Functional Annotation and the Effect of Curing on the Expression of Skinning Injury Response Genes in Sweetpotato Cultivars

Skinning injury in sweetpotatoes (Ipomoea batatas) is responsible for significant postharvest loss resulting from storage diseases and weight loss. Unfortunately, there is no report on the genes involved in wound healing of sweetpotato and a better understanding will facilitate improved breeding strategies. An annealing control primer (ACP) system was used to identify genes  expressed after skinning injury of sweetpotato cultivar L07-146 storage roots. Using 20 ACPs, 63 differentially expressed genes (DEGs), 19 contigs were identified. Functional annotation of the 19 DEGs revealed that genes previously shown to respond to a(biotic) stress responses; genes involved in RNA, DNA related and gene expression; genes involved in cellular communication and signal transduction; and genes involved in metabolism, energy and cytoskeleton formation. Studies showed that genes involved lignin and suberin have been shown to hasten wound healing and curing has been shown to improve storability of root crops. We further analyzed the expression pattern of genes involved in lignin and suberin biosynthesis in response to skinning injury in cured (28 °C, RH 85%) and non-cured (ambient)  conditions in storage roots of a resistance (LA 10-70) and a susceptible (LA 07-146) cultivars of sweetpotato. The purpose was to study their transcript abundance in order to understand the tolerance to skinning injury mechanism associated with lignin and suberin formation in both cultivars. All skinning treatment were conducted on freshly harvested storage roots of both cultivars. This study revealed that these genes were regulated in opposite fashion in skinning resistant- and susceptible cultivars of sweetpotato with difference in timing of their induction under curing condition. These results also showed a clear evidence for a coordinated gene signaling cascade in pre- and lignin biosynthesis pathway. Taken together, this study demonstrated that major differences in skinning tolerance between these two cultivars were due to the ability of the skinning resistant cultivar to maintain highly regulated order in its transcript activity of genes involved in pre-lignin (TAL) and in lignin biosynthesis (PAL, CCOMT and CAD) and prevented early expression of Ext gene in response to skinning and in curing conditions.