Nucleotide sequence of a pathogenesis-related gene of potato

Abstract

Environmental stresses cause rapid and specific changes in plant metabolism. Among the various metabolic activities stimulated in potato during the defense response are that of enzymes required for phytoalexin synthesis [2], chitinases and 1,3-fl-glucanases [7], as well as phenylalanine ammonia-lyase and 4-coumarate CoA-ligase [3, 5]. Treatment of potato tuber disks with arachidonic or eicosapentaenoic acid elicits the accumulation of several mRNAs [8]. cDNA clones corresponding to two of these mRNAs (pSTH-2 and pSTH-21) were isolated and characterized [9]. They were found to accumulate in tubers upon wounding and elicitor treatments. pSTH-2 related mRNAs also accumulate in stems upon wounding and in potato and tomato leaves treated with a mycelial homogenate from the late blight fungus Phytophthora infestans [9]. Proteins encoded by these cDNAs (pSTH-2 and pSTH-21) were found to be highly similar to pea pathogenesis-related (PR) protein pi49 and pI 176 [4], to parsley PR protein PRI-1 and PR1-3 [ 10], and to Betvl, the major pollen allergen from white birch [ 1]. The two potato cDNA clones were used to screen a genomic library made in the vector 2 EMBL 3. One hybridizing clone was characterized and shown to contain a gene corresponding to pSTH-21. Its nucleotide sequence is presented in Fig. 1. The gene is made of two exons that are 100~o identical to the pSTH-21 cDNA clone, including the 5' and 3' untranslated regions [9]. The intervening sequence is 347 bp long and interrupts the coding region at amino acid 57. As in the case for many plant genes, no AAUAAA consensus polyadenylation signal sequence can be found in the vicinity of the poly(A) addition site [6]. Multiple transcription start sites have been identified by reverse transcription of polyadenylated RNA from elicitortreated tuber disks, using as a primer a synthetic oligonucleotide complementary to nucleotides 957 to 971. The fact that STH-21 is part of a multigene family [8, 9] could explain this result. Sequences homologous to TATA and CAAT boxes are located at position 22 (TATAAATA) and 117 (CAAAT), respectively, from the most upstream transcription start site. Identical sequences are also located 27 and 67/102bp upstream of the transcription start site of the parsley PRI-1 gene [10].