Vol 17, No 1 (2019)

Genetic basis of ecosystems evolution

The state of art and prospects for development of symbiogenetics

Provorov N.A., Tikhonovich I.A.


The modern stage of development of symbiogenetics, a biological discipline that addresses the formation of super-species genetic systems, is associated with the study of molecular mechanisms and environmental consequences of combining the hereditary factors of prokaryotes and eukaryotes into functionally integrated symbiogenomes, which, as partners lose their ability to autonomous existence, are transformed into structurally integrated hologenomes. The loss by intracellular symbionts of eukaryotes of their genetic individuality, determined by the ability to independently maintain and express the genome, representing a key step in symbiogenesis which results in the transformation of bacteria into cellular organelles. Genetic reconstruction of symbiogenesis provides the broad prospects for its artificial reproduction aimed at the synthesis of new organisms and biosystems possessing the predetermined sets of practically significant features.

Ecological genetics. 2019;17(1):5-10
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Ecological and genetic bases for construction of highly effective nitrogen-fixing microbe-plant symbioses

Provorov N.A., Onishchuk O.P.


Expression of quantitative traits characterizing the N2-fixing symbiosis of nodule bacteria and leguminous plants is associated with operation of the evolutionary derived polygenic systems controlling the symbiotic efficiency (SE) (impact of inoculation on the plant productivity) and nodulation competitiveness (NC) (formation of nodules by rhizobia under mixed inoculation). Optimization of balance between positive and negative symbiotic regulators aimed at an increase of nitrogenase activity and at a complete allocation of its products into the plant metabolism provides the generation of rhizobia strains with high SE and NC. Inactivation of the negative symbiotic regulators often results in a decreased survival of rhizobia under the edaphic stresses but is responsible for a balanced increase of plant biomass and N accumulation. Improvement of symbiotic activity is to be based on the complementary interactions of microorganisms with the genetically engineered plant cultivars which are able for selection from soil of actively fi xing N2 rhizobia strains and for their preferential multiplication in nodules. Construction of highly effective microbe-plant systems should be based on modifications of mechanisms controlling symbiosis development from the plant and bacterial sides providing the maintenance of N2-fixing zone in nodules and synthesis of NCR proteins activating the bacteroid differentiation.

Ecological genetics. 2019;17(1):11-18
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Endophytic microorganisms in fundamental research and agriculture

Vasileva E.N., Akhtemova G.A., Zhukov V.A., Tikhonovich I.A.


The ubiquity of endophytic microorganisms is an accepted fact nowadays and the possibility of using it in agriculture keeps attracting attention of scientific community. In contrast to rhizospheric (living on root surface) and phyllospheric (colonizing aerial parts of plants) members of plant-microbial interactions endophytes are able to establish closer relationships with host-plant, in some cases strongly influencing its phenotype, bringing benefits. However, these microorganisms do not form any specific structures like nodules in case of symbiosis between legumes and rhizobium bacteria. Having a great amount of functions including phytohormone level modulation, vitamins production and nutrient supply improving, endophytes could serve as a basis for biofertilizer, which could potentially minimize the necessity of mineral fertilizers, thus reducing the negative impact of the latter on soil fertility, biodiversity and human health. Our main aim here is to highlight the question of functional significance of endophytes and endophytic bacteria in particular, as well as the way of its application in agriculture and to identify key points in understanding biology of these organisms. In this review we will consider such aspects of plant-endophytic symbiosis as biodiversity of legume and non-legume endophytes, ecology of endophytes and some ways which are commonly in use by studying these microorganisms.

Ecological genetics. 2019;17(1):19-32
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The role of universal regulators of plant growth and development the DELLA proteins in the control of symbiosis

Dolgikh A.V., Dolgikh E.A.


