Screening of candidate genes and fine mapping of drought tolerance quantitative trait loci on chromosome 4 in rice (Oryza sativa L.) under drought stress.

Due to severe water resource shortage, genetics of and breeding for DT (drought tolerance) in rice (Oryza sativa L.) have become one of the hot research topics. Identification of grain yield QTLs (quantitative trait loci) directly related to the DT trait of rice can provide useful information for breeding new drought-resistant and water-saving rice varieties via marker-assisted selection. A population of 105 advanced BILs (backcross introgression lines) derived from a cross between Zhenshan97B and IRAT109 in Zhenshan97B background were grown under drought stress in a field experiment and phenotypic traits were investigated. The results showed that in the target interval of RM273-RM255 on chromosome 4, three main-effect QTLs related to panicle length, panicle number, and spikelet number per panicle were identified (LOD [logarithm of the odds] > 2.0). The panicle length-related QTL had two loci located in the neighboring intervals of RM17308-RM17305 and RM17349-RM17190, which explained 18.80% and 20.42%, respectively, of the phenotypic variation, while the panicle number-related QTL was identified in the interval of RM1354-RM17308, explaining 11.47% of the phenotypic variation. As far as the spikelet number per panicle-related QTL was concerned, it was found to be located in the interval of RM17308-RM17305, which explained 28.08% of the phenotypic variation. Using the online Plant-GE query system, a total of 13 matched ESTs (expressed sequence tags) were found in the target region, and of the 13 ESTs, 12 had corresponding predicted genes. For instance, the two ESTs CB096766 and CA765747 were corresponded to the same predicted gene LOC_Os04g46370, while the other four ESTs, CA754286, CB000011, CX056247, and CX056240, were corresponded to the same predicted gene LOC_Os04g46390.

Bacillus zhanjiangensis sp. nov., isolated from an oyster in South China Sea.

A novel Gram-stain-positive, motile, catalase- and oxidase-positive, endospore-forming, aerobic, rod-shaped bacterium, designated strain JSM 099021(T), was isolated from an oyster collected from Naozhou Island in the South China Sea. Growth occurred with 0-15% (w/v) NaCl (optimum 2-4%) and at pH 6.0-10.0 (optimum pH 7.5) and at 10-45°C (optimum 30-35°C). meso-Diaminopimelic acid was present in the cell-wall peptidoglycan. The predominant respiratory quinone was menaquinone 7 (MK-7) and the major polar lipids consisted of diphosphatidylglycerol, phosphatidylethanolamine and phosphatidylglycerol. The major cellular fatty acids were anteiso-C15:0, anteiso-C17:0, iso-C15:0 and iso-C16:0. The genomic DNA G + C content was 39.5 mol%. A phylogenetic analysis based on 16S rRNA gene sequences indicated that strain JSM 099021(T) belongs to the genus Bacillus, and was most closely related to the type strains of Bacillus halmapalus (sequence similarity 99.0%), Bacillus horikoshii (98.4%) and Bacillus cohnii (98.0%). The combination of phylogenetic analysis, DNA-DNA hybridization, phenotypic characteristics and chemotaxonomic data supported the proposal that strain JSM 099021(T) represents a new species of the genus Bacillus, for which the name Bacillus zhanjiangensis sp. nov. is proposed. The type strain was JSM 099021(T) (=DSM 23010(T) = KCTC 13713(T)).

Correlation and quantitative trait loci analyses of total chlorophyll content and photosynthetic rate of rice (Oryza sativa) under water stress and well-watered conditions.

In order to explore the relevant molecular genetic mechanisms of photosynthetic rate (PR) and chlorophyll content (CC) in rice (Oryza sativa L.), we conducted a series of related experiments using a population of recombinant inbred lines (Zhenshan97B x IRAT109). We found a significant correlation between CC and PR (R= 0.19**) in well-watered conditions, but no significant correlation during water stress (r= 0.08). We detected 13 main quantitative trait loci (QTLs) located on chromosomes 1, 2, 3, 4, 5, 6, and 10, which were associated with CC, including six QTLs located on chromosomes 1, 2, 3, 4, and 5 during water stress, and seven QTLs located on chromosomes 2, 3, 4, 6, and 10 in well-watered conditions. These QTLs explained 47.39% of phenotypic variation during water stress and 56.19% in well-watered conditions. We detected four main QTLs associated with PR; three of them (qPR2, qPR10, qPR11) were located on chromosomes 2, 10, and 11 during water stress, and one (qPR10) was located on chromosome 10 in well-watered conditions. These QTLs explained 34.37% and 18.41% of the phenotypic variation in water stress and well-watered conditions, respectively. In total, CC was largely controlled by main QTLs, and PR was mainly controlled by epistatic QTL pairs.

Dissection of additive, epistatic effect and Q x E interaction of quantitative trait loci influencing stigma exsertion under water stress in rice.

Four flowering related traits, spikelet number per panicle (SNP), percentage of single exserted stigma (PSES), dual exserted stigma (PDES) and total exserted stigma (PES) of a RI population with 185 lines under water stress and non-stress conditions for 2 years, were investigated in a drought tolerance screening facility. ANOVA results showed high significance between years, lines, and water stress treatments, together with interactions among them in pairs. Highest phenotypic correlation was found between PSES and PES (r = 0.9752***), followed by PDES and PES (r = 0.7150***), and PSES and PDES (r = 0.5424***). Based on a linkage map of 203 SSR markers, six main effect QTLs were detected for SNP and three or four main effect QTLs were associated with PSES, PDES and PES under stress or non-stress conditions. There were one to nine pairs of epistatic QTLs influencing SNP and stigma exsertion. The contribution rates of additive and epistatic effects seemed to be in a low magnitude for most cases (0.76%-9.92%) while a few QTLs or QTL pairs explained more than 10% of total variance. Some main effect QTL and epistasis were commonly detected among PSES, PDES and PES, explaining the high positive correlation between them. Few QTLs were detected under both water stress and non-stress condition, implying that drought had severe impact on the genetic behaviors of both spikelet number and stigma exsertion.