Leaf Senescence Mutant Research Articles

Mapping the gene of a maize leaf senescence mutant and understanding the senescence pathways by expression analysis.

Narrowing down to a single putative target gene behind a leaf senescence mutant and constructing the regulation network by proteomic method. Leaf senescence mutant is an important resource for exploring molecular mechanism of aging. To dig for potential modulation networks during maize leaf aging process, we delimited the gene responsible for a premature leaf senescence mutant els5 to a 1.1Mb interval in the B73 reference genome using a BC1F1 population with 40,000 plants, and analyzed the leaf proteomics of the mutant and its near-isogenic wild type line. A total of 1355 differentially accumulated proteins (DAP) were mainly enriched in regulation pathways such as "photosynthesis", "ribosome", and "porphyrin and chlorophyll metabolism" by the KEGG pathway analysis. The interaction networks constructed by incorporation of transcriptome data showed that ZmELS5 likely repaired several key factors in the photosynthesis system. The putative candidate proteins for els5 were proposed based on DAPs in the fined QTL mapping interval. These results provide fundamental basis for cloning and functional research of the els5 gene, and new insights into the molecular mechanism of leaf senescence in maize.

Analysis of physiological characteristics of early leaf senescence mutant <italic>w14</italic> and its gene mapping for rice

<p indent=0mm>Leaf senescence has important effects on yield and quality of rice. In this study, a mutant <italic>w14</italic> of early leaf senescence was derived from <italic>japonica</italic> variety, Yunyin (YY) by ethylmethylsulfone (EMS) mutagenesis. The physiological and histological changes of the mutant <italic>w14</italic> were studied during the whole growth and development period. The results indicated that the growing vigor of the mutant <italic>w14</italic> was not only weak and slow from the full tillering stage, but also the early leaf senescence appeared obviously at the heading stage. At last the whole plant for the mutant <italic>w14</italic> appeared senescence and wilt. The submicroscopic structure observation indicated that the vesicular cells of leaves surface were not only damaged, but the cell structure was loose and their integrity decreased. The number of nuclei from the mutant cells was decreased significantly and intracellular nuclear degraded. The contents of leaves chlorophyll between WT and the mutant <italic>w14</italic> were analyzed at the seedling stage and adult stage respectively, indicating that the difference was not significant among chlorophyll <italic>a</italic>, chlorophyll <italic>b</italic> and carotenoid between WT and the mutant <italic>w14</italic> at the seedling stage. But the contents for chlorophyll <italic>a</italic>, chlorophyll <italic>b</italic> and carotenoid of the mutant <italic>w14</italic> were significantly less than those of wild type (WT) at the adult stage, decreased by 15.5%, 37.6%, and 10.3%, respectively, and total chlorophyll content decreased by 20.6%. Moreover, the characteristics for antioxidant were analyzed for wild type and the mutant <italic>w14</italic>, including the activity of POD, SOD, CAT, MDA, LPO and so on, indicating that the POD activity of the mutant <italic>w14</italic> was much less than that of WT, decreased by 7.42% at the seedling stage, but decreased 9.52% compared with WT at the adult stage. Data of SOD activity indicated that the SOD activity of the mutant <italic>w14</italic> was much more than that of WT, increased by 15.5% at the seedling stage. But the difference was not significant for SOD activity between WT and the mutant <italic>w14</italic> at the adult stage. The catalase activity showed that the CAT activity of the mutant <italic>w14</italic> was not significantly different from WT at the seedling stage. The CAT activity of <italic>w14</italic> was much less than WT at the adult stage. The MDA content showed that the MDA content in the leaves of <italic>w14</italic> was not much different from WT, while the MDA content of <italic>w14</italic> increased 37.4% at the adult stage. The LPO content of <italic>w14</italic> was much more than that of WT at seedling stage and adult stage, increased by 19.2% and 20.6%, respectively. At last, the target gene <italic>w14</italic> was fine mapped in a physical interval of about 76 kb between InDel markers 3-7 and 3-9 on chromosome 3 in rice. There were 8 candidate genes in this interval region, laid a basis for cloning and functional analysis of the gene <italic>w14</italic> in the future.

