CRISPR/Cas-mediated polyphenol oxidase gene knockout in potato reveals divergent roles in resistance to bacterial wilt and late blight

Abstract

Polyphenol oxidases (PPOs) play a pivotal role in plant immune responses by catalysing the oxidation of phenolic compounds into cytotoxic quinones and melanin and contributing to the fortification of cell walls. Despite their biological significance, the high expression of PPOs in potatoes is not desirable due to their promotion of tuber browning. This study elucidates the relationship between PPO activity and defense mechanisms against the diverse pathogens Ralstonia solanacearum (Rs) and Phytophthora infestans (Pi) while mitigating enzymatic browning. CRISPR/Cas-mediated editing of the tuber-and root-specific PPO genes in the 'Desiree' and 'Balatoni Rozsa' potato cultivars considerably reduced enzymatic activity and browning. Among four PPO-edited mutant lines, three exhibited increased susceptibility to Rs while responses to Pi remained unchanged, underscoring the importance of PPOs in resistance to Rs. The PPO knockouts resulted in significant shifts in metabolite and hormone profiles characterized by elevated levels of dihydrokaempferol, coniferyl alcohol and taxifolin among other metabolites in the roots of Rs-susceptible mutants. Additionally, reduced PPO activity in these lines correlated with increased concentrations of salicylic acid, jasmonic acid and several antimicrobial compounds and alterations in flavonoid regulation. These findings highlight the complex role of PPOs in plant defense, establishing a positive correlation between PPO activity and resistance to Rs, while offering insights into the trade-offs associated with PPO gene editing in potatoes.