Metabolic engineering of a diazotrophic bacterium improves ammonium release and biofertilization of plants and microalgae

The biological nitrogen fixation carried out by some Bacteria and Archaea is one of the most attractive alternatives to synthetic nitrogen fertilizers. However, with the exception of the symbiotic rhizobia-legumes system, progress towards a more extensive realization of this goal has been slow. In this study we manipulated the endogenous regulation of both nitrogen fixation and assimilation in the aerobic bacterium Azotobacter vinelandii. Substituting an exogenously inducible promoter for the native promoter of glutamine synthetase produced conditional lethal mutant strains unable to grow diazotrophically in the absence of the inducer. This mutant phenotype could be reverted in a double mutant strain bearing a deletion in the nifL gene that resulted in constitutive expression of nif genes and increased production of ammonium. Under GS non-inducing conditions both the single and the double mutant strains consistently released very high levels of ammonium (>20 mM) into the growth medium. The double mutant strain grew and excreted high levels of ammonium under a wider range of concentrations of the inducer than the single mutant strain. Induced mutant cells could be loaded with glutamine synthetase at different levels, which resulted in different patterns of extracellular ammonium accumulation afterwards. Inoculation of the engineered bacteria into a microalgal culture in the absence of sources of C and N other than N₂ and CO₂ from the air, resulted in a strong proliferation of microalgae that was suppressed upon addition of the inducer. Both single and double mutant strains also promoted growth of cucumber plants in the absence of added N-fertilizer, while this property was only marginal in the parental strain. This study provides a simple synthetic genetic circuit that might inspire engineering of optimized inoculants that efficiently channel N₂ from the air into crops.     

Evolutionary relationships of eukaryotic kingdoms

The evolutionary relationships of four eukaryotic kingdoms—Animalia, Plantae, Fungi, and Protista—remain unclear. In particular, statistical support for the closeness of animals to fungi rather than to plants is lacking, and a preferred branching order of these and other eukaryotic lineages is still controversial even though molecular sequences from diverse eukaryotic taxa have been analyzed. We report a statistical analysis of 214 sequences of nuclear small-subunit ribosomal RNA (srRNA) gene undertaken to clarify these evolutionary relationships. We have considered the variability of substitution rates and the nonindependence of nucleotide substitution across sites in the srRNA gene in testing alternative hypotheses regarding the branching patterns of eukaryote phylogeny. We find that the rates of evolution among sites in the srRNA sequences vary substantially and are approximately gamma distributed with size and shape parameter equal to 0.76. Our results suggest that (1) the animals and true fungi are indeed closer to each other than to any other crown group in the eukaryote tree, (2) red algae are the closest relatives of animals, true fungi, and green plants, and (3) the heterokonts and alveolates probably evolved prior to the divergence of red algae and animal-fungus-green-plant lineages. Furthermore, our analyses indicate that the branching order of the eukaryotic lineages that diverged prior to the evolution of alveolates may be generally difficult to resolve with the srRNA sequence data.     

Identification and localization of calreticulin in plant cells

Summary In the present study we have investigated the presence and distribution of calreticulin in plant protoplasts. Calreticulin was purified from plant homogenates using a selective ammonium sulfate precipitation procedure developed for the purification of mammalian calreticulins and shown to bind calcium in⁴⁵Ca²⁺ overlay assays. The protein was localized to plant cell endoplasmic reticulum by the indirect immunofluorescence staining of protoplasts with anti-calreticulin antibodies. No calreticulin was observed within large vacuoles. We conclude that calreticulin is present in the endoplasmic reticulum of plant cells, where, by analogy to the mammalian endoplasmic reticulum, it may play a major role in Ca²⁺ binding and storage.Abbreviations ER endoplasmic reticulum - SR sarcoplasmic reticulum - SDS-PAGE sodium dodecyl sulfate-polyacrylamide gel electrophoresis - PBS phosphate-buffered saline     

Induction of high polyploidy in Phaseolus cell cultures by the protein kinase inhibitor,K-252a

Summary Somatic polyploidy of species-specific and tissue-specific degrees occurs in almost all plant species studied so far, but nearly nothing is known about the control mechanisms switching the mitotic cycle to an endoreduplication cycle. In order to search for a possible role of the cdc2 kinase, cell suspension cultures of the Runner bean, Phaseolus coccineus (Leguminosae) were treated with K-252a, an inhibitor of protein kinase activity. The treatment resulted in continuous cell cycles without mitosis, and hence induced polyploidy levels up to 2048C. It is, therefore, suggested that phosphorylation of a protein kinase, probably of the cell cycle-important p34^cdc2 type, is involved in the control of endoreduplication.     

Crop responses to CO2 enrichment

Carbon dioxide is rising in the global atmosphere, and this increase can be expected to continue into the foreseeable future. This compound is an essential input to plant life. Crop function is affected across all scales from biochemical to agro-ecosystem. An array of methods (leaf cuvettes, field chambers, free-air release systems) are available for experimental studies of CO₂ effects. Carbon dioxide enrichment of the air in which crops grow usually stimulates their growth and yield. Plant structure and physiology are markedly altered. Interactions between CO₂ and environmental factors that influence plants are known to occur. Implications for crop growth and yield are enormous. Strategies designed to assure future global food security must include a consideration of crop responses to elevated atmospheric CO₂. Future research should include these targets: search for new insights, development of new techniques, construction of better simulation models, investigation of belowground processes, study of interactions, and the elimination of major discrepancies in the scientific knowledge base.     