Fine mapping and candidate gene analysis of leaf tip premature senescence and Dwarf Mutant dls-1 in Rice

Premature leaf senescence negatively affects rice yield and quality. Identifying premature senescence mutants and examining their gene functions are important for the genetic improvement of crops. In this study, a leaf senescence mutant dls-1 was obtained from japonica Yundao by ethyl methane sulfonate mutagenesis, which showed the phenotypes of premature leaf senescence, reduced plant height and decreased yield-associated traits including panicle length, seed setting rate, and 1000-grain weight. Biochemical analysis revealed the accumulation of reactive oxygen species in dls-1 leading to increased apoptosis rates, stomata length extension, higher water loss, and a decline in leaf silicification. Transcriptomic data showed that pathogen resistance-related genes were down-regulated in dls-1, causing increased sensitivity to bacterial-induced blight. Genetic analysis indicated that the mutant trait of dls-1 was controlled by a single recessive nuclear gene, and the gene was fine-mapped to a 159 kb region on rice chromosome 1 using map-based cloning strategy. A total of 23 open reading frames were found in the interval, and no similar phenotypic genes have been reported. However, all candidate coding genes and promoter regions were sequenced, and no mutation sites were found. RNA-seq analysis and qRT-PCR showed that the candidate gene LOC_Os01g71670, encodes a rice endo-1,3-β-glucanase, showed significantly different expression levels in dls-1 compared to the wild-type. LOC_Os01g71670 is highly homologous with GII in barley, and Gns4 and glu1 in rice, which participates in the hormone response pathway affecting plant growth and development, and also involve in the regulation of PR2 expression. Taken together with the phenotypes of dls-1, we conclude that LOC_Os01g71670 may be the candidate gene, causing the premature senescence of the leaf tip and loss of pathogen resistance.

OsNBL1, a Multi-Organelle Localized Protein, Plays Essential Roles in Rice Senescence, Disease Resistance, and Salt Tolerance

BackgroundPlant senescence is a complicated process involving multiple regulations, such as temperature, light, reactive oxygen species (ROS), endogenous hormone levels, and diseases. Although many such genes have been characterized to understand the process of leaf senescence, there still remain many unknowns, and many more genes need to be characterized.ResultsWe identified a rice mutant nbl1 with a premature leaf senescence phenotype. The causative gene, OsNBL1, encodes a small protein with 94 amino acids, which is conserved in monocot, as well as dicot plants. Disruption of OsNBL1 resulted in accelerated dark-induced leaf senescence, accompanied by a reduction in chlorophyll content and up-regulation of several senescence-associated genes. Notably, the nbl1 mutant was more susceptible to rice blast and bacterial blight but more tolerant to sodium chloride. Several salt-induced genes, including HAK1, HAK5, and three SNAC genes, were also up-regulated in the nbl1 mutant. Additionally, the nbl1 mutant was more sensitive to salicylic acid. Plants overexpressing OsNBL1 showed delayed dark-induced senescence, consistent with a higher chlorophyll content compared to wild-type plants. However, the overexpression plants were indistinguishable from the wild-types for resistance to the rice blast disease. OsNBL1 is a multi-organelle localized protein and interacts with OsClpP6, which is associated with senescence.ConclusionsWe described a novel leaf senescence mutant nbl1 in rice. It is showed that OsNBL1, a multi-organelle localized protein which interacts with a plastidic caseinolytic protease OsClpP6, is essential for controlling leaf senescence, disease resistance, and salt tolerance.

Identification and gene mapping of the starch accumulation and premature leaf senescence mutant ossac4 in rice

The rice mutant ossac4 (starch accumulating 4) was raised from seeds of the rice (Oryza sativa L.) indica maintainer line Xinong 1B treated with ethyl methanesulfonate. The distal and medial portions of the second leaf displayed premature senescence in the ossac4 mutant at the four-leaf stage. Physiological and biochemical analysis, and cytological examination revealed that the ossac4 mutant exhibited the premature leaf senescence phenotype. At the four-leaf stage, the leaves of the ossac4 mutant exhibited significantly increased contents of starch compared with those of the wild type (WT). Quantitative real-time PCR analysis showed that the expression levels of photosynthesis-associated genes were down-regulated and the expression levels of glucose metabolism-associated genes were abnormal. Genetic analysis indicated that the ossac4 mutation was controlled by a single recessive nuclear gene. The OsSAC4 gene was localized to a 322.7-kb interval between the simple-sequence repeat marker XYH11-90 and the single-nucleotide polymorphism marker SNP5300 on chromosome 11. The target interval contained 20 annotated genes. The present results demonstrated that ossac4 represents a novel starch accumulation and premature leaf senescence mutant, and lays the foundation for cloning and functional analysis of OsSAC4.

