Impaired Function of the Calcium-Dependent Protein Kinase, OsCPK12, Leads to Early Senescence in Rice (Oryza sativa L.)
Beifang WangYingxin ZhangZhenzhen BiQunen LiuTingting XuNing YuYongrun CaoAike ZhuWeixun WuXiaodeng ZhanGalal Bakr AnisPing YuDaibo ChenShihua ChengLiyong Cao
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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 malonaldehyde (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 33.5Kb 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.Keywords:
Senescence
Amber mutants of bacteriophage BF23 were classified into two functional groups, types I and II, by the yields of the infecting-mutant genotypes in plate complementation tests. Type I mutants produced their genotypes at levels more than 20% of the total progeny phages, and type II mutants did so at levels of less than 5%. Comparison of the results of plate complementation tests with those of extract complementation tests revealed that all the type I mutants were defective in the tail formation, while most type II mutants were defective in the formation of either mature heads (type IIa) or both mature heads and tails (type IIb). Since in extract complementation tests the activated phages are always of genotypes corresponding to mutations defective in only the tail formation, the plate complementation test is comparable with the extract complementation test when judged on the basis of the yield of the mutant genotypes. Of 29 complementation groups, 8 type I, 14 type IIa, and 5 type IIb mutants were identified. Previously, amber mutations of BF23 were mapped on four genetic segments. These segments were ordered in one linkage map by crosses between deletion and amber mutants.
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Protein-fragment complementation assay
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In order to clarify the important physiological effect of nitrogen on plant exposed to heavy metals,poplar plants were used as experimental material and treated with CdCl2plus NH4HCO3,CdCl2and NH4HCO3,respectively. After 60 days of treatment,plant growth,relative content of precursor of chlorophyll synthesis and chloroplast ultrastructure were detected. Results showed that plant height,dry weight and chlorophyll content of the plants exposed to Cd all significantly decreased when compared to the controls. Cd seriously destroyed chloroplast ultrastructure and inhibited Chl synthesis. The blocking site located on the steps between UrogenIII and Coprogen III; nitrogen addition could promote the growth,increase content of chlorophyll of plants under stress of Cd,and well protect the chloroplast ultrastructure, effectively alleviate the inhibition of Cd to chlorophyll synthesis by unblocking the pathway. The above results demonstrated that nitrogen played an important role in detoxifying heavy metals from plants.
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Hill reaction
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Hydrogen sulfide (H2S), a novel gasotransmitter in both mammals and plants, plays important roles in plant development and stress responses. Leaf senescence represents the final stage of leaf development. The role of H2S-producing enzyme L-cysteine desulfhydrase in regulating tomato leaf senescence is still unknown. In the present study, the effect of an L-cysteine desulfhydrase LCD1 on leaf senescence in tomato was explored by physiological analysis. LCD1 mutation caused earlier leaf senescence, whereas LCD1 overexpression significantly delayed leaf senescence compared with the wild type in 10-week tomato seedlings. Moreover, LCD1 overexpression was found to delay dark-induced senescence in detached tomato leaves, and the lcd1 mutant showed accelerated senescence. An increasing trend of H2S production was observed in leaves during storage in darkness, while LCD1 deletion reduced H2S production and LCD1 overexpression produced more H2S compared with the wild-type control. Further investigations showed that LCD1 overexpression delayed dark-triggered chlorophyll degradation and reactive oxygen species (ROS) accumulation in detached tomato leaves, and the increase in the expression of chlorophyll degradation genes NYC1, PAO, PPH, SGR1, and senescence-associated genes (SAGs) during senescence was attenuated by LCD1 overexpression, whereas lcd1 mutants showed enhanced senescence-related parameters. Moreover, a correlation analysis indicated that chlorophyll content was negatively correlated with H2O2 and malondialdehyde (MDA) content, and also negatively correlated with the expression of chlorophyll degradation-related genes and SAGs. Therefore, these findings increase our understanding of the physiological functions of the H2S-generating enzyme LCD1 in regulating leaf senescence in tomato.
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Malondialdehyde
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Cystathionine gamma-lyase
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Abstract Background Heat stress is a major environmental factor that could induce premature leaf senescence in plants. So far, a few rice premature senescent leaf mutants have been reported to involve in heat tolerance. Findings We identified a premature senescence leaf 50 ( psl50 ) mutant that exhibited a higher heat susceptibility with decreased survival rate, over-accumulated hydrogen peroxide (H 2 O 2 ) content and increased cell death under heat stress compared with the wild-type. The causal gene PREMATURE SENESCENCE LEAF 50 ( PSL50 ) was isolated by using initial map-based resequencing (IMBR) approach, and we found that PSL50 promoted heat tolerance probably by acting as a modulator of H 2 O 2 signaling in response to heat stress in rice ( Oryza sativa L.). Conclusions PSL50 negatively regulates heat-induced premature leaf senescence in rice.
