Pathogen‐Defence Gene prp1–1 from Potato Encodes an Auxin‐Responsive Glutathione S‐Transferase

Abstract

Genetic studies have previously implicated the prp1 gene family in the defence of potato against infection with the late blight fungus Phytophthora infestans. Here, we show that the concentrations of PRP1 mRNA as well as protein rapidly increase in potato leaves after fungal infection and stay at high levels during an extended period of the infection cycle. After separation of subcellular components by differential centrifugation, PRP1 protein was identified in the cytosolic fraction. Expression studies with chimeric promoter/β‐glucuronidase gene constructs in transgenic potato plants provided evidence that transcription of the prp1‐1 gene, representing one member of the prp1 gene family, is at least partly responsible for the accumulation of PRP1 mRNA and protein upon fungal infection. After expression of the prp1‐1 coding sequence in Escherichia coli, the corresponding 26–kDa protein exhibited glutathione S‐transferase activity with Km values of 9.8 mM and 0.11 mM for the artificial standard substrate 1‐chloro‐2,4–dinitrobenzene and glutathione, respectively. Photoaffinity labeling of the protein with tritiated 5–azido‐indole‐3–acetic acid suggested that the phytohormone indole‐3–acetic acid or a structurally related compound serve as a regulator or substrate of the prp1‐1 encoded glutathione S–transferase. This assumption was further supported by the inhibitory effect of the phytohormone on the enzyme activity in vitro. The implications of these findings for a potential involvement of indole‐3–acetic acid in the control of defence reactions are discussed.

Resistance gene-dependent plant defense responses.

“…Furthermore, increased transcription of specific SOD and catalase genes may occur to ensure that maximal enzymatic activity is maintained within the appropriate cellular compartments (Bowler et al, 1994). For example, the expression of glutathione peroxidase, glutathione S-transferase, and polyubiquitin genes has been detected in incompatible interactions (Mauch and Dudler, 1993;Hahn and Strittmatter, 1994;Levine et al, 1994). Glutathione peroxidase activity can block cell death in mammalian systems (Hockenbery et al, 1993), whereas glutathione S-transferase detoxifies the products of lipid membrane peroxidation and other products of cellular oxidative stress (Berhane et al, 1994).…”

Engineering disease resistance in plants

“…These include the parsley Pr-1 genes (Rushton et al, 1996), the potato Gst1 (a glutathione Stransferase; Hahn and Strittmatter, 1994) and Sth-2 genes (Pr-10-like; Matton et al, 1993), the grapevine Vst1 gene involved in phytoalexin biosynthesis (Schubert et al, 1997), the asparagus . In the Arabidopsis Pr-1 promoter a W-box like sequence was identified that seemed to be involved in negative regulation of inducible expression .…”

PcMYB1, a novel plant protein containing a DNA‐binding domain with one MYB repeat, interacts in vivo with a light‐regulatory promoter unit

“…The ORFs were constructed into the vector pQE60 (Qiagen, Hilden) for expression in E. coil, and into pBSexp (da Costa e Silva et aL, 1993) for expression by coupled in vitro transcription/ translation. The constructs expressing GST and rMYB305 were kindly provided by G. Strittmatter and C. Martin, respectively (Hahn and Strittmatter, 1994;Jackson et aL, 1991). All plasmid constructions were verified by sequencing.…”