Abstract
BackgroundHigher plants possess a large multigene family encoding secreted class III peroxidase (Prx) proteins. Peroxidases appear to be associated with plant disease resistance based on observations of induction during disease challenge and the presence or absence of isozymes in resistant vs susceptible varieties. Despite these associations, there is no evidence that allelic variation of peroxidases directly determines levels of disease resistance.Methodology/Principal FindingsThe current study introduces a new strategy called Prx-Profiling. We showed that with this strategy a large number of peroxidase genes can be mapped on the barley genome. In order to obtain an estimate of the total number of Prx clusters we followed a re-sampling procedure, which indicated that the barley genome contains about 40 peroxidase gene clusters. We examined the association between the Prxs mapped and the QTLs for resistance of barley to homologous and heterologous rusts, and to the barley powdery mildew fungus. We report that 61% of the QTLs for partial resistance to P. hordei, 61% of the QTLs for resistance to B. graminis and 47% of the QTLs for non-host resistance to other Puccinia species co-localize with Prx based markers.Conclusions/SignificanceWe conclude that Prx-Profiling was effective in finding the genetic location of Prx genes on the barley genome. The finding that QTLs for basal resistance to rusts and powdery mildew fungi tend to co-locate with Prx clusters provides a base for exploring the functional role of Prx-related genes in determining natural differences in levels of basal resistance.
Highlights
Class III plant peroxidases (EC 1.11.1.7; Prxs) are enzymes that catalyze oxidoreduction between H2O2 and various reductants and are involved in a broad range of physiological processes, including plant defense [1]
In earlier studies we identified six Prx genes to map within 1cM from markers associated with several quantitative trait loci (QTLs) contributing to basal resistance to barley leaf rust (Puccinia hordei Otth; [13]) and non-host resistance to several unadapted rust fungi [14]
Others have shown that the barley HvPrx7 peroxidase mRNA accumulates in response to the powdery mildew fungus (Blumeria graminis f.sp. hordei) in barley leaves [15] and in roots as reaction to Pyrenophora graminea [16]
Summary
Class III plant peroxidases (EC 1.11.1.7; Prxs) are enzymes that catalyze oxidoreduction between H2O2 and various reductants and are involved in a broad range of physiological processes, including plant defense [1] Because they are induced by fungi [2], bacteria [3,4], viruses [5] and viroids [6], they are considered as pathogenesisrelated (PR) proteins, belonging to the PR-protein 9 subfamily [7]. HvPrx was implicated as a susceptibility factor in barley, enhancing successful haustorium formation by the powdery mildew fungus [17]. Another peroxidase of barley, HvPrx is pathogen-induced at the mRNA as well as protein level [15]. There is no evidence that allelic variation of peroxidases directly determines levels of disease resistance
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