An emerging concept of diurnal variation in expression of UDP-Glucose Pyrophosphorylase gene, (StUGPase2), in potato (Solanum tuberosum L.)

Diurnal regulation of gene expression encoding the dominant isoform of UDP-Glucose Pyrophosphorylase, StUGPase2, was studied in potato leaves at different developmental stages (pre-tuberization, tuber initiation, and tuber bulking). Across the developmental stages, the StUGPase2 steady-state mRNA level increased gradually from morning (6 AM) to noon (12 PM), followed by a transient drop at 2 PM. The mRNA level increased thereafter, and the highest transcript abundance was recorded at 8:00 PM. A sharp decline in StUGPase2 transcript abundance at 2 PM in all the stages studied is believed to be associated with the previous reports of diurnal behaviour of sucrose concentration and light responsiveness of sucrose synthase enzyme. Moreover, in all three stages, a steady state increase of StUGPase2 transcript despite a consistent decrease in irradiance after 12 PM, suggests the presence of more complex transcriptional regulation. Comparatively higher StUGPase2 transcript abundance at the tuberization initiation stage as compared to the pre and post-tuberization stages indicates the prominent role of the gene during tuber development. Bioinformatics analysis of the StUGPase2 promoter region predicted the presence of various light-responsive cis-regulatory nucleotide sequences, which are considered to be associated with the light-mediated diurnal change in StUGPase2 gene expression. This research will aid in understanding the pattern of UGPase gene regulation, which is ultimately connected to potato tuber yield and bulking attributes.