No abstract

Magainins are a group of short peptides originally isolated from frog skin and thought to function as a natural defense mechanism against infection due to their antimicrobial properties. The engineered magainin analog peptide Myp30 was found to inhibit spore germination of the oomycete, Peronospora tabacina (Adam) in vitro, and the growth of a bacterial pathogen Erwinia carotovora subsp. carotovora (Jones). Transgenic tobacco (Nicotiana tabacum L.) plants expressing Myp30 were evaluated for resistance to these pathogens. The expression of the peptide only to an extracellular location resulted in significant reduction in sporulation and lesion size due to P. tabacina infection. A significant increase in resistance to the bacterial pathogen was also observed regardless of the targeting location of the peptide.

No abstract

Black shank [caused by Phytophthora parasitica (Dast.) var. nicotianae (B. de Haan) Tucker] is one of the most devastating diseases in tobacco (Nicotiana tabacum L.). Phytophthora parasitica var. nicotianae race 1 is the most damaging race of this fungus. The objective of this study was to identify the Nicotiana species that are resistant to P. parasitica var. nicotianae race 1 as part of the effort to develop Nicotiana‐based plant varieties for applications in the production of plant‐made pharmaceuticals (PMPs). The roots of approximately 26‐d‐old growth room–grown plants were inoculated with zoospores of an isolate of P. parasitica var. nicotianae race 1 by a dipping procedure. The percentage of plants that were free of symptoms 10 to 14 d after inoculation was taken as a measure of resistance to the fungus. We evaluated a total of 97 Nicotiana accessions from 37 species from the USDA collection and other sources. Among the 97 accessions, three from N. debneyi Domin, two from N. repanda Willd. ex Lehm., and one each from N. megalosiphon Van Heurck & Mull. Arg., N. plumbaginifolia Viv., N. suaveolens Lehm., and N. sylvestris Speg. & Comes were found to be resistant. Their resistances were further confirmed after they were evaluated for an additional three times. These nine accessions were then challenged by another isolate of race 1. All accessions except for the N. sylvestris accession were found to be resistant. Nicotiana debneyi, N. megalosiphon, and N. suaveolens were not previously reported to be resistant to P. parasitica var. nicotianae race 1. Our study indicated that the undomesticated Nicotiana species constitute a rich genetic source for resistance to the tobacco disease black shank.

It has been reported that the expression of the yeast poly(A) binding protein gene (PAB1) in plants leads to an induction of disease resistance responses, accompanied by alterations in the growth habit of the plant (Li et al. Plant Mol. Biol. (2000) 42 335). To capitalize on this observation, a feedback-regulated PAB1 gene was assembled and introduced into tobacco and Arabidopsis. The regulation entailed the linking of the expression of the PAB1 gene to control by the lac repressor, and by linking lac repressor expression to the disease resistance state of the plant, such that the induction of systemic defense responses by accumulation of the yeast poly(A) binding protein would turn off the expression of the PAB1 gene. Plants containing this system showed elevated and/or constitutive expression of disease-associated genes and significant resistance to otherwise pathogenic organisms. As well, they displayed a nearly normal growth habit under laboratory and greenhouse settings. These studies indicate that the expression of cytotoxic genes (such as the PAB1 gene) in plants can be controlled so that enhanced disease resistance can be achieved without significantly affecting plant growth and development.