Abstract
Plant disease resistance governed by quantitative trait loci (QTL) is predicted to be effective against a broad spectrum of pathogens and long lasting. Use of these QTL to improve crop species, however, is hindered because the genes contributing to the trait are not known. Five disease resistance QTL that colocalized with defense response genes were accumulated by marker-aided selection to develop blast-resistant varieties. One advanced backcross line carrying the major-effect QTL on chromosome (chr) 8, which included a cluster of 12 germin-like protein (OsGLP) gene members, exhibited resistance to rice (Oryza sativa) blast disease over 14 cropping seasons. To determine if OsGLP members contribute to resistance and if the resistance was broad spectrum, a highly conserved portion of the OsGLP coding region was used as an RNA interference trigger to silence a few to all expressed chr 8 OsGLP family members. Challenge with two different fungal pathogens (causal agents of rice blast and sheath blight diseases) revealed that as more chr 8 OsGLP genes were suppressed, disease susceptibility of the plants increased. Of the 12 chr 8 OsGLPs, one clustered subfamily (OsGER4) contributed most to resistance. The similarities of sequence, gene organization, and roles in disease resistance of GLP family members in rice and other cereals, including barley (Hordeum vulgare) and wheat (Triticum aestivum), suggest that resistance contributed by the chr 8 OsGLP is a broad-spectrum, basal mechanism conserved among the Gramineae. Natural selection may have preserved a whole gene family to provide a stepwise, flexible defense response to pathogen invasion.
Highlights
Plant disease resistance governed by quantitative trait loci (QTL) is predicted to be effective against a broad spectrum of pathogens and long lasting
To establish a causal effect between defense response (DR) gene function and QTL, we have focused on a major-effect rice blast resistance QTL on rice chromosome 8 that colocalized with a barley (Hordeum vulgare) oxalate oxidase-like gene marker (HvOXOLP) in several rice mapping populations (Ramalingam et al, 2003; Liu et al, 2004)
Five QTL from cv Sanhuangzhan 2 (SHZ-2), including the major-effect chr 8 QTL that is associated with OsGLP genes, were introgressed into the susceptible commercial cv Texianzhan 13 (TXZ-13) using markerassisted selection, resulting in backcross line BC116 (Liu et al, 2004)
Summary
Plant disease resistance governed by quantitative trait loci (QTL) is predicted to be effective against a broad spectrum of pathogens and long lasting. The similarities of sequence, gene organization, and roles in disease resistance of GLP family members in rice and other cereals, including barley (Hordeum vulgare) and wheat (Triticum aestivum), suggest that resistance contributed by the chr 8 OsGLP is a broad-spectrum, basal mechanism conserved among the Gramineae. To establish a causal effect between DR gene function and QTL, we have focused on a major-effect rice blast resistance QTL on rice chromosome (chr) 8 (log of the odds 5 7.1–10; contributing over 30% of the phenotypic effect) that colocalized with a barley (Hordeum vulgare) oxalate oxidase-like gene marker (HvOXOLP) in several rice mapping populations (Ramalingam et al, 2003; Liu et al, 2004). Silencing of a Nicotiana GLP increased the performance of an herbivore (Lou and Baldwin, 2006)
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