Intensive exchange of nutrients is a crucial part of the complex interaction between a host plant and fungi within arbuscular mycorrhizal (AM) symbiosis. For the first time, the present study demonstrates how inoculation with AMF Rhizophagus irregularis affects the pea (Pisum sativum L.) root metabolism at key stages of plant development. These correspond to days 21 (vegetation), 42 (flowering initiation), and 56 (fruiting-green pod). Metabolome profiling was carried out by means of a state-of-the-art GC-MS technique. The content shifts revealed include lipophilic compounds, sugars, carboxylates, and amino acids. The metabolic alterations were principally dependent on the stage of plant development but were also affected by the development of AM fungi, a fact which highlights interaction between symbiotic partners. The comparison of the present data with the results of leaf metabolome profiling earlier obtained did not reveal common signatures of metabolic response to mycorrhization in leaves and roots. We supposed that the feedback for the development and symbiotic interaction on the part of the supraorganismic system (root + AM fungi) was the cause of the difference between the metabolic profile shift in leaf and root cells that our examination revealed. New investigations are required to expand our knowledge of metabolome plasticity of the whole organism and/or system of organisms, and such results might be put to use for the intensification of sustainable agriculture.

Plants are continuously exposed to various biotic and abiotic factors that may trigger cascade reactions aimed at maintaining homeostasis. One of the most important components of plant protection from biotic factors is the synthesis of antimicrobial peptides (AMPs). AMPs are a large group of peptides present in insects, animals and plants. Plant innate immunity is provided by AMPs from different families that are categorized according to sequence similarity, the number and order of amino acid residues, and the tertiary structure of the mature peptide. AMPs may also participate in plant response to abiotic stresses such as high salinity, drought, high or low temperature, and heavy metals. In nitrogen-fixing nodules of some members of the Fabaceae family, AMP-like molecules named NCR peptides promote the differentiation of the symbiotic bacteria into bacteroids. Thus, AMPs are used by plants for fine tuning their responses to biotic and abiotic factors alike.

The garden pea (Pisum sativum L.), like most members of Fabaceae family, is capable of forming symbioses with beneficial soil microorganisms such as nodule bacteria (rhizobia), arbuscular mycorrhizal (AM) fungi and plant growth promoting bacteria (PGPB). The autoregulation of nodulation (AON) system is known to play an important role in controlling both the number of nodules and the level of root colonization by AM via root-to-shoot signaling mediated by CLAVATA/ESR-related (CLE) peptides and their receptors. In the pea, mutations in genes Sym28 (CLV2-like) and Sym29 (CLV1-like), which encode receptors for CLE peptides, lead to the supernodulation phenotype, i.e., excessive nodule formation. The aim of the present study was to analyze the response of pea cv. ‘Frisson’ (wild type) and mutants P64 (sym28) and P88 (sym29) to complex inoculation with rhizobia, AM fungi and PGPB, with regard to biomass accumulation, yield and transcriptomic alterations. The plants were grown in quartz sand for 2 and 4 weeks after inoculation with either rhizobia (Rh) or complex inoculation with Rh + AM, Rh + PGPB, and Rh+AM+PGPB, and the biomass and yield were assessed. Transcriptome sequencing of whole shoots and roots was performed using a modified RNAseq protocol named MACE (Massive Analysis of cDNA Ends). In the experimental conditions, P88 (sym29) plants demonstrated the best biomass accumulation and yield, as compared to the wild type and P64 (sym28) plants, whereas P64 (sym28) had the lowest rate of biomass and seed yield. The transcriptome analysis showed that both supernodulating mutants more actively responded to biotic and abiotic factors than the wild-type plants and demonstrated increased expression of genes characteristic to late stages of nodule development. The roots of P64 (sym28) plants responded to AM+Rh treatment with upregulation of genes encoding plastid proteins, which can be connected with the activation of carotenoid biosynthesis (namely, the non-mevalonate pathway that takes place in root plastids). The more active response to symbionts in P88 (sym29) plants, as compared to cv. ‘Frisson’, was associated with counterregulation of transcripts involved in chloroplast functioning and development in leaves, which accompanies successful plant development in symbiotic conditions. Finally, the effect of retardation of plant aging upon mycorrhization on a transcriptomic level was recorded for cv. ‘Frisson’ but not for P64 (sym28) and P88 (sym29) mutants, which points towards its possible connection with the AON system. The results of this work link the plant’s autoregulation with the responsiveness to inoculation with beneficial soil microorganisms. RNAseq, transcriptomics, arbuscular mycorrhiza, nodule bacteria, complex inoculation, autoregulation of nodulation, garden pea

