Sweetpotato (Ipomoea batatas L.) is a globally important food crop susceptible to root-knot nematode (Meloidogyne incognita) infection, which causes significant crop losses. Previous transcriptome and proteome analyses have identified several genes that show differential expression patterns in susceptible and resistant cultivars in response to root-knot nematode (RKN) infection. Among the genes responsive to this process, sporamin (SPO) genes were identified as the most abundant in the transcriptome analysis, and additional changes in the expression of SPO genes that showed specific responses to RKN infection were identified during nematode infection. In this study, we used SPO genes used in previous studies to identify expression patterns under various abiotic stress conditions. The expression of four SPO genes in sweetpotato leaves was investigated under conditions of drought, high salt, and stress-related chemicals treatment. The expression of G13675/TU22356, G34367/TU56356, and G34382/TU56395 increased similarly under dehydration and chemicals treatment conditions. On the other hand, G34367/TU56358 was constantly expressed during the stress treated conditions. This study is expected to be used as basic data on how the gene for the major protein SPO of sweetpotato responds to various abiotic stress conditions as well as nematode infection.

Expression changes of stress-induced peroxidase (swpa2 and swpa4) and storage root-specific sporamin (spo-A and spo-B) genes were examined using qRT-PCR after treatment with wounding and bacterial pathogens on leaves of sweetpotato (Ipomoea batatas) plants. As a result of examining the expression change in the wounding treatment condition for 48 hours after treatment, which is a representative physical stress, the expression of all genes increased after 12 hours of wounding treatment, but the expression pattern of each gene group showed distinct differences thereafter. Expression levels of swpa2 and swpa4 strongly increased up to 36 or 48 hours after wounding treatment, whereas spo-A and spo-B expression levels strongly decreased after 24 or 36 hours after wounding treatment. Peroxidase and sporamin genes are involved in the early response after wounding treatment and, in particular, the peroxidase swpa2 and swpa4 genes are also involved in the late response after wounding treatment. Gene expression analysis after infection with P. chrysanthemi, which causes softness in sweetpotato, showed that the swpa2 and swpa4 genes were weakly induced after 8 hours and then strongly induced after 20 hours during pathogen infection. Expression of the spo-A gene was weakly induced in the pathogen-treated group after 20 hours, whereas spo-B showed an expression pattern similar to that of the peroxidase genes. The above results indicate that expression of the stress-induced peroxidase gene used in this study is induced not only by abiotic stress but also by biological stress caused by bacterial pathogen invasion and that peroxidase plays an important function in the initial defense response.