High-level production of health-beneficial glucoraphanin by multiplex editing of AOP2 gene family in mustard

Abstract

Intake of glucosinolates through the consumption of cruciferous vegetables has been associated with numerous health benefits. In recent decades, glucosinolate glucoraphanin has gained a lot of attention, as its hydrolysis product (sulforaphane) is known to possess numerous health-promoting benefits, including anti-cancer and chemopreventive activities. However, due to the low availability of glucoraphanin in most of the cultivated Brassica crops (except broccoli), there is an increasing interest in many laboratories around the world to manipulate the glucosinolate profile for human benefit. Here, we report the high-level production of health-beneficial glucoraphanin by CRISPR/Cas9 editing of the ALKENYL HYDROXALKYL PRODUCING 2 (BjuAOP2) gene family, displaying distinct expression profiles in the allotetraploid mustard, Brassica juncea. Multiplex editing of five BjuAOP2 homologues, using four gRNAs, provided glucoraphanin accumulation up to 41.60, 75.10, 59.21 and 27.64 μmoles/g dry weight in sprouts, microgreens, seeds and leaves, respectively, of the transgene-free BjuAOP2-edited lines, while providing a significant reduction of the anti-nutritional and goitrogenic alkenyl glucosinolates including progoitrin. The glucoraphanin enhancement in BjuAOP2-edited lines was found to be dose-dependent, wherein loss-of-function mutations in BjuAOP2.A09 and BjuAOP2.B01 homologues had a more prominent effect. The transgene-free BjuAOP2-edited lines were stable for high glucoraphanin and performed at par with the wild-type plants for various seed quality and yield parameters when tested under containment conditions in the field. The development of high-glucoraphanin mustard will help its adoption as a global superfood with health-promoting benefits and as a bioactive source of high-value sulforaphane for industrial production.