Genome-wide analysis of polyphenol oxidase gene family in Solanum tuberosum and functional identification of StuPPO9 in regulating tolerance to Phytophthora infestans

Abstract

Polyphenol oxidase (PPO) is the key enzyme involved in the enzymatic browning of potato tubers. However, the understanding of its other functions, as well as the underlying molecular mechanisms, is still limited. StuPPO9 was predicted as an inducible gene in response to disease defense and cell rescue, as analyzed using the EST database. In this study, an identification and evolutionary analysis of PPOs in Solanum tuberosum was conducted. A total of 10 members of StuPPOs were identified and their gene structure, protein motifs, chromosomal location, and tissue distribution were further investigated. QRT-PCR analysis indicated that most PPOs were induced or inhibited under hormone treatments, and StuPPO9 showed the highest expression level when induced by Phytophthora infestans. Therefore, StuPPO9, the only one located on chromosome 2, was selected for further study. The StuPPO9 overexpressing Nicotiana benthamiana transgenic line effectively slowed down the growth of P. infestans and showed more tolerance compared to the wild type (WT). Moreover, the molecular markers NtHin1 and PR genes were significantly upregulated in the transgenic tobacco than in WT under P. infestans infection. This study will provide a basis and reference for future research on the roles of StuPPO9 in disease defense.