Expression Of A Archaebacteria Glucoamylase In Transgenic Rice Seeds

α-amylase and glucoamylase are two key enzymes for starch hydrolysis for glucose production,α-amylase used for liquefaction is usually carried out at high temperature(95℃), while glucoamylase used for saccharification at a lower temperature(60℃). Thus the two enzymes are used separately in two steps with different reaction conditions. For this study we intended to produce a thermostable glucoamylase in rice, which may be used to hydrolyze starch simultaneously withα-amylase, which may resulted to simpler procedure for glucose production.A glucoamylase gene from a hyperthermophilic archaeon Sulfolobus solfataricus (SSG) (gi: 15897867) was reported with optimal temperature at 90℃and optimal pH of 5.5. This gene appears to be a good candidate to be used for one step starch hydrolysis. A rice codon optimized gene of SSG was synthesized. This SSG gene was constructed into T-DNA under the control a major rice seed storage protein Gt1 promoter, and transformed into rice by Agribacterium medicated transformation. Total of 26 transgenic lines were obtained. The PCR analysis suggested that all the transgenic line contain SSG gene. However, insignificant glucoamyalse activity was detected, indicating more transgenic lines need to be screened for higher glucoamylase activity.