Antisense Inhibition of Tomato Fruit Sucrose Synthase Decreases Fruit Setting and the Sucrose Unloading Capacity of Young Fruit

Abstract

The role of sucrose synthase (SuSy) in tomato fruit was studied in transgenic tomato ( Lycopersicon esculentum ) plants expressing an antisense fragment of fruit-specific SuSy RNA ( TOMSSF ) under the control of the cauliflower mosaic virus 35S promoter. Constitutive expression of the antisense RNA markedly inhibited SuSy activity in flowers and fruit pericarp tissues. However, inhibition was only slight in the endosperm and was undetectable in the embryo, shoot, petiole, and leaf tissues. The activity of sucrose phosphate synthase decreased in parallel with that of SuSy, but acid invertase activity did not increase in response to the reduced SuSy activity. The only effect on the carbohydrate content of young fruit was a slight reduction in starch accumulation. The in vitro sucrose import capacity of fruits was not reduced by SuSy inhibition at 23 days after anthesis, and the rate of starch synthesized from the imported sucrose was not lessened even when SuSy activity was decreased by 98%. However, the sucrose unloading capacity of 7-day-old fruit was substantially decreased in lines with low SuSy activity. In addition, the SuSy antisense fruit from the first week of flowering had a slower growth rate. A reduced fruit set, leading to markedly less fruit per plant at maturity, was observed for the plants with the least SuSy activity. These results suggest that SuSy participates in the control of sucrose import capacity of young tomato fruit, which is a determinant for fruit set and development.

Comparison of a novel tomato sucrose synthase, SlSUS4, with previously described SlSUS isoforms reveals distinct sequence features and differential expression patterns in association with stem maturation

“…This apparently contributed to previous research focusing on fruit development and carbohydrate levels. Antisense expression of SlSUS1 under a constitutive promoter was found to decrease fruit setting and signiWcantly lower sucrose unloading in middle to late fruit development (D'Aoust et al 1999). However, under the control of a fruit-speciWc promoter, the same antisense expression was reported to have no eVect on fruit development (Chengappa et al 1999).…”

Transgenic alfalfa (Medicago sativa) with increased sucrose phosphate synthase activity shows enhanced growth when grown under N2-fixing conditions

“…The root nodule is not only a C sink, but is also the source of fixed nitrogen, making this a unique organ (White et al 2007). Sucrose synthase (SucSy) activity is positively correlated with sink strength in several plant species (D'Aoust et al 1999;Tang and Sturm 1999;Zrenner et al 1995;Coleman et al 2009) and the enzyme is vital for proper nodule function (Baier et al 2007). The root nodules of the SPS transformants showed an increase in the level of SucSy suggesting an increase in the transport of Suc from the leaves.…”

Sugarbeet sucrose synthase genes differ in organ-specific and developmental expression

“…A positive association between sucrose synthase activity, sink size and sucrose import has been demonstrated in many plant sink organs, and roles in carbohydrate partitioning, sink-source relations, and phloem loading and unloading have been proposed Zrenner et al, 1995;D'Aoust et al, 1999).…”