Expression of genes encoding carbohydrate-metabolic enzymes during taproot development in sugar beet (Beta vulgaris subsp. vulgaris)

In sugar beet (Beta vulgaris subsp. vulgaris, Chenopodiaceae), sucrose is stored in a taproot developed by a genus-specific type of anomalous secondary thickening from supernumerary cambial rings. In a previous study (Jammer & al. 2020), we showed that the transition from primary root development to the formation of the sucrose-storing taproot is accompanied by a clear shift in physiological signatures: characteristic changes in the activities of several key enzymes of carbohydrate metabolism were associated with the onset of taproot development and sucrose storage, resulting in three distinct physiological stages (prestorage, transition, secondary growth and sucrose storage). In order to investigate the regulatory mechanisms behind these changes in enzyme activities, we performed a microarray expression analysis for the genes encoding the respective carbohydrate-metabolic enzymes. The data obtained from the microarray were validated for selected transcripts by semi-quantitative reverse transcription PCR. A high level of similarity between the developmental changes in transcript levels and enzyme activities at the transition stage suggests that the majority of the respective enzymes are predominantly regulated on the transcriptional level during the early stages of taproot development.