Equipping potato with resistance against pathogens by the use of CRISPR/Cas genome editing

Potato is a staple crop worldwide, but its cultivation is threatened by diseases like bacterial wilt caused by Ralstonia solanacearum and late blight as result of Phytophthora infestans infection. The outcome of these infections may depend on the presence or absence of plant resistance factors (physical barriers, recognition receptors, stress hormones, production of antimicrobial compounds and pathogenesis related proteins, etc.) and susceptibility factors (interaction partners of plant-injected bacterial proteins, plant genes feeding the pathogen like sugar transporters, and plant negative immunoregulators). Here, we targeted various potato genes for CRISPR/Cas genome editing in order to improve the metabolic and immunological response of potato plants, thereby giving them an edge over these highly effective pathogens. The knockout of polyphenol oxidase (PPO) genes caused widespread metabolic and hormonal changes (e.g., increased scopoletin, taxifolin, salicylic acid, and jasmonic acid production) but still compromised the resistance against Ralstonia solanacearum, underlining the importance of PPO activity as a resistance mechanism. Meanwhile the knockout of the salicylic acid-degrading downy mildew resistance 6 enzyme increased potato resistance against bacterial wilt. We also attempted to boost the immune system by knocking out the microRNA gene miR396. The miR396 knock-out plants showed a delay in bacterial wilt symptoms, but they were more sensitive to late blight. Our studies show successful application of the CRISPR/Cas system for gene function studies. Strong plant resistance may be achieved by the combination of successful single-gene strategies.