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.

Rice molecular markers and genetic mapping:Current status and prospects

Dramatic changes in climatic conditions that supplement the biotic and abiotic stresses pose severe threat to the sustainable rice production and have made it a difficult task for rice molecular breeders to enhance production and productivity under these stress factors. The main focus of rice molecular breeders is to understand the fundamentals of molecular pathways involved in complex agronomic traits to increase the yield. The availability of complete rice genome sequence and recent improvements in rice genomics research has made it possible to detect and map accurately a large number of genes by using linkage to DNA markers. Linkage mapping is an effective approach to identify the genetic markers which are co-segregating with target traits within the family. The ideas of genetic diversity, quantitative trait locus（QTL） mapping, and marker-assisted selection（MAS） are evolving into more efficient concepts of linkage disequilibrium（LD） also called association mapping and genomic selection（GS）, respectively. The use of cost-effective DNA markers derived from the fine mapped position of the genes for important agronomic traits will provide opportunities for breeders to develop high-yielding, stress-resistant, and better quality rice cultivars. Here we focus on the progress of molecular marker technologies, their application in genetic mapping and evolution of association mapping techniques in rice.

A Forensic Method for Efficient File Extraction in HDFS Based on Three-Level Mapping

The large scale and distribution of cloud computing storage have become the major challenges in cloud forensics for file extraction. Current disk forensic methods do not adapt to cloud computing well and the forensic research on distributed file system is inadequate. To address the forensic problems, this paper uses the Hadoop distributed file system （HDFS） as a case study and proposes a forensic method for efficient file extraction based on three-level （3L） mapping. First, HDFS is analyzed from overall architecture to local file system. Second, the 3L mapping of an HDFS file from HDFS namespace to data blocks on local file system is established and a recovery method for deleted files based on 3L mapping is presented. Third, a multi-node Hadoop framework via Xen virtualization platform is set up to test the performance of the method. The results indicate that the proposed method could succeed in efficient location of large files stored across data nodes, make selective image of disk data and get high recovery rate of deleted files.

Characterization and Fine Mapping of a Necrotic Leaf Mutant in Maize(Zea mays L.)

Maize（Zea mays L.） is a commercially important crop.Its yield can be reduced by mutations in biosynthetic and degradative pathways that cause death.In this paper,we describe the necrotic leaf（nec-t） mutant,which was obtained from an inbred line,81647.The nec-t mutant plants had yellow leaves with necrotic spots,reduced chlorophyll content,and the etiolated seedlings died under normal growth conditions.Transmission electron microscopy revealed scattered thylakoids,and reduced numbers of grana lamellae and chloroplasts per cell.Histochemical staining suggested that spot formation of nec-t leaves might be due to cell death.Genetic analysis showed that necrosis was caused by the mutation of a recessive locus.Using simple sequence repeat markers,the Nec-t gene was mapped between mmc0111 and bnlg2277 on the short arm of chromosome 2.A total of 1287 individuals with the mutant phenotype from a F_2 population were used for physical mapping.The Nec-t gene was located between markers T31 and H8 within a physical region of 131.7 kb.