Estrogen-inducible GFP expression patterns in rice (Oryza sativa L.)

We investigated estrogen-inducible green fluorescent protein (GFP) expression patterns using an estrogen receptor fused chimeric transcription activator, XVE, in the monocotyledonous model plant rice (Oryza sativa L.). This system has been shown to be an effective chemical-inducible gene expression system in Arabidopsis and has been applied to other plants in order to investigate gene functions or produce marker-free transgenic plants. However, limited information is available on the correlation between inducer concentration and the expression level of the gene induced in monocots. Here, we produced a transgenic rice integrated estrogen-inducible GFP expression vector, pLex:GFP, and investigated dose-response and time-course patterns of GFP induction in rice calli and seedlings for the first time. With 17-β-estradiol treatment at >5 μM, GFP signals were detected in the entire surface of calli within 2 days of culture. Highest GFP signals were extended for 8 days with estradiol treatment at 25 μM. In three-leaf-stage seedlings, GFP signals in the leaves of pLex:GFP-integrated transgenic lines were weaker than those in the leaves of p35S:GFP-integrated transgenic lines. However, GFP signals in the roots of pLex:GFP- and p35S:GFP-integrated transgenic lines were similar with estradiol treatment at >10 μM. With regard to controlling appropriate gene expression, these results might provide helpful indications on estradiol treatment conditions to be used for the XVE system in rice and other monocots.