EFFECT OF ATP SULFURYLASE OVEREXPRESSION IN BRIGHT-YELLOW-2 TOBACCO CELLS - REGULATION OF ATP SULFURYLASE AND SO42- TRANSPORT ACTIVITIES

To determine if the ATP sulfurylase reaction is a regulatory step for the SO42--assimilation pathway in plants, an Arabidopsis thaliana ATP sulfurylase cDNA, APS2, was fused to the 35S promoter of the cauliflow er mosaic virus and introduced by Agrobacterium tumefaciens-mediated t ransformation into isolated Bright Yellow 2 tobacco (Nicotiana tabacum ) cells. The ATP sulfurylase activity in transgenic cells was 8-fold t hat in control cells, and was correlated with the expression of a spec ific polypeptide revealed by western analysis using an anti-ATP sulfur ylase antibody. The molecular mass of this polypeptide agreed with tha t for the overexpressed mature protein. ATP sulfurylase overexpression had no effect on [S-35]SO42- influx or ATP sulfurylase activity regul ation by S availability, except that ATP sulfurylase activity Variatio ns in response to S starvation in transgenic cells were 8 times higher than in the wild type. There were also no differences in cell growth or sensitivity to SeO42- (a toxic SO42- analog) between transgenic and wild-type cells. We propose that in Bright Yellow 2 tobacco cells, th e ATP sulfurylase derepression by S deficiency may involve a posttrans criptional mechanism, and that the ATP sulfurylase abundance is not li miting for cell metabolism.