Molecular breeding of SGA-free potatoes accumulating pharmaceutically useful saponins

Abstract

Steroidal glycoalkaloids （SGAs） are toxic specialized metabolites that are found in Solanaceae.　Potato （Solanum tuberosum） contains the SGAs α-solanine and α-chaconine, which are biosynthesized from cholesterol.　Several biosynthetic genes including SSR2 and two cytochrome P450 genes （CYP72A188 and CYP72A208） have been identified, and the transgenic potato plants silencing these biosynthetic genes showed SGA-reduced phenotypes.　Here we summarize our recent results and strategy towards metabolic engineering of potato accumulating pharmaceutically useful compounds by genome editing.　CYP88B1, which is involved in a later step of the SGA biosynthetic pathway with unknown catalytic function, is co-ordinately expressed with the SGA biosynthetic genes.　We applied CRISPR/Cas9 system to knockout potato CYP88B1.　The CYP88B1-knockout potatoes showed no accumulation of SGAs, and furthermore the corresponding amounts of steroidal saponins were accumulated in the knockout potatoes.