A putative rhamnogalacturonan-II CMP-β-Kdo transferase identified using CRISPR/Cas9 gene edited callus to circumvent embryo lethality

Rhamnogalacturonan II (RG-II) is a structurally complex and conserved domain of the pectin present in the primary cell walls of vascular plants. Mutations that alter RG-II structure affect its crosslinking and are lethal or severely impair plant growth and development. Thus, few genes involved in RG-II synthesis have been identified. Here we developed a CRISPR/Cas9-mediated gene editing method to generate callus carrying loss-of-function mutations in the MPG2 gene that encodes a putative glycosyltransferase. Plants homozygous for this mutation do not survive. Our study of the callus mutant cell walls suggests that MGP2 encodes a CMP-β-Kdo transferase synthesizing RG-II sidechain C.