Comparison of expression profiles in response to blue, UV-A, and UV-B in the swollen hypocotyls of turnip

UV-A mediated regulation of anthocyanin biosynthesis was investigated in swollen hypocotyls of the red turnip ‘Tsuda’. The shaded swollen hypocotyls which contained negligible anthocyanin were exposed to artificial light sources including low fluence UV-B, UV-A, blue, red, far-red, red plus UV-A, far-red plus UV-A, and blue plus red. Among these lights, only UV-A induced anthocyanin biosynthesis and co-irradiation of red or far-red with UV-A did not affect the extent of UV-A induced anthocyanin accumulation. The expression of phenylalanine ammonia lyase (PAL; EC 4.3.1.5), chalcone synthase (CHS; EC 2.3.1.74), flavanon 3-hydrocylase (F3H; EC 1.14.11.9), dihydroflavonol 4-reductase (DFR; EC 1.1.1.219) and anthocyanidin synthase (ANS; EC 1.14.11.-) genes were increased with time during a 24 hour exposure of UV-A. In contrast, irradiation of red, blue, UV-B, and a combination of blue with red failed to induce CHS expression. Microarray analysis showed that only a few genes, including chalcone synthase and flavanon 3-hydroxylase were induced significantly by UV-A, while a separate set of many genes was induced by low fluence UV-B. The UV-A specific induction of anthocyanin biosynthesis and the unique gene expression profile upon UV-A irradiation as compared with blue and UV-B demonstrated that the observed induction of anthocyanin biosynthesis in red turnips was mediated by a distinct UV-A specific photoreceptor, but not by phytochromes, UV-A/blue photoreceptors, or UV-B photoreceptors. Keywords: light response Direct comparisons were made between blue and dark, UV-A and dark, or UV-B and dark treatments. The dark control sample was labeled with Cy5 and the other samples were labeled with Cy3. In addition to these hybridizations, three concurrent split-control hybridizations of the dark control were made to correct gene specific dye-bias. Three biological replicates were made for each comparison. For each biological replicate, RNA was extracted from more than five plants.