Glycosyltransferase-Like RSE1 Negatively Regulates Leaf Senescence Through Salicylic Acid Signaling in Arabidopsis.

Leaf senescence is a developmental process designed for nutrient recycling and relocation to maximize growth competence and reproductive capacity of plants. Thus, plants integrate developmental and environmental signals to precisely control senescence. To genetically dissect the complex regulatory mechanism underlying leaf senescence, we identified an early leaf senescence mutant, rse1. RSE1 encodes a putative glycosyltransferase. Loss-of-function mutations in RSE1 resulted in precocious leaf yellowing and up-regulation of senescence marker genes, indicating enhanced leaf senescence. Transcriptome analysis revealed that salicylic acid (SA) and defense signaling cascades were up-regulated in rse1 prior to the onset of leaf senescence. We found that SA accumulation was significantly increased in rse1. The rse1 phenotypes are dependent on SA-INDUCTION DEFICIENT 2 (SID2), supporting a role of SA in accelerated leaf senescence in rse1. Furthermore, RSE1 protein was localized to the cell wall, implying a possible link between the cell wall and RSE1 function. Together, we show that RSE1 negatively modulates leaf senescence through an SID2-dependent SA signaling pathway.

Senescence‐related translocation of nonstructural carbohydrate in rice leaf sheaths under different nitrogen supply

AbstractThe translocation of nonstructural carbohydrates (NSC) from leaf sheaths to filling grains after anthesis contributed greatly to the grain yield of cereal crops. In this study, the effect of nitrogen (N) supply levels on the accumulation and translocation of NSC in leaf sheath tissues and its relationship with the initiation and progression of leaf senescence during grain filling was investigated using two rice (Oryza sativa L.) genotypes, namely, premature flag leaf senescence mutant (psf) and its wild‐type. Three N treatment levels were used to examine N‐supply induced alteration in the activities of several key enzymes involved in NSC translocation and N assimilation in different leaf sheaths. The results show that the NSC translocation rate in leaf sheaths under low nitrogen (LN) treatment was significantly higher than those under normal nitrogen (NN) and high nitrogen (HN) treatments. However, the positive effect of LN on the NSC translocation in leaf sheath was closely associated with its negative effect on grain yield, due to accelerated leaf senescence and shortened leaf longevity. Comparatively, the upper‐positional sheath had a lower NSC amount and higher NSC translocation rate than the lower‐leaf sheaths after heading. High N suppressed sucrose‐phosphate synthase (SPS) activity in leaf sheaths, but enhanced the activity of key enzymes involving in N assimilation in leaf sheaths. The upper sheath had higher activity of sucrose‐metabolizing enzymes and lower activity of N‐assimilating enzymes. Hence, the upper‐leaf sheath had a relatively weak N assimilation and stronger NSC translocation than the lower‐leaf sheaths.

Molecular mapping of a novel early leaf-senescence gene Els2 in common wheat by SNP genotyping arrays

Early leaf senescence in wheat (Triticum aestivum L.) is one of the limiting factors for developing high yield potential. In this study, a stably inherited, early leaf-senescence mutant LF2099 was initially identified in an M2 population of the common wheat accession H261 after ethyl methanesulfonate (EMS) mutagenesis. Early leaf senescence was observed in the LF2099 mutant during the three-leaf-stage, and then the etiolated area of the wheat leaf increased gradually from the bottom to the top throughout development. Compared with H261, the chlorophyll (Chl a, Chl b) and carotenoid contents and photosynthetic capacity of the mutant were significantly decreased. All of its yield-related traits except for spike length were also significantly reduced. Dissolved cytoplasm, abnormal chloroplast structure, dissolved chloroplast membrane, abnormal thylakoid development, and more plastoglobules were observed in the senescent leaf region of the mutant by transmission electronic microscope. Genetic analysis indicated that the early leaf-senescence phenotype is controlled by an incomplete-dominance nuclear gene, here designated Els2. Using single nucleotide polymorphisms and bulked segregant analysis, the els2 gene was anchored in a region on chromosome 2BL between simple sequence repeat (SSR) markers gpw4043 and wmc149. Six new polymorphic SSR markers were developed from the Chinese Spring 2BL shotgun survey sequence contigs. By means of comparative genomics analyses, the collinearity genomic regions of the els2 locus on wheat 2BL were identified in Brachypodium distachyon chromosome 5, rice (Oryza sativa) chromosome 4 and sorghum (Sorghum bicolor) chromosome 6. Five intron polymorphism (IP) markers were further developed from this collinearity genomic region. Ultimately, Els2 was mapped in a genetic interval of 0.95 cM flanked by IP markers 2BIP09 and 2BIP14. The co-segregating IP markers 2BIP12 and 2BIP17 provide a starting point for the fine mapping and map-based cloning of Els2.

