Reduced sedoheptulose-1,7-bisphosphatase levels in transgenic tobacco lead to decreased photosynthetic capacity and altered carbohydrate accumulation

Abstract

Transgenic tobacco (Nicotiana tabacum L. cv. Samsun) plants with reduced levels of the Calvin cycle enzyme sedoheptulose-1,7-bisphosphatase (SBPase; EC 3.1.3.37) were produced using an antisense construct in which the expression of a tobacco SBPase cDNA clone was driven by the cauli¯ower mosaic virus (CaMV) promoter. The reduction in SBPase protein levels observed in the primary transformants correlated with the presence of the antisense construct and lower levels of the endogenous SBPase mRNA. No changes in the amounts of other Calvin cycle enzymes were detected using Western blot analysis. The SBPase antisense plants with less than 20% of wild-type SBPase activity were observed to display a range of phenotypes, including chlorosis and reduced growth rates. Measurements of photosynthesis, using both light-dosage response and CO 2 response curves, of T1 plants revealed a reduction in carbon assimilation rates, which was apparent in plants retaining 57% of wild-type SBPase activity. Reductions were also observed in the quantum eciency of photosystem II. This decrease in photosynthetic capacity was re¯ected in a reduction in the carbohydrate content of leaves. Analysis of carbohydrate status in fully expanded source leaves showed a shift in carbon allocation away from starch, whilst sucrose levels were maintained in all but the most severely aected plants. Plants with less than 15% of wild-type SBPase activity were found to contain less than 5% of wild-type starch levels. The results of this preliminary analysis indicate that SBPase activity may limit the rate of carbon assimilation.Abbreviations: A = rate of CO 2 assimilation; CaMV = cauliower mosaic virus; C i = intercellular CO 2 concentration; FBPase = fructose-1,6-bisphosphatase; GAPDH = glyceraldehyde-3-phosphate dehydrogenase; LSU = large subunit; PRKase = phosphoribulokinase; RuBP = ribulose-1,5-bisphosphate; SBP = sedoheptulose-1,7-bisphosphate; SBPase = sedoheptulose-1,7-bisphosphatase Correspondence to: C.A. Raines;

Transgenic Tobacco Plants Overexpressing Chloroplastic Ferredoxin-NADP(H) Reductase Display Normal Rates of Photosynthesis and Increased Tolerance to Oxidative Stress

“…In most cases, progeny were not uniform and varied in the amount of FNR accumulated, suggesting that multiple transgene copies inserted at different loci were segregating. This behavior has frequently been observed using other transgenic plants (Stitt et al, 1991;Harrison et al, 1998;Hajirezaei et al, 2002). Representative segregation patterns of three independent lines displaying low (pFNR-1), high (pFNR-3), or variable (pFNR-2) reductase levels are shown in Figure 1C.…”

“…As a consequence, decreases in protein levels caused by the introduction of antisense RNA in transgenic plants are partially compensated by further activation of the extant enzyme molecules, resulting in attenuation of the inhibitory effects. For example, rates of photosynthesis were not strongly affected until the content of Rubisco (Stitt et al, 1991;Hudson et al, 1992), aldolase (Haake et al, 1998), plastidic Fru-1,6-bisphosphatase (Kossmann et al, 1994), sedoheptulose-1,7-bisphosphatase (Harrison et al, 1998), and phosphoribulokinase (Paul et al, 1995) was reduced to 50% or less of their wild-type levels. Moreover, the effects usually became significant only under saturating CO 2 and illumination (Stitt et al, 1991).…”

A moderate decrease of plastid aldolase activity inhibits photosynthesis, alters the levels of sugars and starch, and inhibits growth of potato plants

“…As oulined in the Introduction, photosynthesis was slightly more sensitive to a decrease of Rubisco (Masle et al, 1993;Stitt and Schulze, 1994) and SBPase (Harrison et al, 1997) in tobacco, but less sensitive to decreased expression of the NADP-GAPDH in tobacco (Price et al, 1995) or decreased expression of plastid FBPase in potato and PRK in tobacco (Paul et al, 1995).…”

“…Comparison of Figure 3(d) and Figure 5(a, e) shows that photosynthesis is inhibited in the aldolase transformants before FBPase activity falls this far. Antisense inhibition of SBPase activity had a stronger effect on photosynthesis (Harrison et al, 1997) but the inhibition of photosynthesis in the aldolase transformants cannot be due to low SBPase activity, because ambient photosynthesis was affected more strongly than SBPase activity (compare Figure 5a, e with Figure 3e). …”

Identification and characterization of cytosolic fructose-1,6-bisphosphatase in Euglena gracilis

“…Identification and characterization of cytosolic fructose-1,6-bisphosphatase in Euglena gracilis Takahisa Ogawa 1,2 , Ayako Kimura 1,2 , Harumi Sakuyama 1,2 , Masahiro Tamoi 1,2, *, Takahiro Ishikawa 2,3 and Shigeru Shigeoka…”