Abstract
BackgroundSpotted leaf mutants show typical necrotic lesions that appear spontaneously in the absence of any pathogen attack. These mutants are often characterized to exhibit programmed cell death (PCD) and activation of plant defense responses resulting in enhanced disease resistance to multiple pathogens. Here, we reported a novel spotted-leaf mutant, spl40 that showed enhanced disease resistance response.ResultsInitially lesions appeared at leaf tips during seedling stage and gradually covered the whole leaf at the tillering stage. The lesion development was light-dependent. spl40 showed obvious cell death at and around the lesion, and burst of reactive oxygen species (ROS) was accompanied by disturbed ROS scavenging system. Photosynthetic capacity was compromised as evidenced by significant reductions in chlorophyll content, important photosynthesis parameters and downregulated expression of photosynthesis-related genes which ultimately led to poor performance of major agronomic traits. spl40 exhibited enhanced resistance to 14 out of 16 races of bacterial blight pathogen of rice, caused by Xanthomonas oryzae pv. oryzae, most probably though activation of SA and JA signaling pathways, owing to upregulated expression of SA and JA signaling genes, though the exact mechanism remain to be elucidated. The spotted-leaf phenotype was controlled by a novel single recessive nuclear gene. Genetic mapping combined with high throughput sequencing analysis identified Os05G0312000 as the most probable candidate gene. Sequencing of ORF revealed a single SNP change from C to T that resulted in non-synonymous change in amino acid residue from leucine to phenylalanine. Interestingly, the complementation plants did not display lesions before heading but showed lesions at the heading stage and the transgenic T1 progenies could be classified into 3 categories based on their lesion intensity, indicating the complex genetic nature of the spl40 mutation.ConclusionThe results obtained here clearly show that genes related to defense and PCD were upregulated in accordance with enhanced disease resistance and occurrence of PCD, whereas the photosynthetic capacity and overall ROS homeostasis was compromised in spl40. Our data suggest that a novel spotted-leaf mutant, spl40, would help to elucidate the mechanism behind lesion development involving programmed cell death and associated defense responses.
Highlights
Spotted leaf mutants show typical necrotic lesions that appear spontaneously in the absence of any pathogen attack
Genetic and molecular data accumulated till date have suggested that cell death in plants associated with hypersensitive response (HR) or developmental processes is genetically programmed (Lorrain et al 2003), and this cell death is believed to be programmed cell death that plays an important role in plant growth and development (Huang et al 2010)
There was a significant decrease in the soluble protein content in spl40 at the seedling and tillering stages compared to wild type (WT) (Fig. 1f)
Summary
Spotted leaf mutants show typical necrotic lesions that appear spontaneously in the absence of any pathogen attack These mutants are often characterized to exhibit programmed cell death (PCD) and activation of plant defense responses resulting in enhanced disease resistance to multiple pathogens. We reported a novel spotted-leaf mutant, spl that showed enhanced disease resistance response Plants, during their lifecycle, are exposed to adverse environmental conditions imposed by different biotic and abiotic stresses. Many LMM with disease resistance phenotype showed the elevated expression of pathogenesis-related proteins like PR1, PR2, PR5, PR10, PBZ1 and PAL, which are the important components of plant defense against pathogens (Wang et al 2005; Mori et al 2007; Takahashi et al 2007; Qiao et al 2010; Chen et al 2012)
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