Characterization and Mapping of a Novel Premature Leaf Senescence Mutant in Common Tobacco (Nicotiana tabacum L.).

As the last stage of plant development, leaf senescence has a great impact on plant’s life cycle. Genetic manipulation of leaf senescence has been used as an efficient approach in improving the yield and quality of crop plants. Here we describe an ethyl methane sulfonate (EMS) mutagenesis induced premature leaf senescence mutant yellow leaf 1 (yl1) in common tobacco (Nicotiana tabacum L.). The yl1 plants displayed early leaf yellowing. Physiological parameters and marker genes expression indicated that the yl1 phenotype was caused by premature leaf senescence. Genetic analyses indicated that the yl1 phenotype was controlled by a single recessive gene that was subsequently mapped to a specific interval of tobacco linkage group 11 using simple sequence repeat (SSR) markers. Exogenous plant hormone treatments of leaves showed that the yl1 mutant was more sensitive to ethylene and jasmonic acid than the wild type. No similar tobacco premature leaf senescence mutants have been reported. This study laid a foundation for finding the gene controlling the mutation phenotype and revealing the molecular regulation mechanism of tobacco leaf senescence in the next stage.

Disruption of a Upf1-like helicase-encoding gene OsPLS2 triggers light-dependent premature leaf senescence in rice.

The OsPLS2 locus was isolated and cloned by map-based cloning that encodes a Upf1-like helicase. Disruption of OsPLS2 accelerated light-dependent leaf senescence in the rice mutant of ospls2. Leaf senescence is a very complex physiological process controlled by both genetic and environmental factors, however its underlying molecular mechanisms remain elusive. In this study, we report a novel Oryza sativa premature leaf senescence mutant (ospls2). Through map-based cloning, a G-to-A substitution was determined at the 1st nucleotide of the 13th intron in the OsPLS2 gene that encodes a Upf1-like helicase. This mutation prompts aberrant splicing of OsPLS2 messenger and consequent disruption of its full-length protein translation, suggesting a negative role of OsPLS2 in regulating leaf senescence. Wild-type rice accordingly displayed a progressive drop of OsPSL2 protein levels with age-dependent leaf senescence. Shading and light filtration studies showed that the ospls2 phenotype, which was characteristic of photo-oxidative stress and reactive oxygen species (ROS) accumulation, was an effect of irritation by light. When continuously exposed to far-red light, exogenous H2O2 and/or abscisic acid (ABA), the ospls2 mutant sustained hypersensitive leaf senescence. In consistence, light and ROS signal pathways in ospls2 were activated by down-regulation of phytochrome genes, and up-regulation of PHYTOCHROME-INTERACTING FACTORS (PIFs) and WRKY genes, all promoting leaf senescence. Together, these data indicated that OsPLS2 played an essential role in leaf senescence and its disruption triggered light-dependent leaf senescence in rice.

A 22-bp deletion in OsPLS3 gene encoding a DUF266-containing protein is implicated in rice leaf senescence.