In pea (Pisum sativum L.), alleles of the Sym2 gene determine the specificity of the interaction with nodule bacteria (rhizobia). The Sym2^A allele present in landraces from Afghanistan provides higher selectiveness toward rhizobia than the Sym2^E allele present in European cultivars. Rhizobial strains possessing the nodX gene can interact with both Sym2^A and Sym2^E peas, while strains lacking nodX can interact only with Sym2^E peas. Here, we studied the previously obtained introgression line A33.18 bearing Sym2^A in a homozygous state in the genome of the European pea cultivar ‘Rondo’. A33.18 has proved its high selectiveness in pot experiments. Genome sequencing has shown that A33.18 possesses an 18.2 Mb region inherited from Afghanistan pea with 63 genes, including 5 receptor kinase genes, among which was the Sym2 candidate gene LykX. In a field experiment, under inoculation with the nodX⁺ strain TOM, over 95% of nodules of A33.18 contained TOM, as opposed to less than 8% of nodules containing TOM in the parental European cultivar ‘Rondo’. Thus, introgression of Sym2^A enabled peas to interact specifically with the nodX⁺ strain, favoring the formation of nodules by the strain from the inoculum and protecting peas from the indigenous soil microbiota.

Background. The active and careless applying of antibiotics in medicine and agriculture leads to the emergence of resistance to the existing antimicrobial drugs, which reduces the effectiveness of their use. One of the ways to solve this problem is the development of new antibiotics based on plant peptides with antimicrobial activity, for example plant defensins (which identified in all plants) and NCR peptides that are specifically synthesized in nodules of some leguminous plants. Materials and methods. In the present study, a meta-assembly of a transcriptome was constructed based on publicly available RNA-sequencing transcriptomes of pea nodules (Pisum sativum L.). This meta-assembly was used to search for sequences encoding antimicrobial peptides. Results. As a result, 55 and 908 unique sequences encoding defensins and NCR peptides, respectively, were identified. The recognition site for the signal peptidase was predicted and sequences were divided into the signal and mature part of the peptide. Among mature defensins, 22 peptides possess in silico predicted antimicrobial activity, and for the NCR peptides family their number was 422. Conclusion. Sequences encoding defensins and NCR peptides expressed in nitrogen-fixing pea nodules were identified. They are candidates for testing their antimicrobial activity in vitro.

Background. A major problem of the environmental pollution with heavy metals, including cadmium, requires an intensive study of the molecular and genetic mechanisms underlying the tolerance of plants to these toxic substances. In this study we present a comparative analysis of the expression of stress-related genes in two pea genotypes contrasting in tolerance to cadmium. Materials and methods. A unique mutant of pea SGECdt, characterized by the increased tolerance to cadmium, and initial line SGE were used. Gene expression was analyzed by Real Time PCR. Results. In the line SGE cadmium increase the expression of genes, encoding catalase, chitinase, chitinase-like protein PRP4A and dirigent protein PI206. In the mutant SGECdt cadmium increase the expression of genes, encoding chitinase, glutathione reductase and defensin DRR230. In control samples expression of genes encoding PRP4A and DRRR230 was enhanced in mutant SGECdt versus line SGE. Conclusion. It was shown that, the reaction of the mutant SGECdt at the molecular level differs from that of the line SGE. In the mutant SGECdt, a change in the expression of a number of genes is observed, which may indicate that cadmium entering the cell causes activation of defense reactions.