Dry mycelium of Penicillium chrysogenum activates defense via gene regulation of salicylic acid and jasmonic acid signaling in Arabidopsis

The dry mycelium of Penicillium chrysogenum (DMP) induces systemic acquired resistance (SAR), which enhances defenses in plants. To understand the molecular mechanisms involved in DMP-mediated signaling pathways, we examined the mRNA levels in Arabidopsis with jasmonic acid (JA), DMP or salicylic acid (SA) treatment compared with a control. RNA-Seq based transcriptome analysis revealed that the differentially expressed genes (DEGs) after DMP treatment were significantly enriched in three metabolism pathways shared by SA treatment and one additional pathway shared by JA treatment. Key DEGs, including PR1, EIN3 and FRK1, in the SA, JA/ethylene (ET) and pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI) pathways for inducing resistance were significantly regulated. Further quantitative real-time PCR (qRT-PCR) analysis revealed that DMP-mediated signaling cross-talked with JA and SA signaling and associated with PAMP-triggered immunity. SA accumulated significantly after DMP treatment. However some known small molecules inducing SA accumulation were not found in DMP. Together, we demonstrated that DMP treatment activated defense in SAR via gene regulation in the JA and SA pathways. These results provide molecular evidence for the mechanisms in the DMP induced SAR and could guide the further identification of the activators.