Study On The Transcriptional Expression And The Promoter Function Of Key Genes Involved In Steroidal Glycoalkaloid Biosynthesis In Potato

Steroidal glycoalkaloids (SGAs) present in Solanum species are known for their toxic andproviding natural protection against pests. SGAs are closely associated with the eating qualityand processing quality of potato tubers. This study was to analyze the impact of genotypes, redlight illumination, and the duration of incubation on the SGAs biosynthesis at the transcriptionallevel. Wild species S. chacoense and the cultivated potato varieties Shepody, Favorita, Longshu3,and Zhangshu3were tested and their micro-tubers incubated at15oC with or without red lightillumination were used for real time quantitative PCR analysis. To further study the mechanismthat the red light-induced gene expression, we cloned the sgt3promoter. The GUS expressionvector driven by sgt3or CMV35S promoter was constructed and transformed to tobacco leavesfor functional analyzed.The main conclusions are as follows:1. The transcriptional level of seven genes involved in SGAs synthesis was higher inlight-sensitive varieties (Zhuangshu-3) when compared to the light-insensitivity varieties(Longshu-3), the result indicated that the genotype affected the SGAs synthesis.2. The red light induced the transcriptional expression of upstream gene (hmg1and hmg2) anddownstream gene (stg1and sgt3) involved in SGAs synthesis, but it inhibited branch gene(pvs1).3. The transcription start site of the sgt3promoter is located-152bp upstream of the translationstart site. We analyzed sequence of the promoter and predicted the core sequence, enhancer,repressor and a series of cis-elements, which involved in light regulation, pathogens, damage,drought and ABA hormone.4. The results demonstrated that the sgt3promoter can drive the expression of gus, but theexpression level was less than that drive by the CMV35S promoter. The highest gus expressionwas detected in tobacco leaves transformed by P572and P979, but gus expression was decreasedin P1312and P1870. We found more positive regulatory elements within the1000bp upstreamof translation start code.5. The tissue specificity analysis indicated that the sgt3driven GUS expression mainlyconcentrated in the veins of the tobacco leaves, but not detected in mesophyll cells. In the root,GUS was detected in meristem and vascular tissues. In tobacco stem, GUS was detected inepidermis, xylem and phloem as well.