Nucleotide sequence of a cDNA clone encoding a thaumatin-like protein from Arabidopsis.

SAR in plants is found to correlate with induction of a set of putative defense genes including PR proteins (Linthorst, 1991). The PR proteins are a group of extracellular proteins that are induced by different phytopathogens such as viruses, bacteria, and fungi, and SAR-inducing compounds such as salicylic acid and 2,6-dichloroisonicotinic acid (Bol et al., 1990; Uknes et al., 1992). These proteins have been extensively studied in tobacco (Nicotiana tabacum) and are detected in many plant species in both dicotyledonous and monocotyledonous plants (Bol et al., 1990; Linthorst, 1991). One group of PR proteins (PR-5) is designated as thaumatin-like proteins based on the proteins’ extensive homology with thaumatin, a sweet-tasting protein from Thaumatococcus daniellii (Cornelissen et al., 1986; Pierpoint et al., 1990). Recently, SAR has been demonstrated in Arabidopsis and this resistance was correlated with induction of PR proteins including a thaumatin-like protein (Uknes et al., 1992). The thaumatin-like proteins purified from different plant systems have been shown to inhibit the growth of fungal pathogens in vitro (Vigers et al., 1991; Woloshuk et al., 1991). We are interested in constitutively expressing thaumatin-like proteins in transgenic plants to study their role in disease resistance against fungal pathogens. Here we report the sequence of a cDNA for thaumatin-like protein from Arabidopsis, which is different from previously reported thaumatin-like protein from the same system (Table I). A floral meristem cDNA library constructed in AZAP I1 vector was screened with a partial cDNA for thaumatinlike protein. Two of the isolated cDNA clones (ATLP-1 and ATLP-2) were sequenced. The ATLP-1 is 1039 nucleotides long with an open reading frame starting at nucleotide 41 and ending at nucleotide position 772. The deduced polypeptide is 243 amino acids long and contains a putative signal peptide at the amino-terminal end. The nucleotide sequence of ATLP-1 cDNA showed limited nucleotide sequence similarity with other thaumatin-like proteins from plants including Arabidopsis. The predicted amino acid sequence of ATLP-1 is 52% identical to previously reported thaumatin-like protein (PR-5) from Arabi-