Synthetic tetramer of a Phytophthora sojae-inducible fragment from soybean GmaSKTI36 promoter improves its pathogen induction activities

• The soybean GmaSKTI36 gene is strongly induced upon Phytophthora sojae infection.
• Its promoter could mediate immediate and early gene expression.
• A critical 122 bp fragment was identified in this promoter.
• A synthetic promoter by tetramerizing this fragment can improve its induction activities.

Using pathogen-induced promoters to control expression of the functional genes in transgenic plants may greatly increase the chances of boosting disease resistance. However, the number of the inducible promoters is limited. Here, we found that soybean GmaSKTI36 gene is strongly induced upon Phytophthora sojae infection. Functional analysis showed that its promoter could mediate rapid and strong induction of GUS expression upon pathogen infection in both Nicotiana benthamiana leaves and soybean hairy roots. Then, a 122 bp fragment that was critical to the activity was successfully identified by a progressive 5′ deletion analysis. Importantly, we found that a synthetic promoter by tetramerizing this fragment could confer strong P. sojae induction activities. Overall, the results suggested that the GmaSKTI36 promoter, the 122 bp fragment, and the synthetic promoter are potentially useful pathogen-inducible promoters.