Submitted to: Molecular Plant-Microbe Interactions
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/3/1996
Publication Date: N/A
Citation: Interpretive Summary: Plants respond to fungus diseases by producing antifungal substances that delay or stop development of the fungus pathogens. The plants do this by activating "defense" genes that set in motion metabolic processes that lead to production of the antifungal substances. However, the exact role or importance of individual defense genes is not understood. In our laboratory, we have isolated defense genes that cause the plant to produce an antifungal substance called thaumatin-like protein. The name "thaumatin" comes from a wild shrub in Africa where such substances were first found. We isolated the genes for thaumatin-like protein from oat plants infected by the stem rust fungus, which can cause severe oat disease in farmers' fields. We showed that the oat plants have four closely related genes for thaumatin-like proteins and that all are activated when the plant comes under attack by the stem rust fungus. This sets the stage for scientists in nour laboratory and elsewhere to add these genes to plants to improve their resistance to disease.
Technical Abstract: Four cDNA clones (corresponding to tlp-1, -2, -3 and -4 genes) encoding thaumatin-like (TL), pathogenesis-related proteins were isolated from oat (Avena sativa) infected by an incompatible isolate Pga-1H of the oat stem rust fungus (Puccinia graminis f.sp. avenae). All four cDNA clones contained an open reading frame predicted to encode a 169 amino acid polypeptide with a signal peptide of 21 amino acids at the N-terminus, suggesting that these proteins are transported through a secretory pathway. The amino acid sequences revealed high homology among the four cDNA clones. In plants infected with the incompatible isolate Pga-1H, or an inappropriate isolate Pgt-8D of P. graminis f.sp. tritici, high levels of tlp gene transcripts accumulated at 42-48 hr AI and thereafter when hypersensitive host cell death occurred and hyphal growth was inhibited. Spray with a light mineral oil used as a spore carrier induced transient expression of tlp-1, -2 and -3 genes at 16-30 hr AI which obscured the initial induction of the tlp genes in response to infection by the pathogens. In contrast, tlp-4 was induced very little by oil spray, so that induction was clearly observed in response to either compatible, incompatible, or inappropriate isolates at 24-30 hr AI. Wounding leaves by either slicing or puncturing them strongly induced tlp-1 and tlp-3, moderately induced tlp-2, but had no effect on tlp-4. The results showed that tlp genes displayed differential responses to oil spray, mechanical wounding and pathogen infection and that the expression of tlp genes, especially tlp-1, in oat is associated with resistance reactions in response to infection by incompatible and inappropriate isolates of the stem rust fungi.