The regulators of the gibberellin response, the DELLA proteins, are universal participants of signaling pathways that coordinate the processes of plant growth and development. This regulation is provided by the integration of external effect, as well as internal signals, such as a level of phytohormones and secondary messengers. Since DELLA proteins are extremely sensitive to increasing or decreasing of the gibberellic acid (GA) endogenous level, their direct interaction with transcription factors modulates the activity of the latter, and, consequently, the level of expression of target genes in response to external signals causing changes in the level of GA. However, the molecular mechanisms of the effect of DELLA proteins on the development of symbiosis remain poorly understood. The review analyzes classical and modern data on the functioning of DELLA proteins in plants.

Ecological genetics. 2019;17(1):33-41
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The genetic diversity of microsymbionts from Thermopsis lanceolata growing in Mongolia

Karlov D.S., Sazanova A.L., Kuznetsova I.G., Safronova V.I., Tikhomirova N.Y., Popova Z.P., Osledkin Y.S., Verkhozina A.V., Belimov A.A.


For the first time, bacteria were isolated and identified from the root nodules of a wild-growing medicinal legume plant Thermopsis lanceolata, originated from Mongolia. The taxonomic position of 14 isolates obtained was determined using of sequencing of the 16S rRNA (rrs) and atpD genes. It was shown a significant biodiversity of the isolates from T. lanceolata, which belonged to three genera of the order Rhizobiales: Phyllobacterium (family Phyllobacteriaceae), Rhizobium (family Rhizobiaceae) and Bosea (family Bradyrhizobiaceae). Six isolates belonged to the species Phyllobacterium zundukense and Phyllobacterium trifolii (100 и 99,9% rrs similarity with the type strains P. zundukense Tri-48T and P. trifolii PETP02T, respectivelly), three isolates were identified as Rhizobium anhuiense (99,8% rrs similarity with the type strain R. anhuiense CCBAU 23252T). Two slow-growing isolates of the genus Bosea Tla-534 and Tla-545 may potentially belong to new species, since their rrs-similarity to the closest type strains B. massiliensis LMG 26221T, B. lathyri LMG 26379T and B. vaviloviae Vaf18T was 98,5-99,0%. Non-rhizobial strains were not isolated. The isolation and future investigation of the rhizobial microsymbionts of the valuable medicinal legume Thermopsis lanceolata is one of the necessary prerequisites for its industrial cultivation.

Ecological genetics. 2019;17(1):43-51
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Analysis of alternative splicing events in the root tips and nodules of Pisum sativum L

Zorin E.A., Kulaeva O.A., Afonin A.M., Zhukov V.A., Tikhonovich I.A.


Background. Legumes establish symbioses with nitrogen-fixing bacteria from the Rhizobium group. In exchange for nutrients, bacteria provide fixed nitrogen needed to support plant growth. At the moment, information about the involvement of alternative splicing (AS) in the establishment and maintenance this symbiotic relationships is almost absent, but, as it is a powerful mechanism for the regulation of proteome diversity of the cell, it therefore may participate in cellular response to microsymbionts.

Materials and methods. Alternative splicing was analyzed using the assembly of “supertranscripts” and alignment of the reads from nodules and root tips to this reference. Target genes expression levels was estimated in tips of non-inoculated roots, and in nodules (2, 4, and 6 weeks post inoculation) with use of RT-qPCR.

Results.In this study, the analysis of AS events in the nodules and root tips of the pea was carried out. The presence of isoforms of four pea genes (PsSIP1, PsIGN, PsWRKY40, PsPR-10) was confirmed and their expression level was estimated.

Conclusion. Pea nodules were shown to be more enriched with AS events compared to root tips. Among the functional groups of genes that demonstrate AS events, one of the most enriched functional groups is the pathogens stress response. Intron retention probably leads to degradation of the transcript via NMD-system or to change of the protein function, that modulates the activity of genes in nodules.

Ecological genetics. 2019;17(1):53-63
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Histological and ultrastructural nodule organization of the pea (Pisum sativum) mutant sgefix–-5 in the Sym33 gene encoding the transcription factor PsCYCLOPS/PsIPD3

Tsyganova A.V., Ivanova K.A., Tsyganov V.E.


