Induction of New Defensin Genes in Tomato Plants via Pathogens-Biocontrol Agent Interaction

Abstract

Defensins and defensin-like peptides are functionally diverse and commonly presented as an immune reaction between plant and pathogen. Trichoderma viride and Bacillus subtilis as biological control agents, were inoculated into the soil, to suppress the activity of the pathogenic fungi Fusarium oxysporum and Rhizoctonia solani on tomato. The up- and down-regulated genes were examined in both treated and non-treated plants, using differential display technique. In treated plants, many up-regulated genes (21) with different molecular sizes, ranging from 50 to 7000 bp, were observed. Only four up-regulated genes were isolated from plants treated with B. subtilis+R. solani. The sequence analysis revealed that the identified genes were defensin genes; Amino Acid/Auxin Permease Family, Endopolygalacturonase PG1, Fructose-1,6-bisphosphatase and glycosyl transferase. Moreover, chitinase gene, defensin genes (DF1 and DF2) were quantitatively determined using RT-PCR. The comparative expression level of the three induced genes was exponentially increased as a function of time, after the application of the biological control agents. However, while the expression levels of DF1 and DF2 were high in plants infected with either F. oxysporum or R. solani in the beginning of the experiment, the highest expression level of these genes was attained in the tomato plant treated with either T. viride or B. subtilis, after 24 hour post inoculation.