstract

SummaryThe aim of this work was to establish whether plastidial phosphoglucomutase is involved in the starch biosynthetic pathway of potato tubers and thereby to determine the form in which carbon is imported into the potato amyloplast. For this purpose, we cloned the plastidial isoform of potato PGM (StpPGM), and using an antisense approach generated transgenic potato plants that exhibited decreased expression of the StpPGM gene and contained signi®cantly reduced total phosphoglucomutase activity. We con®rmed that this loss in activity was due speci®cally to a reduction in plastidial PGM activity. Potato lines with decreased activities of plastidial PGM exhibited no major changes in either whole-plant or tuber morphology. However, tubers from these lines exhibited a dramatic (up to 40%) decrease in the accumulation of starch, and signi®cant increases in the levels of sucrose and hexose phosphates. As tubers from these lines exhibited no changes in the maximal catalytic activities of other key enzymes of carbohydrate metabolism, we conclude that plastidial PGM forms part of the starch biosynthetic pathway of the potato tuber, and that glucose-6-phosphate is the major precursor taken up by amyloplasts in order to support starch synthesis.

Alteration of the Interconversion of Pyruvate and Malate in the Plastid or Cytosol of Ripening Tomato Fruit Invokes Diverse Consequences on Sugar But Similar Effects on Cellular Organic Acid, Metabolism, and Transitory Starch Accumulation

“…These constructs were subsequently introduced into tomato (Solanum lycopersicum) plants by the Agrobacterium tumefaciens-mediated transformation protocol. Plants were selected and maintained as described in the literature (Tauberger et al, 2000). For initial screening, eight RNAi-PEPCK lines and nine RNAi-ME lines were selected on the basis of PEPCK and NADP-ME1 gene expression by qRT-PCR.…”

Metabolic Profiling of Transgenic Tomato Plants Overexpressing Hexokinase Reveals That the Influence of Hexose Phosphorylation Diminishes during Fruit Development

“…Starch and sugars were determined spectrophotometrically as described by Fernie et al (2001a), and hexose phosphates were determined spectrophotometrically as detailed by Tauberger et al (2000). Nucleotides and nucleotide sugars were separated by HPLC on a Partisil-SAX anion-exchange column (P10SAX-250; Hichrom, Reading, UK) as described by Fernie at al.…”

Elucidation of the Biosynthetic Pathway of the Allelochemical Sorgoleone Using Retrobiosynthetic NMR Analysis

“…In most plant cells, exogenous acetate is not usually incorporated into C18 and shorter fatty acids because acetate does not readily cross the plastidic membranes, and plastids have their own endogenous pool of acetate used for fatty acid synthesis (32-34). Even when endogenous acetate has been reported to be incorporated in short fatty acids, glucose has been demonstrated to be a far better substrate, because it can either be imported in nongreen plastids directly as glucose 6-phosphate and used as the source for the plastidic pool of acetate (35,36) or be broken down to triose phosphates in the cytosol and taken up in plastids via triose phosphate translocators (37).…”