Background. The transcription factor CYCLOPS/IPD3 is a key activator of the organogenesis of symbiotic nodules. Its participation in the development of infection threads and symbiosomes is also shown. In pea, three mutant alleles were identified for this gene (sym33-1sym33-3). The phenotypic manifestations of the sym33-3 allele of the SGEFix¯-2 mutant, characterized by a “leaky” phenotype (the formation of two types of nodules: white and pinkish) were the most studied. The sym33-2 allele in the mutant SGEFix¯-5 was described as a strong allele, however, its phenotypic manifestations have not been studied in detail.

Materials and methods. In this study, the histological and ultrastructural nodule organization of the SGEFix¯-5 mutant was analyzed using confocal laser scanning microscopy and transmission electron microscopy.

Results. In the nodules “locked” infection threads were observed, from which no bacteria release into the cytoplasm of the plant cell occurs. In this case, in some infection threads, bacteria were degraded, which may indicate the activation of strong defense reactions in the nodules of the SGEFix¯-5 mutant.

Conclusions. The sym33-2 allele in the mutant SGEFix¯-5 is a strong allele, which triggers the severe defense reactions, when rhizobia are already perceived as pathogens in infection threads.

Ecological genetics. 2019;17(1):65-70
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Influence of mutation in pea (Pisum sativum L.) cdt (cadmium tolerance) gene on histological and ultrastructural nodule organization

Tsyganova A.V., Seliverstova E.V., Tsyganov V.E.


Background. A comparative analysis out of the structural organization of the symbiotic nodules of the pea initial line SGE and the mutant line SGECdt, characterized by increased tolerance to cadmium and increased its accumulation, was carried out.

Materials and methods.Nodules of initial line SGE and mutant SGECdt were analyzed using light and transmission electron microscopy.

Results. The non-treated nodules of SGE and SGECdt were characterized by a similar histological and ultrastructural organization. In the nodules of SGE exposed to 100 µM CdCl2 in infected cells, the following abnormalities were observed: expansion of the peribacteroid space, destruction of the symbiosome membrane, fusion of symbiosomes and, as a result, the formation of symbiosomes containing several bacteroids. In the nodules of SGECdt, infected cells did not undergo pronounced changes. In the nodules of SGE exposed to 1 mM CdCl2, at the base of the nodule, senescent infected cells with completely destroyed cytoplasm and degrading bacteroids appeared. Also there were present cells in which the contents of symbiosomes were lysing, and only the “ghosts” of the bacteroids remained in them. In SGECdt, in some infected cells, abnormalities were manifested in an increase in the peribacteroid space, partial destruction of symbiosome membranes, fusion of symbiosomes, and release of bacteroids into the vacuole.

Conclusions. The tolerance of pea nodules to cadmium can be significantly increased due to a single recessive cdt mutation.

Ecological genetics. 2019;17(1):71-80
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Molecular genetic mechanisms of sugar transport in plants in the absence and during arbuscular mycoryza development

Yurkov A.P., Kryukov A.A., Gorbunova A.O., Afonin A.M., Kirpichnikova A.A., Dobryakova K.S., Machs E.M., Shishova M.F.


The review is aimed to analyze molecular mechanisms of carbohydrate transport during the formation of arbuscular mycorrhiza (AM), a widespread symbiosis of plants with Glomeromycotina subdivision fungi. Due to AM-symbiosis, plants receive microelements, mainly phosphorus, and fungi are supplied by products of carbon assimilation. The study of sugar transport mechanisms in plants as well as between plants and symbiont is methodologically difficult because of the obligatory status of AM fungi. The mechanisms of carbohydrate transport in leaf and root cells are concerned, particular interest is paid to transporters, specific to AM structures. Several resumptive schemes are designed. SWEET family of transporters (Sugars Will Eventually be Exported Transporters), including AM-specific uniporters are reviewed. We summarize results on expression of genes encoding transporter in cells of plants without AM, in AM-plant cells with arbuscules and AM-plant cells without arbuscules. The data on genes of MST proteins family (Monosaccharide Transporters) participating in direct transport of sugars from the soil to the foliar mycelium of AM fungi are considered.

Ecological genetics. 2019;17(1):81-99
pages 81-99 views

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