Transient expression of reporter proteins can alter plant gene expression

To determine whether expression of commonly used reporter genes can alter plant gene expression we used the RNA fingerprinting technique, cDNA-AFLP analysis. We analysed changes in gene expression in response to transient expression (agro-infiltration) of two derivatives of the green fluorescent protein (GFP) reporter gene. Sixty plant cDNA-AFLP fragments showed altered expression profiles in response to an endoplasmic reticulum (ER)-targeted GFP (GFP5) when compared with a non-targeted form (GFP4) or to controls. Two plant genes showed altered expression profiles in response to GFP4. One plant gene showed an altered expression profile in response to both GFP4 and GFP5. No changes in gene expression were observed in response to the widely used beta-glucuronidase (GUS) reporter gene. However, altered expression profiles were observed when GUS was targeted to the ER (Cht-GUS) suggesting that reporter proteins can alter plant gene expression especially when ER-targeted. The GFP5-induced genes were also up-regulated in transgenic plants constitutively expressing a GFP5 transgene but only after agro-inoculation of these plants with GFP5. Many of the induced genes showed homology to genes involved in plant defence, suggesting that the plant response to ER-targeted reporter proteins can mimic the response to attack by pathogens. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.