Overexpression of IbLfp in sweetpotato enhances the low-temperature storage ability of tuberous roots.

Sweetpotato (Ipomoea batatas [L.] Lam) is a prospective food crop that ensures food and nutrition security under the dynamic changes in global climate. Peroxidase (POD) is a multifunctional enzyme involved in diverse plant physiological processes, including stress tolerance and cell wall lignification. Although various POD genes were cloned and functionally characterized in sweetpotato, the role of POD in lignification and low-temperature storage ability of sweetpotato tuberous roots is yet to be investigated. In this study, we isolated the cold-induced lignin forming peroxidase (IbLfp) gene of sweetpotato, and analyzed its physiological functions. IbLfp showed more predominant expression in fibrous roots than in other tissues. Moreover, IbLfp expression was up-regulated in leaves and roots under cold stress, and was altered by other abiotic stresses. Tuberous roots of transgenic sweetpotato lines overexpressing IbLfp (LP lines) showed improved tolerance to low temperature, with lower malondialdehyde and hydrogen peroxide contents than non-transgenic sweetpotato plants under cold stress. The enhanced cold tolerance of LP lines could be attributed to the increased basal activity of POD, which is involved in reactive oxygen species (ROS) scavenging. Moreover, greater accumulation of lignin could also contribute to the enhanced cold tolerance of LP lines, as lignin acts as a protective barrier against invading pathogens, which is a secondary symptom of chilling injury in sweetpotato. Overall, the results of this study enhance our understanding of the function of POD in low-temperature storage of sweetpotato tuberous roots.