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Rice plant
Oryza
Plant Physiology
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Abstract Yellow mutant is an important material for studying chlorophyll biosynthesis, degradation and the genetics and development of chloroplasts. The chlorophyll biosynthesis and degradation pathways of tomato (Solanum lycopersicum) mutant ym (Yellow mutant) and control zs4 (Zhongshu 4) were studied. Photosynthetic parameters and chlorophyll fluorescence parameters of the variety ym and zs4 were measured. The results showed that ym was more sensitive than the variety ZS4, while the variety ym has more tolerant to low light. The chloroplasts in ym exhibited onset of degradation compared with zs4 under the transmission electron microscopy (TEM). The lack of chlorophyll-protecting material or the chloroplast grana degradation causes the leaf fade.
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Chlorophyll b
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Abstract BackgroundHeat stress is a major environmental factor that could induce premature leaf senescence in plants. So far, few rice premature senescent leaf mutants have been reported to involve in heat tolerance.FindingsWe identified a premature senescence leaf 50 ( psl50 ) mutant that exhibited a higher heat susceptibility with decreased survival rate, over-accumulated hydrogen peroxide (H 2 O 2 ) content and increased cell death under heat stress compared with the wild-type. The causal gene PREMATURE SENESCENCE LEAF 50 ( PSL50 ) was isolated by using initial map-based resequencing (IMBR) approach, and we found that PSL50 promoted heat tolerance probably by acting as a modulator of H 2 O 2 signaling in response to heat stress in rice ( Oryza sativa L.).Conclusions PSL50 negatively regulates heat-induced premature leaf senescence in rice.
Senescence
Rice plant
Oryza
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The chloroplast numbers,morphologies and ultra-structures in the leaves of a xantha wheat mutants etiolating naturally and its parent(Xinong1718) were comparatively examined by transmission electron microscopy.It was shown that the mutant plants with three etiolating degrees did not obviously differ in chloroplast distribution,number,shape and size from the mutant parent;(2) Yellowish-green plants whose chlorophyll content was 58% of the wild type did not obviously differed in chloroplast ultra-structure from the parent,but their stroma-thylakoids and granum-thylakoids were highly differentiated and their granum and grana lamellae were relatively plentiful;(3) The chlorophyll contents of the golden and greenish-yellow plants were separately 17% and 24% of that of the wild type and their chloroplast ultra-structures obviously differed from that of the parent and the chloroplasts of the mutant plants had clear developmental defect,the chloroplasts of golden plants containing no grana,obviously visible stroma lamellae,starch grains and plentiful osmiophilic granules and those of greenish-yellow mutant plants containing grana whose number was obviously lower than that in the chloroplasts of the parent and that had a fewer layers of stroma lamellae,and highly developed granum-thylakoids.The results indicted that the change in the chloroplast ultra-structure of the xantha wheat mutant resulted from lowered chlorophyll content and it was supposed that the etiolating mutation resulted from chlorophyll synthesis blockade.
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A chlorophyll-deficient mutant of pea (Pisum sativum) was found as a spontaneous mutation of the variety Greenfeast. Total chlorophyll of the mutant leaves was about one-half that of normal pea leaves per mg dry weight, and the ratio of chl a:chl b ranged from 10 to 18, compared with 3 for normal pea. In each generation the mutant plants gave rise to normal and mutant plants and lethal plants with yellow leaves. For a normal pea plant, CO2 uptake was saturated at about 60,000 lux, whereas with mutant leaves, the rate of CO2 uptake was still increasing at 113,000 lux. At 113,000 lux the mutant and normal leaves showed similar rates of CO2 fixation per unit area of leaf surface, but on a chlorophyll basis the mutant leaves were twice as active. Hill reaction measurements on isolated chloroplasts also showed that the mutant chloroplasts were saturated at higher intensities than the normal, and that the activity of the mutant was at least double that of the normal on a chlorophyll basis. It is suggested that the photosynthetic units of the mutant chloroplasts contain about half the number of chlorophyll molecules as compared to the normal photosynthetic units. Electron microscopy of leaf sections of normal and mutant leaves showed that the mutant chloroplasts contain fewer lamellae per chloroplast and fewer lamellae per granum. The lethal chloroplasts, which were virtually devoid of chlorophyll, were characterized by an absence of grana.
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Abstract Chlorophyll contents of leaves of sugar beets undergoing Fe stress have been shown to be correlated positively with leaf Fe concentration (Plant Physiol. 1980 65:114–120). In the present work, the nature of this quantitative relationship was explored by determining the amounts of leaf Fe associated with whole chloroplasts (isolated nonaqueously) and with EDTA‐washed chloroplast lamellae. The results show that leaf chlorophyll content was quantitatively related to the leaf content of chloroplast Fe and to the leaf content of chloroplast lamellar Fe. Nonaqueously isolated chloroplasts accounted for 79 and 73 percent of the Fe of leaves of Fe sufficient and Fe deficient plants, respectively. The Fe content of EDTA‐washed chloroplast lamellae constituted 58 percent of leaf Fe in control plants; this increased to 75 percent in Fe deficient plants. In contrast with the view that chlorophyll contents may be correlated with a "biochemically active fraction" of leaf Fe (e.g. water or acid soluble fractions), these results imply that chlorophyll content is quantitatively related to the bound Fe content of the chloroplast lamellae. In addition, we postulate that Fe deficiency may reduce chlorophyll and lamellar Fe contents concomitantly by retarding the formation of new thylakoids, of which chlorophyll and Fe are integral constituents, rather than by diminishing chlorophyll synthesis per se.
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