Zearalenone (ZEN) and deoxynivalenol (DON) are mycotoxins produced by various species of Fusarium fungi. They contaminate agricultural products and negatively influence human and animal health, thus representing a serious problem of the agricultural industry. Earlier we showed that compactin, a secondary metabolite of Penicillium citrinum, is able to completely suppress the aflatoxin B1 biosynthesis by Aspergillus flavus. Using the F. culmorum strain FC-19 able to produce DON and ZEN, we demonstrated that compactin also significantly suppressed both DON (99.3%) and ZEN (100%) biosynthesis. The possible mechanisms of this suppression were elucidated by qPCR-based analysis of expression levels of 48 biosynthetic and regulatory genes. Expression of eight of 13 TRI genes, including TRI4, TRI5, and TRI101, was completely suppressed. A significant down-regulation was revealed for the TRI10, TRI9, and TRI14 genes. TRI15 was the only up-regulated gene from the TRI cluster. In the case of the ZEN cluster, almost complete suppression was observed for PKS4, PKS13, and ZEB1 genes, and the balance between two ZEB2 isoforms was altered. Among regulatory genes, an increased expression of GPA1 and GPA2 genes encoding α- and β-subunits of a G-protein was shown, whereas eight genes were down-regulated. The obtained results suggest that the main pathway for a compactin-related inhibition of the DON and ZEN biosynthesis affects the transcription of genes involved in the G-protein-cAMP-PKA signaling pathway. The revealed gene expression data may provide a better understanding of genetic mechanisms underlying mycotoxin production and its regulation.

PRODUCTION OF A CHIMERIC PROTEIN ELICITOR MF2/MF3 AND EVALUATION OF ITS PROTECTIVE ACTIVITY AGAINST TOBACCO MOSAIC VIRUS D.V. Erokhin, I.G. Sinelnikov, I.A. Shashkov, Y.А. Denisenko, S.B. Popletayeva, L.A. Shcherbakova, V.G. Dzhavakhiya

The ability of the MF3 protein from Pseudomonas fluorescens to protect plants by inducing their resistance to pathogenic fungi, bacteria, and viruses is well confirmed both in greenhouses and in the field; however, the molecular basis of this phenomenon remains unexplored. To find a relationship between the primary (and spatial) structure of the protein and its target activity, we analyzed the inducing activity of a set of mutants generated by alanine scanning and an alpha-helix deletion (ahD) in the part of the MF3 molecule previously identified by our group as a 29-amino-acid peptide working as the inducer on its own. Testing the mutants’ inducing activity using the “tobacco–tobacco mosaic virus” pathosystem revealed that some of them showed an almost threefold (V60A and V62A) or twofold (G51A, L58A, ahD) reduction in inducing activity compared to the wild-type MF3 type. Interestingly, these mutations demonstrated close proximity in the homology model, probably contributing to MF3 reception in a host plant.

The ability of a cold-shock protein CspD from Bacillus thuringiensis to protect both dicots and monocots against various pathogens is well confirmed under both greenhouse and field conditions; however, the molecular basis of this phenomenon at the transcriptomic level still remains unexplored. Expression profiles of some marker genes associated with SAR/ISR nonspecific resistance pathways and ROS scavengers were examined in CspD-treated Nicotiana tabacum plants, and the RNA-seq analysis of CspD-treated plants was first carried out. The ISR markers PDF1.2 and PR4 were overexpressed locally in treated tobacco leaves with the maximum 2.4- and 5.7-fold change, respectively, reached 12 h after the leaf treatment with CspD; PDF1.2 was also up-regulated 4.8-fold four days after the inoculation of treated plants with TMV. The ROS scavenger analysis demonstrated overexpression of Cu-Zn superoxide dismutase in both treated (with the maximum 5.4-fold change observed 6 h after the treatment) leaves and leaves from the upper tier (“system” leaves, 6.5-fold change observed 4 days after the treatment). The ROS assay confirmed endogenous accumulation of superoxide in CspD-treated leaves 6 and 24 h after the treatment. An in silico comparative study of Arabidopsis orthologs of highly up-regulated tobacco genes induced by CspD with Arabidopsis genes activated by some other molecular patterns revealed the specific CspD-induced expression of Cu-Zn superoxide dismutase and some other genes associated with light and cold responses. This study may contribute to a better understanding of cross-talking between abiotic stress and nonspecific immunity in plants.