Abstract
Premature leaf senescence affects plant yield and quality, and numerous researches about it have been conducted until now. In this study, we identified an early senescent mutant es4 in rice (Oryza sativa L.); early senescence appeared approximately at 60 dps and became increasingly senescent with the growth of es4 mutant. We detected that content of reactive oxygen species (ROS) and malondialdehyde (MDA), as well as activity of superoxide dismutase (SOD) were elevated, while chlorophyll content, soluble protein content, activity of catalase (CAT), activity of peroxidase (POD) and photosynthetic rate were reduced in the es4 mutant leaves. We mapped es4 in a 33.5 Kb physical distance on chromosome 4 by map-based cloning. Sequencing analysis in target interval indicated there was an eight bases deletion mutation in OsCPK12 which encoded a calcium-dependent protein kinase. Functional complementation of OsCPK12 in es4 completely restored the normal phenotype. We used CRISPR/Cas9 for targeted disruption of OsCPK12 in ZH8015 and all the mutants exhibited the premature senescence. All the results indicated that the phenotype of es4 was caused by the mutation of OsCPK12. Overexpression of OsCPK12 in ZH8015 enhanced the net photosynthetic rate (Pn) and chlorophyll content. OsCPK12 was mainly expressed in green organs. The results of qRT-PCR analysis showed that the expression levels of some key genes involved in senescence, chlorophyll biosynthesis, and photosynthesis were significantly altered in the es4 mutant. Our results demonstrate that the mutant of OsCPK12 triggers the premature leaf senescence; however, the overexpression of OsCPK12 may delay its growth period and provide the potentially positive effect on productivity in rice.
Highlights
Senescence is a series of deteriorative processes including death and decomposition of cell, degradation of organization and organ, and the aging of the life function
The results revealed that ES4 was ubiquitously expressed in many organs, indicated that the mutation of ES4 was responsible for the decline and it was mainly expressed in photosynthetic organs such as of photosynthetic ability and the content of chlorophylls in es4. stems and sheaths, especially in leaves (Figure 7A)
These toxic reactive oxygen species (ROS) can result in lipid peroxidation, cellular damage and cell death, and genetic evidence suggests that ROS as a signaling molecule plays a major role in the senescence process by genetically activating programmed pathways of gene expression (Foyer and Noctor, 2005)
Summary
Senescence is a series of deteriorative processes including death and decomposition of cell, degradation of organization and organ, and the aging of the life function. Leaf senescence as a type of programmed cell death (PCD) is a critical process for the adaptability of plants (Himelblau, 2000). As a complex physiological process, leaf senescence is influenced by external environment such as temperature, light, drought, nutrient deficiency, wounding, pathogen infection, etc. Premature leaf senescence has a direct impact on crop yields by changing the duration of photosynthesis, and modifying the nutrient remobilization efficiency and harvest index (Wu et al, 2012). As one of the major food crops, rice feeds nearly half of the world’s population, but rice leaf premature senescence often results in the reduction in yield and quality. On the contrary, delayed leaf senescence shows potentially positive effects on rice productivity. Understanding the molecular mechanism of leaf senescence is important for breeders in raising rice production and quality
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