DEHYDRATION-STRESS-REGULATED TRANSGENE EXPRESSION IN STABLY TRANSFORMED RICE PLANTS

To confer abscisic acid (ABA) and/or stress-inducible gene expression, an ABA-response complex (ABRC1) from the barley (Hordeum vulgare L.) HVA22 gene was fused to four different lengths of the 5' region from t he rice (Oryza sativa L.) Act1 gene. Transient assay of P-glucuronidas e (GUS) activity in barley aleurone cells shows that, coupled with ABR C1, the shortest minimal promoter (Act1-100P) gives both the greatest induction and the highest level of absolute activity following ABA tre atment. Two plasmids with one or four copies of ABRC1 combined with th e same Act1-100P and HVA22(I) of barley HVA22 were constructed and use d for stable expression of uidA in transgenic rice plants. Three South ern blot-positive lines with the correct hybridization pattern for eac h construct were obtained. Northern analysis indicated that uidA expre ssion is induced by ABA, water-deficit, and NaCl treatments. GUS activ ity assays in the transgenic plants confirmed that the induction of GU S activity varies from 3- to 8-fold with different treatments or in di fferent rice tissues, and that transgenic rice plants harboring four c opies of ABRC1 show 50% to 200% higher absolute GUS activity both befo re and after treatments than those with one copy of ABRC1.