Characterization of Two Virus-Inducible Plant Promoters

Abstract

The hypersensitive response of plants to infection with pathogens is accompanied by the induction of host genes encoding a diversity of proteins such as enzymes from the phenylpropanoid patway, peroxidases, hydrolytic enzymes, proteinase inhibitors, etcetera (for references see Bol and Van Kan 1988, Collinge and Slusarenko 1987). Studies on the induction of host proteins by virus infection were initiated by Van Loon and Van Kammen (1970) and Gianinazzi et al (1970) in the early seventies. Their model system consisted of tobacco plants reacting hypersensitively to infection with tobacco mosaic virus (TMV). The induction of at least 10 acidic proteins was observed which are all excreted by the plant cells into the intercellular space of the leave (see Bol and Van Kan 1988). These were named “pathogenesis- related” (PR) proteins 1a, 1b, 1c, 2, N, O, P, Q, R and S. Proteins 1a, 1b and 1c (15 kDa) have a highly homologous amino acid sequence; their function is not known (Cornelissen et al. 1987). Proteins 2, N and 0 (40 kDa) and proteins P and Q (29 kDa) were shown to be β-1,3-glucanases and chitinases, respectively (Kauffmann et al. 1987, Legrand et al. 1987). The function of protein R (13–15 kDa) is not known. Protein S (23 kDa) is homologous to the sweet-tasting protein thaumatin and to a maize protein that inhibits enzymes in the digestive tract of insects (Cornelissen et al 1986, Pierpoint et al 1987, Richardson et al 1987). It has been speculated that the hydrolytic enzymes (PR proteins 2, N, O, P and Q) play a role in the TMV-induced resistance of tobacco to fungal infection while PR-S could be involved in an induced resistance to insect attack (see Bol and Van Kan 1988).