Antisense‐inhibition of ADP‐glucose pyrophosphorylase in developing seeds of Vicia narbonensis moderately decreases starch but increases protein content and affects seed maturation

Abstract

SummaryThe small subunit of a Vicia faba ADP-glucose pyrophosphorylase (AGP) cDNA was expressed in antisense orientation in Vicia narbonensis under the control of the seed-speci®c legumin B4 promoter. From several independent transgenic lines both ADP-glucose pyrophosphorylase AGP-mRNA and AGP enzyme activity were reduced by up to 95% in the cotyledons during the mid-to late-maturation phase. Starch was moderately decreased and sucrose was increased. In two of three lines, transcripts encoding the large subunit of AGP and the storage protein vicilin were increased, whereas legumin B-mRNA was decreased. Transcripts of other storage-associated genes were not altered. The cotyledons contained more protein and total nitrogen. Despite the reduction in starch, total carbon was not decreased and dry weight was unchanged. Compared to the wild type, transgenic seeds contained more water and accumulated dry weight during a longer period, and therefore had a prolonged seed-®lling period. Transgenic cotyledon cells of comparable age to the wild type were more highly vacuolated and contained smaller starch grains, indicating a delay in cellular differentiation. We conclude that a speci®c alteration in carbon metabolism can have pleiotropic effects on water and nitrogen content and induces temporal changes in seed development.

ADP-Glucose Pyrophosphorylase-Deficient Pea Embryos Reveal Specific Transcriptional and Metabolic Changes of Carbon-Nitrogen Metabolism and Stress Responses

“…Starch levels between 20 and 35 DAP were only reduced by approximately 50% (Supplemental Fig. S1), indicating a low control coefficient for pea seed AGP on starch synthesis, in accordance with what has already been reported for AGP-reduced Vicia seeds (Weber et al, 2000). In transgenic seeds, mRNA levels of the major storage protein vicilin were increased after 20 DAP, whereas those of legumin decreased to 40% of the wild-type level (Supplemental Fig.…”

“…In contrast to AGP-deficient Vicia seeds (Weber et al, 2000), seed fill duration was apparently unchanged in the transgenic plants described here, and, as a consequence of lower dry weight accumulation, final seed weight was decreased whereas the seed number per plant was unaltered (data not shown).…”

“…AGP-repressed pea seeds exhibit metabolic shifts in composition from starch toward the accumulation of sugars, lipids, and proteins, a phenotype already reported for AGP-repressed Vicia seeds (Weber et al, 2000;Rolletschek et al, 2002) and rb/rr pea mutants (Denyer et al, 1995). However, in iAGP-3 seeds, higher N-C ratios and N contents were partially compensated Figure 6.…”

“…Its overexpression in Vicia narbonensis seeds channels more C into organic acids, stimulates amino acid biosynthesis, and increases protein content (Rolletschek et al, 2004;Radchuk et al, 2007). Accumulation of Suc, as shown for AGP-repressed Vicia (Weber et al, 2000;Rolletschek et al, 2002) and maize (Cossegal et al, 2008) seeds, causes repartitioning of C into glycolysis, tricarboxylic acid (TCA) cycle, and amino acid biosynthesis.…”

Antisense-inhibition of ADP-glucose pyrophosphorylase in Vicia narbonensis seeds increases soluble sugars and leads to higher water and nitrogen uptake

“…We were able to show that transgenic cotyledons contained moderately decreased amounts of starch. Transgenic seeds accumulated dry weight during a longer time period and, therefore, had a prolonged seed-filling period (Weber et al 2000). The protein content was higher but it is unclear whether this was caused by altered carbon partitioning, nitrogen uptake or to the longer seed-filling period.…”