Abstract
Premature leaf senescence negatively impacts the grain yield in the important monocot rice (Oryza sativa L.); to understand the molecular mechanism we carried out a screen for mutants with premature senescence leaves in a mutant bank generated by ethyl methane sulfonate (EMS) mutagenesis of elite indica rice ZhongJian100. Five premature senescence leaf (psl15, psl50, psl89, psl117 and psl270) mutants were identified with distinct yellowish phenotypes on leaves starting from the tillering stage to final maturation. Moreover, these mutants exhibited significantly increased malonaldehyde content, decreased chlorophyll content, reduced numbers of chloroplast and grana thylakoid, altered photosynthetic ability and expression of photosynthesis-related genes. Furthermore, the expression of senescence-related indicator OsI57 was significantly up-regulated in four mutants. Histochemical analysis indicated that cell death and reactive oxygen species (ROS) accumulation occurred in the mutants with altered activities of ROS scavenging enzymes. Both darkness and abscisic acid (ABA) treatments could induce leaf senescence and resulted in up- or down-regulation of ABA metabolism-related genes in the mutants. Genetic analysis indicated that all the premature senescence leaf mutants were controlled by single non-allelic recessive genes. The data suggested that mechanisms underlying premature leaf senescence are likely different among the mutants. The present study would facilitate us to further fine mapping, cloning and functional characterization of the corresponding genes mediating the premature leaf senescence in rice.
Highlights
Leaf senescence is the final stage of leaf development, in which intracellular organelles and macromolecules are actively destabilized to relocate nutrients into developing tissues or storage organs [1]
Obvious retarded growth occurred both in psl89 and psl117 mutants compared with wild type (WT) (Figure 1D,E)
With the development of the plants, the mutants displayed a very significant premature senescence phenotype with deep-yellowing and wilted leaves at the heading and grain-filling stage compared with WT (Figure 1G–L)
Summary
Leaf senescence is the final stage of leaf development, in which intracellular organelles and macromolecules are actively destabilized to relocate nutrients into developing tissues or storage organs [1]. The most striking feature of premature senescence leaf mutants is the leaf yellowish phenotype due to the breakdown of chlorophyll during chloroplast degeneration and hydrolysis of macromolecules such as proteins and nucleic acids, which results in mitochondria and nuclei dissociation and cell death [4,5]. We identified five premature leaf senescence mutants (psl, psl, psl, psl117 and psl270) from an ethyl methane sulfonate (EMS) mutant bank of rice cultivar ZhongJian100 We further characterized their performance on agronomic traits, their physio-biochemical properties including chlorophyll contents, chloroplast structure, photosynthetic ability, response to darkness and ABA, expression profile of ABA and senescence-related genes and the genetic controls of their premature senescence phenotypes. Our results would provide the basis for the isolation of these premature senescence genes and the elucidation of the senescence mechanism in rice
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