Nitric oxide (NO) plays important roles in diverse physiological processes in plants. NO can provoke both beneficial and harmful effects, which depend on the concentration and location of NO in plant cells. This review is focused on NO synthesis and the functions of NO in plant responses to abiotic environmental stresses. Abiotic stresses mostly induce NO production in plants. NO alleviates the harmfulness of reactive oxygen species, and reacts with other target molecules, and regulates the expression of stress responsive genes under various stress conditions.

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The chloroplast genome originated from photosynthetic organisms and has retained the core genes that mainly encode components of photosynthesis. However, the causes of variations in chloroplast genome size in seed plants have only been thoroughly analyzed within small subsets of spermatophytes. In this study, we conducted the first comparative analysis on a large scale to examine the relationship between sequence characteristics and genome size in 272 seed plants based on cross-species and phylogenetic signal analysis. Our results showed that inverted repeat regions, large or small single copies, intergenic regions, and gene number can be attributed to the variations in chloroplast genome size among closely related species. However, chloroplast gene length underwent evolution affecting chloroplast genome size in seed plants irrespective of whether phylogenetic information was incorporated. Among chloroplast genes, atpA, accD and ycf1 account for 13% of the variation in genome size, and the average Ka/Ks values of homologous pairs of the three genes are larger than 1. The relationship between chloroplast genome size and gene length might be affected by selection during the evolution of spermatophytes. The variation in chloroplast genome size may influence energy generation and ecological strategy in seed plants.

A four-carbon dicarboxylic acid L-malate has recently attracted attention due to its potential applications in the fields of medicine and agriculture. In this study, Escherichia coli W3110 was engineered and optimized for L-malate production via one-step L-malate synthesis pathway. First, deletion of the genes encoding lactate dehydrogenase (ldhA), pyruvate oxidase (poxB), pyruvate formate lyase (pflB), phosphotransacetylase (pta), and acetate kinase A (ackA) in pta-ackA pathway led to accumulate 20.9 g/L pyruvate. Then, overexpression of NADP -dependent malic enzyme C490S mutant in this multi-deletion mutant resulted in the direct conversion of pyruvate into L-malate (3.62 g/L). Next, deletion of the genes responsible for succinate biosynthesis further enhanced L-malate production up to 7.78 g/L. Finally, L-malate production was elevated to 21.65 g/L with the L-malate yield to 0.36 g/g in a 5 L bioreactor by overexpressing the pos5 gene encoding NADH kinase in the engineered E. coli F0931 strain. This study demonstrates the potential utility of one-step pathway for efficient L-malate production. Biotechnol. Bioeng. 2017;114: 656-664. © 2016 Wiley Periodicals, Inc.

BackgroundSchizochytrium limacinum SR21 is a potential industrial strain for docosahexaenoic acid (DHA) production that contains more than 30–40 % DHA among its total fatty acids.MethodsTo resolve the DHA biosynthesis mechanism and improve DHA production at a systematic level, a genomescale metabolic model (GSMM), named iCY1170_DHA, which contains 1769 reactions, 1659 metabolites, and 1170 genes, was reconstructed.ResultsBased on genome annotation results and literature reports, a new DHA synthesis pathway based on a polyketide synthase (PKS) system was detected in S. limacinum. Similarly to conventional fatty acid synthesis, the biosynthesis of DHA via PKS requires abundant acetyl-CoA and NADPH. The in silico addition of malate and citrate led to increases of 24.5 % and 37.1 % in DHA production, respectively. Moreover, based on the results predicted by the model, six amino acids were shown to improve DHA production by experiment. Finally, 30 genes were identified as potential targets for DHA over-production using a Minimization of Metabolic Adjustment algorithm.ConclusionsThe reconstructed GSMM, iCY1170_DHA, could be used to elucidate the mechanism by which DHA is synthesized in S. limacinum and predict the requirements of abundant acetyl-CoA and NADPH for DHA production as well as the enhanced yields achieved via supplementation with six amino acids, malate, and citrate.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-2042-y) contains supplementary material, which is available to authorized users.

BackgroundWild rice (Oryza rufipogon) constitutes a primary gene source for rice breed improvement. Chromosome segment substitution line (CSSL) for O. rufipogon is a powerful tool for fine mapping of quantitative traits, new gene discovery, and marker-assisted breeding. Thus, they provide a basis for a wide range of genomic and genetic studies.ResultsIn this study, a set of 198 CSSLs were developed from a cross between recurrent parent indica var. 9311 and an O. rufipogon donor parent; these were then genotyped using 313 polymorphic SSR markers evenly distributed across the 12 rice chromosomes. On average, each CSSL carried 2.16 introgressed segments, and the genetic distance of each segment was about 6 cM. The segments collectively covered 84.9 % of the wild rice genome. Based on these CSSLs, 25 QTLs involved in 10 agronomic traits were identified. Seven CSSLs were subjected to a whole-genome single nucleotide polymorphism chip assay and two QTLs, qSH4-1 and qDTH10-1, detected. In addition, a new QTL associated with the heading date was detected in a 78-Kb region on chromosome 10, thus proving the ability of these CSSLs to identify new QTLs and genes.ConclusionsThe newly developed CSSL population proved a useful tool for both gene identification and whole-genome research of wild rice. These CSSL materials will provide a foundation for rice variety improvement.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-2987-5) contains supplementary material, which is available to authorized users.

Previous studies have indicated that China is one of the domestication centres of Asian cultivated rice (Oryza sativa), and common wild rice (O. rufipogon) is the progenitor of O. sativa. However, the number of domestication times and the geographic origin of Asian cultivated rice in China are still under debate. In this study, 100 accessions of Asian cultivated rice and 111 accessions of common wild rice in China were selected to examine the relationship between O. sativa and O. rufipogon and thereby infer the domestication and evolution of O. sativa in China through sequence analyses of six gene regions, trnC-ycf6 in chloroplast genomes, cox3 in mitochondrial genomes and ITS, Ehd1, Waxy, Hd1 in nuclear genomes. The results indicated that the two subspecies of O. sativa (indica and japonica) were domesticated independently from different populations of O. rufipogon with gene flow occurring later from japonica to indica; Southern China was the genetic diversity centre of O. rufipogon, and the Pearl River basin near the Tropic of Cancer was the domestication centre of O. sativa in China.

Genomes carry millions of noncoding variants, and identifying the tiny fraction with functional consequences is a major challenge for genomics. We assessed the role of selection on long noncoding RNAs (lncRNAs) for domestication-related changes in rice grains. Among 3363 lncRNA transcripts identified in early developing panicles, 95% of those with differential expression (329 lncRNAs) between Oryza sativa ssp. japonica and wild rice were significantly down-regulated in the domestication event. Joint genome and transcriptome analyses reveal that directional selection on lncRNAs altered the expression of energy metabolism genes during domestication. Transgenic experiments and population analyses with three focal lncRNAs illustrate that selection on these loci led to increased starch content and grain weight. Together, our findings indicate that genome-wide selection for lncRNA down-regulation was an important mechanism for the emergence of rice domestication traits.