Expression of Candidate Marker Genes of Sugar Starvation is Enhanced in Growth-Suppressed Parthenocarpic Cucumber Fruit

Abstract Background In plant, sugar starvation occurs in many stress conditions. Although the involvement plant hormones is known, the underlying mechanism of fruit parthenocarpy is not known. Investigation of sugar starvation in growth suppressed parthenocarpic fruit may shed light on the parthenocarpy mechanism.Method Cucumber (Cucumis sativus L.) fruits were followed and harvested at 0, 2, 4, 6, 8 days after anthesis, and the expression of eight candidate marker genes of sugar starvation and sugar concentration were examined.Results A growth analysis of fruits showed variability in the onset of exponential growth. Fruits in which growth was suppressed for more than 8 days after anthesis tended to abort. The variation in transcript levels was very high. The correlation matrix of the transcript level of the genes and the time course of the expression of the eight genes led to their classification into three groups. This varying pattern of gene expression may reflect the dynamics of parthenocarpic fruit. Moreover, the gene expression patterns and hexose concentration suggested that sugar starvation occurs in parthenocarpic fruit in which growth is suppressed. Therefore, the asparagine synthetase gene and the Cucumis sativus Somatic Embryogenesis Zinc Finger 1 (CsSEF1), Cucumis sativus Fruit Defoliation Induced 1 (CsFDI1), CsaV3_1G000860, CsaV3_3G041280, and CsaV3_3G023510 genes were regarded as good marker genes of sugar starvation.Conclusion The occurrence of sugar starvation suggests the low sink activity precedes the decline in fruit growth. This suggests the sink activity is the control point of parthenocarpic fruit set.