Transcriptome-based dissection of starch synthesis-dependent characterization of Drumstick-forming on yield increase of Panax notoginseng taproots

Starch is the compound with the highest content in Panax notoginseng taproots, determining the taproot yield. Over 400 years of experience have revealed that Drumstick-forming characterizes the taproot yield increase, yet the increase connotation and its starch basis remain unclear. In this study, the weighing and drainage methods together with paraffin section and kit-based spectrophotometry indicted the Drumstick-forming characterized the extremely significant increases in the fresh weight (FW) per plant and starch granule density (SGD), the significant increases in the dry weight (DW), volume, amylose content (AC) and AC/amylopectin contents (APC) per plant, the significant decrease in the drying rate (DR) per plant and the non-significant increases in the APC, total starch content (TSC) and trehalose content (TC) per plant of the 2-year-old taproots, and the extremely significant increases in the FW, DW and volume per plant, the significant increase in the TC per plant, the extremely significant decrease in the SGD, the significant decrease in the AC, APC and TSC per plant and the non-significant decrease in the AC/APC and DR per plant of the 3-year-old taproots. Meanwhile, RNA-seq, phylogenetic analysis and quantitative real-time PCR showed that, due to the Drumstick-forming, the AC was mainly determined by the Pno04G003646 (phosphofructokinase gene, PFK), the APC mainly by the Pno09G001900 (invertase gene, INV) and Pno01G006431 (starch branching enzyme gene, SBE), the TSC mainly by the Pno01G006445 (fructose-bisphosphate aldolase gene, FBA), Pno01G006442 (FBA), Pno09G001900 (INV) and Pno01G006431 (SBE), and the AC, TSC and AC/APC were negatively regulated by the Pno06G005621 and Pno03G015691 both belonging to DNA binding with one finger. Altogether, this study clarifies the starch synthesis-dependent characterization of the Drumstick-forming on the increase of P. notoginseng taproot yields, underlying the optimization of the breeding and cultivation measures of P. notoginseng via inducing the Drumstick-forming.