LC–MS Analysis for Paenibacillus yonginensis DCY84 T and Silicon Informs the Significance of Suppressed Unsaturated Fatty Acids

We reported in our recent studies that the combined treatment of Paenibacillus yonginensis DCY84 T (DCY84 T ) and Silicon (Si) promotes initial plant growth and increases resistance to biotic and abiotic stress. To understand the molecular background of these phenotypes, Liquid Chromatography Mass Spectrometry (LC–MS) analysis was performed, and it was confirmed that unsaturated fatty acid metabolites such as oleic acid and linoleic acid decreased in response to the combined treatment of DCY84 T and Si. The stearoyl-acyl carrier protein desaturase (SACPD) introduces the cis double bond into the acyl-ACPs at C9, resulting in the production of unsaturated fatty acid. We identified OsSSI2 encoding SACPD in rice and found that the expression of OsSSI2 was reduced under DCY84 T and Si treatment. Furthermore, qRT-PCR analysis revealed that the expression of OsWRKY45 , which is downstream of OsSSI2 , was upregulated in response to DCY84 T and Si treatment. These results enable the speculation that activation of the salicylic acid (SA)-responsive gene, OsWRKY45, may contribute to enhancing biological stress resistance. Based on this, we propose a probable model for the rice defense pathway following DCY84 T and Si treatment. This model retains a WRKY45-dependent but NH1(NPR1)-independent SA signaling pathway.