Functional analysis of the promoter of the rice sucrose phosphate synthase gene (sps1)

Sucrose phosphate synthase (SPS) is a key enzyme in the translocation of photoassimilates from sink-to-source tissues and the remobilization of reserves from storage tissues during seed germination. The tissue specific distribution of SPS is mainly determined by transcriptional mechanisms. To gain further insight into the mechanisms that regulate the transcriptional activity of SPS genes, we carried out a deletion analysis of the rice sps1 promoter using transient expression assays and transgenic rice plants. The sps1 promoter is atypical since it lacks recognizable TATA and initiator sequences near the transcription start site. It was found that the minimal active sps1 promoter consists of a 146bp 5′ flanking sequence that is capable of directing activity in photosynthetic tissues in rice. No positive or negative regulatory elements upstream to position -146 influencing expression in photosynthetic tissues were found. It was also observed that the sps1 promoter fragment containing 5′ sequences upstream to position -1830 conferred expression only in the scutellum of germinating seeds, whereas shorter promoter versions directed expression in the scutellum but also in the aleurone layer, suggesting the presence of a negative element upstream of position -1188 that suppresses expression in the aleurone. Gain of function experiments suggest that the negative element present upstream of position -1188 is necessary but not sufficient to suppress expression in the aleurone.