Key message The OsPLS3 locus was isolated by map-based cloning that encodes a DUF266-containing protein. OsPLS3 regulates the onset of leaf senescence in rice. Glycosyltransferases (GTs) are one of the most important enzyme groups required for the modification of plant secondary metabolites and play a crucial role in plant growth and development, however the biological functions of most GTs remain elusive. We reported here the identification and characterization of a novel Oryza sativa premature leaf senescence mutant (ospls3). Through map-based cloning strategy, we determined that 22-bp deletion in the OsPLS3 gene encoding a domain of unknown function 266 (DUF266)-containing protein, a member of GT14-like, underlies the premature leaf senescence phenotype in the ospls3 mutant. The OsPLS3 mRNA levels progressively declined with the age-dependent leaf senescence in wild-type rice, implying a negative role of OsPLS3 in regulating leaf senescence. Physiological analysis, and histochemical staining and transmission electron microscopy assays indicated that the ospls3 mutant accumulated higher levels of ethylene and reactive oxygen species than its wild type. Furthermore, the ospls3 mutant showed hypersensitivity to exogenous 1-aminocyclopropane-1-carboxylic acid, H2O2 and high level of cytokinins. Our results indicated that the DUF266-containing gene OsPLS3 plays an important role in the onset of leaf senescence, in part through cytokinin and ethylene signaling in rice.

A guanine insert in OsBBS1 leads to early leaf senescence and salt stress sensitivity in rice (Oryza sativa L.).

A rice receptor-like kinase gene OSBBS1/OsRLCK109 was identified; this gene played vital roles in leaf senescence and the salt stress response. Early leaf senescence can cause negative effects on rice yield, but the underlying molecular regulation is not fully understood. bilateral blade senescence 1 (bbs1), an early leaf senescence mutant with a premature senescence phenotype that occurs mainly performing at the leaf margins, was isolated from a rice mutant population generated by ethylmethane sulfonate (EMS) treatment. The mutant showed premature leaf senescence beginning at the tillering stage and exhibited severe symptoms at the late grain-filling stage. bbs1 showed accelerated dark-induced leaf senescence. The OsBBS1 gene was cloned by a map-based cloning strategy, and a guanine (G) insertion was found in the first exon of LOC_Os03g24930. This gene encodes a receptor-like cytoplasmic kinase and was named OsRLCK109 in a previous study. Transgenic LOC_Os03g24930 knockout plants generated by a CRISPR/Cas9 strategy exhibited similar early leaf senescence phenotypes as did the bbs1 mutant, which confirmed that LOC_Os03g24930 was the OsBBS1 gene. OsBBS1/OsRLCK109 was expressed in all detected tissues and was predominantly expressed in the main vein region of mature leaves. The expression of OsBBS1 could be greatly induced by salt stress, and the bbs1 mutant exhibited hypersensitivity to salt stress. In conclusion, this is the first identification of OsRLCKs participating in leaf senescence and playing critical roles in the salt stress response in rice (Oryza sativa L.).

Transcriptome Analysis of a Premature Leaf Senescence Mutant of Common Wheat (Triticum aestivum L.).

Leaf senescence is an important agronomic trait that affects both crop yield and quality. In this study, we characterized a premature leaf senescence mutant of wheat (Triticum aestivum L.) obtained by ethylmethane sulfonate (EMS) mutagenesis, named m68. Genetic analysis showed that the leaf senescence phenotype of m68 is controlled by a single recessive nuclear gene. We compared the transcriptome of wheat leaves between the wild type (WT) and the m68 mutant at four time points. Differentially expressed gene (DEG) analysis revealed many genes that were closely related to senescence genes. Gene Ontology (GO) enrichment analysis suggested that transcription factors and protein transport genes might function in the beginning of leaf senescence, while genes that were associated with chlorophyll and carbon metabolism might function in the later stage. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed that the genes that are involved in plant hormone signal transduction were significantly enriched. Through expression pattern clustering of DEGs, we identified 1012 genes that were induced during senescence, and we found that the WRKY family and zinc finger transcription factors might be more important than other transcription factors in the early stage of leaf senescence. These results will not only support further gene cloning and functional analysis of m68, but also facilitate the study of leaf senescence in wheat.

Gene Mapping and Cloning of a Premature Leaf Senescence Mutant psls1 in Rice

Gene Mapping and Cloning of a Premature Leaf Senescence Mutant <i>psls1</i> in Rice

The ferredoxin-dependent glutamate synthase (OsFd-GOGAT) participates in leaf senescence and the nitrogen remobilization in rice.

