Growth kinetics, metabolite yield, and expression analysis of biosynthetic pathway genes in friable callus cell lines of Rhodiola imbricata (Edgew)

Abstract

The plant cell culture provides an efficient technique for growth and production kinetics studies of bioactive compounds present in plants. Therefore, the present study investigated, for the first time, to identify the specific culture days required for higher metabolite yield in Rhodiola imbricata. A transcript-level gene expression study was conducted to understand the molecular cues associated with metabolite biosynthesis. The leaf callus cell line showed an optimum growth rate (FW: 20 g/100 mL, DW: 1.21 g/100 mL), growth index (19.00), salidroside (3.68 mg/g DW, rosavin (0.21 mg/g DW and rosarin (0.08 mg/g DW) on 24th day of the incubation period. However, salidroside, rosavin, and rosarin metabolite yield followed the growth-dependent manner in both callus cell lines, while tyrosol and p-coumaric acid showed growth independent accumulation pattern. Moreover, the antioxidant study displayed maximum phenolic content (8.07 mg/g DW) on day 18, flavonoid content (9.73 mg/g DW) on day 3, and DPPH activity (IC50; 0.79 mg/mL) on day 24 in leaf callus cell line. The RT-qPCR analysis showed upregulation of PAL, 4-HPAAS, 4-HPAAR, and UDPGT genes associated with metabolite accumulation. Expression analysis revealed a positive correlation with the metabolites yield. Furthermore, the optimized parameter could be exploited for a higher yield of specific metabolite and sequential scale-up studies. This is the first-ever study on the specific growth phase and accumulation pattern of metabolites in the friable callus cell lines of Rhodiola imbricata. Similarly, molecular signatures were also investigated to elucidate key genes associated with salidroside and rosavins biosynthesis. Furthermore, current optimized parameters lay the foundation for a cell suspension study, scale-up, and year-round metabolite production.