A novel thaumatin-like protein gene of tobacco is specifically expressed in the transmitting tissue of stigma and style

Abstract

 A cDNA clone that encodes a novel thaumatin-like glycosylated protein, SE39b, which constitutes one of the major proteins of the stigmatic exudate of tobacco, was isolated and sequenced. The deduced amino acid sequence of SE39b shows 37% identity with the pathogenesis-related protein of tobacco, PR-R1, and 52% identity with the thaumatin-like protein (TLP) of Arabidopsis. All 16 cysteine residues are conserved in SE39b as they are in all TLPs. Three potential glycosylation sites found in SE39b were consistent with a previous finding that concanavalin A has an affinity for SE39b. Northern blot and in situ analyses demonstrated that the gene was specifically expressed in the transmitting tissue of the stigma and style, and the transcript amounts reached maximum levels at anthesis. mRNA from orthologs of the gene of SE39b was detected in species of Cestreae, but not in species of Solaneae. SE39b should be categorized as a PR-like glycoprotein which is developmentally regulated and specifically expressed in the transmitting tissue of the stigma and style, such as Sp41 [(1,3)-β-glucanase], SK2 and Chi2;1 (chitinase).