Ferredoxin-dependent glutamate synthase (Fd-GOGAT, EC 1.4.7.1) plays major roles in photorespiration and primary nitrogen assimilation. However, due to no mutant or knockdown lines of OsFd-GOGAT have been reported in rice (Oryza sativa L.), the contribution of OsFd-GOGAT to rice foliar nitrogen metabolism remains little up-to-date. Here, we isolated a rice premature leaf senescence mutant named gogat1, which was reduced in 67% of the total GOGAT enzyme activity in leaves. The gogat1 mutant exhibited chlorosis under natural condition, while showed less extent premature leaf senescence under low light treatment. The gogat1 locus was mapped to a 54.1kb region on chromosome 7, and the sequencing of OsFd-GOGAT showed one substitution (A to T) at the 3017th nucleotide of the open reading frame, leading to the amino-acid substitution of leucine changed to histidine. The gogat1 mutant showed reduced seed setting rate, while the grain protein content in gogat1 mutant was significantly higher than that in wild type. Meanwhile, during the grain-filling stage, total amino acids in the up three leaves and the upmost internode were increased dramatically. The results in this study suggested that OsFd-GOGAT might participate in nitrogen remobilization during leaf senescence, which provides a potential way to improve nitrogen use efficiency in rice.

Characterization and fine-mapping of a novel premature leaf senescence mutant yellow leaf and dwarf 1 in rice

Leaves are the main organs in which photosynthates are produced. Leaf senescence facilitates the translocation of photosynthates and nutrients from source to sink, which is important for plant development and especially for crop yield. However, the molecular mechanism of leaf senescence is unknown. Here, we identified a mutant, yellow leaf and dwarf 1 (yld1), which exhibited decreased plant height and premature leaf senescence. Nitroblue tetrazolium and diamiobenzidine staining analyses revealed that the concentrations of reactive oxygen species were higher in yld1 leaves than in wild type leaves. The photosynthetic pigment contents were significantly decreased in yld1. The yld1 chloroplasts had collapsed and were filled with abnormal starch granules. Combining bulk segregant and MutMap gene mapping approaches, the mutation responsible for the yld1 phenotype was mapped to a 7.3 Mb centromeric region, and three non-synonymous single nucleotide polymorphisms located in three novel genes were identified in this region. The expression patterns of the three candidate genes indicated that LOC_Os06g29380 had the most potential for functional verification. Plant hormone measurements showed that salicylic acid was highly accumulated in yld1 leaves when compared with wild type leaves, and yld1 was more sensitive to salicylic acid than wild type. This work lays the foundation for understanding the molecular regulatory mechanism of leaf senescence, and may reveal new connections among the molecular pathways related to leaf senescence, starch metabolism and salicylic acid signaling.

Characterization and fine mapping of a new early leaf senescence mutant es3(t) in rice

Leaf senescence is an important biological process during leaf growth and development. In this study, we isolated a novel rice mutant, early senescence 3 (es3(t)), from the offspring of the wild-type rice cultivar Wuyunjing 7 after ethyl methanesulfonate mutagenesis. The es3(t) exhibited yellowing leaves, decreased chlorophyll (a and b) and carotenoid contents during the growth period, and abnormal chloroplast structure. Early leaf senescence was accompanied with decreased photosynthesis. The content of abscisic acid was increased in es3(t) mutant, which indicates that abscisic acid probably plays an important role in leaf senescence. The expression levels of senescence-associated transcription factors and senescence-associated genes were increased in the es3(t) plant, and the reactive oxygen species were accumulated in the senescence leaves of es3(t) plants. Genetic analysis demonstrated that early leaf senescence phenotype was controlled by a single recessive nuclear gene. Map-based cloning showed that ES3(t) was located on chromosome 3 with a 35-kb physical interval in the BAC AC097624 which included eight putative open reading frames. Based on these findings, we have identified a novel leaf senescence mutant which is a useful resource for revealing the molecular mechanism of early leaf senescence in rice.

Phenotypic characterization and fine mapping of mps1, a premature leaf senescence mutant in rice (Oryza sativa L.)

