Transcriptome and physiological analysis revealed the difference of resistance to fresh-cut browning among sweetpotato genotypes

Sweetpotato [Ipomoea batatas (L.) Lam.] storage roots tend to become brown due to damage incurred during harvest, transportation, processing and storage. Understanding the mechanism of sweetpotato browning is of great significance for breeding varieties with low browning, which have greater economic value. In this study, after analysis of the Browning Degree (BD) of 76 sweetpotato genotypes and analyzing the correlations between BD, the activities and contents of phenylalanine ammonia-lyase (PAL), peroxidase (POD) and polyphenol oxidase (PPO) for 21 genotypes, two genotypes, S07 (browning-resistant) and S28 (easily browned), were selected to elucidate the differences in the browning mechanism after fresh-cutting by physiological and transcriptome analyses. Genotype S28 had higher PAL, POD and PPO activities and a higher phenolic content after fresh-cutting compared with the basal level and genotype S07. Cell compartmentalization was severely damaged in fresh-cut S28. An RNA-Seq analysis showed that the phenylpropanoid biosynthesis in S28 was more active and gene families of related enzymes were more actively expressed. In conclusion, sweetpotato browning is due to a high content of phenolic compounds, and the high activity of PPO and POD resulting from the up-regulation of related genes. This study provided high quality breeding materials and a relevant theoretical basis for breeding browning-resistant sweetpotato varieties.