Abstract
Spotted leaf mutant belongs to a class of mutants that can produce necrotic lesions spontaneously in plants without any attack by pathogens. These mutants have no beneficial effect on plant productivity but provide a unique opportunity to study programmed cell death in plant defense responses. A novel rice spotted leaf mutant (spl30) was isolated through low-energy heavy ion irradiation. Lesion expression was sensitive to light and humidity. The spl30 mutant caused a decrease in chlorophyll and soluble protein content, with marked accumulation of reactive oxygen species (ROS) around the lesions. In addition, the spl30 mutant significantly enhanced resistance to rice bacterial blight (X. oryzae pv. oryzae) from China (C1-C7). The use of SSR markers showed that the spl30 gene was located between markers XSN2 and XSN4. The genetic distance between the spl30 gene and XSN2 and between spl30 and XSN4 was 1.7 cM and 0.2 cM, respectively. The spl30 gene is a new gene involved in lesion production and may be related to programmed cell death in rice. The ability of this mutant to confer broad resistance to bacterial blight provides a model for studying the interaction between plants and pathogenic bacteria.
Highlights
Plants that develop spontaneous necrotic lesions in the absence of infection by pathogens, environmental stress and mechanical damage are known as lesion mimic mutants (Wang, 2005)
The distribution of spots differed between plants grown in natural field conditions and those grown in a greenhouse (Figure 1)
Scanning electron microscopy (SEM) showed that the surface of wild-type leaves was very clean while that of spl30 mutants containing lesions had many spheres ~1 mm in diameter (Figure 2); these spheres were suspected to be apoptotic bodies formed during apoptosis
Summary
Plants that develop spontaneous necrotic lesions in the absence of infection by pathogens, environmental stress and mechanical damage are known as lesion mimic mutants (Wang, 2005) Such mutants have been reported in many plants, including maize (Hoisington et al, 1982), Arabidopsis (Lorrain et al, 2003), soybean (Badigannavar et al, 2002) and rice (Takahashi et al, 1999). Reactive oxygen species (ROS) such as superoxide (O2-), hydrogen peroxide (H2O2) and hydroxyl radicals (-OH) are produced under environmental stress or as byproducts of normal biochemical processes (Jabs et al., 1996) These ROS usually adversely affect cellular metabolism and membrane structure (Lorrain et al, 2003). Plants have several physiological mechanisms and structural adaptations for detoxifying ROS and for protecting themselves from different types of stress, including pathogens
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