Role of WRKY20 transcription factor and raffinose in plant defense responses upon Bacillus amyloliquefaciens strain 5113-mediated priming in Arabidopsis thaliana

Abstract: Biocontrol through beneficial bacteria-mediated priming can promote plant growth and increase resistance to biotic and abiotic stress. Bacillus amyloliquefaciens strain 5113 has been identified as a promising candidate for priming by increasing stress resistance and promoting growth in oil seed rape (Brassica napus). Recent findings suggest that WRKY20 transcription factor and the oligosaccharide raffinose are involved in increased resistance upon B. amyloliquefaciens strain 5113-mediated priming. The present study aimed to further elucidate the role of WRKY20 transcription factor in plant defense as well as the involvement of WRKY20 and raffinose in plant defense upon B. amyloliquefaciens strain 5113-mediated priming. Also, the effect on plant starch metabolism upon priming was studied by GUS analysis of isoamylase (AtISA1, AtISA2 and AtISA3) expression in promoter+target::GFP/GUS transgenic plants. Role of WRKY20 transcription factor in plant defense was studied through gene expression analysis upon treatment with salicylic acid (SA) and methyl jasmonate (MeJA). In order to elucidate the role of WRKY20 and raffinose response to Pseudomonas syringae DC3000 infection in primed and non-primed Arabidopsis wrky20, rs2 and rs6 mutants and wild-type Col-0 was studied. WRKY20 was shown to be up-regulated by SA treatment and down-regulated upon MeJA treatment. The infection study revealed an increased resistance in primed wild-type Arabidopsis plants compared to non-primed while no priming effect could be seen for wrky20, rs2 and rs6 mutants. Based on these and previous findings, WRKY20 appears to function as regulator in the JA and SA dependent signaling pathways. Also, raffinose appears to be essential to increase plant resistance through B. amyloliquefaciens strain 5113-mediated priming. GUS analysis of AtISA1::GFP/GUS, AtISA2::GFP/GUS and AtISA3::GFP/GUS showed a distinct up-regulation of AtISA1 in primed plants indicating an increased starch production. Taken together, this study suggests B. amyloliquefaciens strain 5113 as a promising candidate for biological control.