Transcript profiling of two potato cultivars during glycoalkaloid-inducing treatments shows differential expression of genes in sterol and glycoalkaloid metabolism

Abstract

Steroidal glycoalkaloids (SGA) are sterol-derived neurotoxic defence substances present in several members of the Solanaceae. In the potato (Solanum tuberosum), high SGA levels may render tubers harmful for consumption. Tuber SGA levels depend on genetic factors, and can increase as a response to certain stresses and environmental conditions. To identify genes underlying the cultivar variation in tuber SGA levels, we investigated two potato cultivars differing in their SGA accumulation during wounding or light exposure; two known SGA-inducing treatments. Using microarray analysis coupled to sterol and SGA quantifications, we identified a small number of differentially expressed genes that were associated with increased SGA levels. Two of these genes, encoding distinct types of sterol Δ24-reductases, were by sense/antisense expression in transgenic potato plants shown to have differing roles in sterol and SGA metabolism. The results show that an increased SGA level in potato tubers during both wounding and light exposure is mediated by coordinated expression of a set of key genes in isoprenoid and steroid metabolism, and suggest that differences in this expression underlie cultivar variations in SGA levels. These results may find use within potato breeding and quality assessment.

Light exposure and wounding: synergistic effects on steroidal glycoalkaloid accumulation in potato tubers during storage

“…Studies have found that the SGA content of potato tubers varies with time (Percival, ; Dao & Friedman, ). The SGA content in the tubers exposed to light for 96 h was clearly higher than that of control tubers kept in the dark (Nahar et al ., ). However, these studies did not monitor the SGA content in tuber skin or flesh after treatment.…”

“…Therefore, it is very important to reduce the extent of wounding in potato tubers. In addition, it is reported that the activity of the relative enzyme of SGA in potato tubers increased slowly before 11 h and reaches a maximum after 16 h (BergenstrÅhle et al ., ), and the expression of related SGA synthesis genes increased after potato injury (Nahar et al ., ). Therefore, wound could activate the related synthetic genes of SGA in potato, which leads to the increase of SGA content.…”

“…1b, d). Relevant studies have found that light can increase the chlorophyll content in potato tubers (Dao & Friedman, 1994), which caused the tubers to turn green (Mfb et al, 1993;Nahar et al, 2017). Therefore, the most likely reason for this is that potato tubers can produce chlorophyll under light conditions.…”

“…Therefore, wound could activate the related synthetic genes of SGA in potato, which leads to the increase of SGA content. Although several researchers have investigated the effects of light exposure and wounding on potato SGA and have described the underlying genetic molecular mechanism (Nahar et al, 2017), evidence for the synergistic effects of light and wounding on potato tubes in storage is still lacking. We found that the SGA content of the flesh of potato tubers under the light conditions was significantly higher than that under the dark conditions.…”

“…Past studies have revealed that the SGA content in potato tubers is increased during wounding (Nahar et al ., ). Our previous preliminary experiment indicated that SGA content was higher in the skin than in the flesh and increased significantly with time in the skin but not in the flesh.…”