Effect of Endophytic Bacteria Bacillus velezensis M66 on Transcriptional Activity of the Genes of the RNA Interference System upon Development of Defense Responses Against the Late Blight Pathogen Phytophthora infestans (Mont.) de Bary

The effect of bacteria Bacillus velezensis strain М66 on resistance of potato plants to oomycete Phytophthora infestans (Mont.) de Bary that causes late blight disease was investigated. For the first time, a rise in the number of endophytic bacteria B. velezensis М66 in internal tissues of plants after infection with the pathogen as compared with plants solely inoculated with bacteria was shown. A considerable reduction in the area showing the symptoms of late blight disease was shown irrespective of virulence of the used strain of pathogen. Formation of plant resistance under the effect of B. velezensis М66 cells was accompanied by activation of trypsin inhibitor and peroxidases; accumulation of hydrogen peroxide and transcripts of genes encoding inhibitors of proteinases, β-1,3-glucanase, and anionic peroxidase; and reduction in the level of transcripts of gene PR1: a marker of the development of salicylate-depending reactions. As to the system of RNA interference, it was shown that aggressive strain P. infestans Sn stimulated accumulation of transcripts of the gene encoding Dicer-like protein (DCL) in potato plants, whereas less aggressive strain P. infestans 1840 activated genes DCL and Ago4. Plant treatment with bacteria B. velezensis М66 promoted accumulation of gene Ago1 transcripts both in healthy and infected plants. Inoculation of plants with bacteria and subsequent infection with oomycete promoted accumulation of transcripts of all the examined genes involved in the system of RNA interference. Thus, inoculation of plants with cells of endophytic bacteria B. velezensis strain M66 promotes formation of resistance to oomycete P. infestans by means of efficient priming of plant immune potential.