Leaves play a key role in photosynthesis in rice plants. The premature senescence of such plants directly reduces the accumulation of photosynthetic products and also affects yield and grain quality significantly and negatively. A novel premature senescence mutant, mps1 (mid-late stage premature senescence 1), was identified from a mutant library consisting of ethyl methane sulfonate (EMS) induced descendants of Jinhui 10, an elite indica restorer line of rice. The mutant allele, mps1, caused no phenotypic differences from the wild type (WT), Jinhui 10, but drove the leaves to turn yellow when mutant plants grew to the tillering stage, and accelerated leaf senescence from the filling stage to final maturation. We characterized the agronomic traits, content of photosynthetic pigments and photosynthetic efficiency of mps1 and WT, and fine-mapped MPS1. The results showed that the MPS1-drove premature phenotype appeared initially on the leaf tips at the late tillering stage and extended to the middle of leaves during the maturing stage. Compared to the WT, significant differences were observed among traits of the number of grains per panicle (–31.7%) and effective number of grains per panicle (–38.5%) of mps1 individuals. Chlorophyll contents among the first leaf from the top (Top 1st), the second leaf from the top (Top 2nd) and the third leaf from the top (Top 3rd) of mps1 were significantly lower than those of WT (P<0.05), and the levels of photosynthetic efficiency from Top 1st to the forth leaf from the top (Top 4th) of mps1 were significantly lower than those of WT (P<0.01). Results from the genetic analysis indicated that the premature senescence of mps1 is controlled by a recessive nuclear gene, and this locus, MPS1 is located in a 37.4-kb physical interval between the markers Indel145 and Indel149 on chromosome 6. Genomic annotation suggested eight open reading frames (ORFs) within this physical region. All of these results will provide informative references for the further researches involving functional analyses and molecular mechanism exploring of MPS1 in rice.

A single cytosine deletion in the OsPLS1 gene encoding vacuolar-type H+-ATPase subunit A1 leads to premature leaf senescence and seed dormancy in rice.

Leaf senescence is a programmed developmental process orchestrated by many factors, but its molecular regulation is not yet fully understood. In this study, a novel Oryza sativa premature leaf senescence mutant (ospls1) was examined. Despite normal development in early seedlings, the ospls1 mutant leaves displayed lesion-mimics and early senescence, and a high transpiration rate after tillering. The mutant also showed seed dormancy attributable to physical (defect of micropyle structure) and physiological (abscisic acid sensitivity) factors. Using a map-based cloning approach, we determined that a cytosine deletion in the OsPLS1 gene encoding vacuolar H(+)-ATPase subunit A1 (VHA-A1) underlies the phenotypic abnormalities in the ospls1 mutant. The OsPSL1/VHA-A1 transcript levels progressively declined with the age-dependent leaf senescence in both the ospls1 mutant and its wild type. The significant decrease in both OsPSL1/VHA-A1 gene expression and VHA enzyme activity in the ospls1 mutant strongly suggests a negative regulatory role for the normal OsPLS1/VHA-A1 gene in the onset of rice leaf senescence. The ospls1 mutant featured higher salicylic acid (SA) levels and reactive oxygen species (ROS) accumulation, and activation of signal transduction by up-regulation of WRKY genes in leaves. Consistent with this, the ospls1 mutant exhibited hypersensitivity to exogenous SA and/or H2O2 Collectively, these results indicated that the OsPSL1/VAH-A1 mutation played a causal role in premature leaf senescence through a combination of ROS and SA signals. To conclude, OsPLS1 is implicated in leaf senescence and seed dormancy in rice.

Physiological Characteristics and Gene Mapping of a Precocious Leaf Senes-cence Mutant ospls3 in Rice

Leaf senescence is the final stage of leaf development. However, premature aging of functional leaves leads to yield reduction and quality decline. Thus, it is very important for developing novel crop germplasms with delayed leaf-senescence characteristics through investigating the molecular mechanism of leaf senescence. In this study, an ospls3 (Oryza sativa preco- cious leaf senescence 3) mutant, produced by 60 Co γ-radiation treatment of indica cultivar N142, was identified. The symptoms of the premature senescence mutant presented firstly at tillering stage showing brown leaf tip and brown spots in top part of leaf blade, then spread rapidly to basal part of leaf blade and led leaf to die. The physiological analysis indicated that, in the ospls3 mutant, the content of chlorophyll was the highest in the flag leaf, the following was in second-top and third-top leaves, but all of them were significantly lower than those in the wild type. The contents of MDA, O2܋ , and H2O2 and the activities of SOD and POD among the top three leaves in the wild type maintained similar levels, which were significantly lower than those in the mu- tant. The soluble protein contents and the activity of CAT had no significant difference among top three leaves in the wild type while significantly decreased in the mutant. Genetic analysis verified that the ospls3 is a recessive mutant and was mapped in a 294 kb interval between RM6953 and RM28753 on the long arm of chromosome 12, which establishes a solid foundation for further cloning and functional studies of this gene.