Effect of plant growth and addition of plant residues on the phosphatase activity in soil

Summary The phosphatase activity of the soil amended with roots and tops of clover (Trifolium repens) plant material (0.1% by weight) remained essentially constant in the absence of growing plants but changed considerably in the presence of plants (Avena sativa) grown for 10 weeks. There was a significant relationship between the phosphatase activity and organic and inorganic P in the soil solution only in the presence of growing plants. The differences in phosphatase activity between roots and tops amended soil were attributed to total C as well as differences in the degree of availability of C added through plant materials. This may also apply to the carpet grass (Axonopus affinis) amended soil.     

Evolution of incompatibility systems in plants: Complementarity and the mating locus in flowering plants and fungi

Summary The restriction of sexual pairing by a specificity gene is considered to be an ancient development in the plant kingdom. The diversity and general parallelism of incompatibility systems seen amongst the phyla at the present time can be rationalized in terms of the association of various derived forms of the ancestral specificity unit with differing spectra of accessory factors controlling sexual physiology in the different phyla. Sexual morphogenesis has become divided into distinct phases under the control of complementary genes. These phases are initiated by a regulatory system of Co-ordinator genes which control the order in which groups of morphogenetic genes are expressed during development. The entire sexual cycle will be completed only if all the complementary groups are activated in the appropriate sequence. The present article discusses essential features of the evolution of the breeding locus in different phyla. These features are consistent in themselves with the present data and are not dependent on the proposed ancient origin of the specificity gene.The above hypothesis throws light on the (1) evolution of the complex mating loci in flowering plants and fungi; (2) evolution of complementary incompatibility and heteromorphic incompatibility in flowering plants; (3) anomalous cross-compatibility behaviour of mutants in the fungus Schizophyllum commune; (4) nature of homothallism in higher fungi; (5) mode of origin of new functional self-incompatibility alleles; and (6) homogenic and heterogenic incompatibility.     

Diversity and significance of late cretaceous permineralized plant remains from Hokkaido,Japan

Middle to Late Cretaceous permineralized plants hitherto described from Hokkaido, Japan are summarized. The fossil flora comprises fungi, ferns, gymnosperms and angiosperms. Many modern fern families have been recognized including Anemiaceae, Cyatheaceae, Dennstaedtiaceae, Gleicheniaceae Loxsomaceae, Lygodiaceae and Matoniaceae. Gymnosperms are most abundant in the flora. Some recently-found materials are tentatively introduced with brief comments emphasizing their morphological and taxonomical significance. A bisporangiate flower ofCycadeoidella japonica Ogura shows fine internal anatomy and provides evidence that the cycadeoidalean ovule was a cupulate, unitegmic structure. Vascular tracheids in the synangial wall support the evolution of cycadeoidalean synangia from Paleozoic seed-fern synangia. A new gymnosperm female fructification has a thick envelope comparable to an angiosperm carpel around a large seed. The angiosperms contain various morphologies that require further extensive study.     

Regulated Changes in the Acetylation of α-Tubulin on Lys40 during Growth and Organ Development in Fast Plants,Brassica rapa L.

Recently, we confirmed the widespread occurrence of α-tubulin acetylation on Lys⁴⁰ in angiosperms. In the present study, we found that α-tubulin acetylation is regulated in a growth stage- and organ development-dependent manner in the rapid cycling Brassica rapa, also known as Fast Plants. Organ distribution analysis showed that the proportion of acetylated α-tubulin is high in the cotyledons of young plants and in the true leaves and flowers of mature plants. A correlation between the increase in the levels of α-tubulin acetylation and the maturation of true leaves was observed. In the mature leaves, the acetylated α-tubulin showed an uneven distribution pattern, and the cells in the region of the leaf margins contained a high proportion of acetylated α-tubulin. These results indicate that α-tubulin acetylation is dynamically regulated in plant organs during development, and that it might play an important role in microtubule functioning throughout the angiosperm's life cycle.     

《国家重点保护野生植物名录》调整的必要性、原则和程序

我国是世界上植物多样性最丰富的国家之一, 1999年发布的《国家重点保护野生植物名录》(下称《名录》(第一批))明确了国家重点保护野生植物的范围, 为依法强化保护、规范无序开发利用、提高公众保护意识奠定了基础。20多年来, 我国野生植物多样性保护形势发生了很大变化, 需要对《名录》进行调整。2018年, 国家林业和草原局、农业农村部启动《名录》调整工作, 物种的遴选遵循了5条基本原则和4条补充性原则, 这些原则主要涉及中国珍稀濒危物种, 具有重要经济、文化、科研、生态等价值物种的入选以及部分物种的排除。经国务院批准, 2021年9月7日, 国家林业和草原局、农业农村部发布了调整后的《名录》, 包括真菌类、藻类、苔藓、石松类和蕨类植物、裸子植物和被子植物, 共计约1,101种(455种和40类)野生植物列入其中。本文简要介绍了《名录》调整的必要性、原则和程序及调整后的情况。