Plants are able to discriminate and respond to structurally related chitooligosaccharide (CO) signals from pathogenic and symbiotic fungi. In model plants Arabidopsis thaliana and Oryza sativa LysM-receptor like kinases (LysM-RLK) AtCERK1 and OsCERK1 (chitin elicitor receptor kinase 1) were shown to be involved in response to CO signals. Based on phylogenetic analysis, the pea Pisum sativum L. LysM-RLK PsLYK9 was chosen as a possible candidate given its role on the CERK1-like receptor. The knockdown regulation of the PsLyk9 gene by RNA interference led to increased susceptibility to fungal pathogen Fusarium culmorum. Transcript levels of PsPAL2, PsPR10 defense-response genes were significantly reduced in PsLyk9 RNAi roots. PsLYK9’s involvement in recognizing short-chain COs as most numerous signals of arbuscular mycorrhizal (AM) fungi, was also evaluated. In transgenic roots with PsLyk9 knockdown treated with short-chain CO5, downregulation of AM symbiosis marker genes (PsDELLA3, PsNSP2, PsDWARF27) was observed. These results clearly indicate that PsLYK9 appears to be involved in the perception of COs and subsequent signal transduction in pea roots. It allows us to conclude that PsLYK9 is the most likely CERK1-like receptor in pea to be involved in the control of plant immunity and AM symbiosis formation.

The aim of this study was to find out why after joint inoculation of the substrate with the phytopathogenic fungus Fusarium culmorum and the antagonistic bacterium Pseudomonas fluorescens the amount of the fungus on the root surface in the beginning of the colonization was greater on the roots colonized by the bacterium than on control roots. This phenomenon is especially interesting because joint inoculation with P. fluorescens was always followed by a considerable decrease in the incidence of Fusarium root rot. In two experiments barley was grown in sterile vermiculite inoculated only with F. culmorum, only with P. fluorescens and jointly with the fungus and the bacterium. In the control, vermiculite was not inoculated with any microorganisms. After the removal from the vermiculite, barley plants were transferred into deionized water for the collection of root exudates. The duration of barley growth in the vermiculite and in the water was different in the two experiments. The exudates were tested for their ability to elicit chemotropism in F. culmorum and influence its growth. We did not observe any chemotropism of F. culmorum towards barley root exudates. However, the exudates of the barley colonized by the bacterium stimulated the growth of fungal germ tubes. Using an ultra-performance liquid chromatography system, we found that experimental conditions influenced the quantitative composition of the exudates. The amount of amino acids in the solution of exudates decreased considerably after a prolonged growth of control barley in water, while the presence of P. fluorescens resulted in a considerably increase of the amount of amino acids in the exudates. The exudates of barley colonized by P. fluorescens contained much more glucose, lactic acid and several amino acids than the exudates of control barley. These components are known to be necessary for the growth of F. culmorum. Their presence in the exudates of barley colonized by P. fluorescens seems to be the reason of a more active colonization by the fungus of barley roots colonized by the bacterium.

Plant residues are the main source of humus and some nutrients in soils. The composting of organic waste using modifiers is a promising way to obtain high-quality organic fertilizers. Here, the effect of biochar and calcium carbonate on the abundance and taxonomic composition of bacteria and fungi in mature plant compost has been studied using metagenomic analysis. Plant materials with different initial C:N ratios—low (22, clover), medium (38, rye) and high (68, oats)—served as composting materials in the pot experiment. The plant material mixed with sterile sand was modified by the addition of biochar or calcium carbonate. Both ameliorants increased pH values and humic acid content in composts irrespective of plant material composition. Representatives of the phyla Proteobacteria, Actinobacteriota and Firmicutes dominated among bacteria and representatives of the division Ascomycota dominated among fungi in the mature composts, as in the initial plant samples. The abundances of bacteria and fungi in the cereal composts were higher than in the composts with clover. The effect of biochar and calcium carbonate on the number and taxonomic composition of bacteria and fungi in composts from the same plant material was similar, while the effect of reagents in composts from different raw materials was ambiguous. No one dominant group of bacteria was found to develop in response to biochar or calcium carbonate application in any of the types of composts studied. However, the structure of the fungal community both at the phylum and genus levels changed significantly under the influence of these additives. The addition of calcium carbonate and biochar led to an increase in the abundance of the same groups of fungi, but this increase was different for composts made from different plant materials.

INFLUENCE OF BIOCHAR ON THE TAXONOMIC COMPOSITION AND STRUCTURE OF PROKARYOTIC COMMUNITIES IN AGRO SODDY-PODZOLIC SOIL V.Yu. Shahnazarova, N.E. Orlova, Е.Е. Оrlova, Т.А. Bankina, К.L. Yakkonen, Е.Ya. Rizhiya, A.A. Kichko

ИЗМЕНЕНИЯ ТАКСОНОМИЧЕСКОГО СОСТАВА И СТРУКТУРЫ ПРОКАРИОТНОГО СООБЩЕСТВА АГРОДЕРНОВО-ПОДЗОЛИСТОЙ ПОЧВЫ ПРИ ВНЕСЕНИИ БИОУГЛЯ В.Ю. ШАХНАЗАРОВА, Н.Е. ОРЛОВА, Е.Е. ОРЛОВА, Т.А. БАНКИНА, К.Л. ЯККОНЕН, Е.Я. РИЖИЯ, А.А. КИЧКО

One of the important traits of plant growth promoting rhizobacteria (PGPR) is biocontrol of phytopathogens. Some PGPR metabolize phytohormone abscisic acid (ABA), however the role of this trait in plant-microbe interactions is scarcely understood. Phytopathogenic fungi produce ABA and use this property as a negative regulator of plant resistance. Therefore, interactions between ABA-producing necrotrophic phytopathogen Botrytis sp. BA3 with ABA-metabolizing rhizobacterium Rhodococcus sp. P1Y was studied in batch culture and in gnotobiotic hydroponics with sunflower seedlings. Rhizobacterium P1Y possessed no antifungal activity against BA3 and metabolized ABA, which was synthesized by BA3 in vitro and in associations with sunflower plants infected with this fungus. Inoculation with BA3 and application of exogenous ABA increased root ABA concentration and inhibited root and shoot growth, suggesting involvement of this phytohormone in pathogenesis process. Strain P1Y eliminated negative effects of BA3 and exogenous ABA on root ABA concentration and plant growth. Both microorganisms significantly modulated hormonal status of plants affecting indole-3-acetic, salicylic, jasmonic and gibberellic acids, as well as cytokinins concentrations in sunflower roots and/or shoots. The hormonal effects were complex and could be due to production of phytohormones by microorganisms, changes in ABA concentrations and multiple levels of crosstalk in hormone networks regulating plant defense. The results suggest the counteraction of rhizobacteria to ABA-producing phytopathogenic fungi through the metabolism of fungal ABA. This expands our understanding of the mechanisms related to biocontrol of phytopathogens by PGPR.