Chloroplast-dependent and light-independent expression of the tobacco rbcS promoter–GUS chimeric gene in black spruce

Abstract

The tobacco rbcS (ribulose bisphosphate carboxylase small subunit) promoter, fused to the β-glucuronidase (GUS) reporter gene, was delivered to black spruce (Piceamariana (Mill.) BSP) tissues via microprojectile DNA bombardment, and its regulation was studied. The expression of the tobacco rbcS promoter–GUS chimeric gene was dependent on the presence of chloroplasts in black spruce tissues, as demonstrated in two ways: (i) there was no GUS activity expressed in zygotic embryos where no chloroplasts were observed, whereas it was expressed in light- and dark-grown seedlings that contained mature or immature chloroplasts; (ii) a herbicide, Norflurazon, destroyed chloroplast structure in seedlings and inhibited the expression of the tobacco rbcS promoter–GUS chimeric gene. A control chimeric gene, the cauliflower mosaic virus (CaMV) 35S promoter–GUS fusion gene was not inhibited by Norflurazon. Unlike in angiosperms, light had no effect on the expression of tobacco rbcS promoter–GUS chimeric gene. Both light- and dark-grown seedlings showed GUS activity, and expression in dark-grown seedlings was not enhanced by light. These results suggest that the tissue-specific regulation of the rbcS promoter may be conserved between angiosperms and conifers, but that the light regulation of this promoter may not be conserved.