Induction of Systemic Resistance against Aphids by Endophytic Bacillus velezensis YC7010 via Expressing PHYTOALEXIN DEFICIENT4 in Arabidopsis

Abstract

Aphids are the most destructive insect pests. They suck the sap and transmit plant viruses, causing widespread yield loss of many crops. A multifunctional endophytic bacterial strain Bacillus velezensis YC7010 has been found to induce systemic resistance against bacterial and fungal pathogens of rice. However, its activity against insects attack and underlying cellular and molecular defense mechanisms are not elucidated yet. Here, we show that root drenching of Arabidopsis seedlings with B. velezensis YC7010 can induce systemic resistance against green peach aphid (GPA), Myzus persicae. Treatment of bacterial suspension of B. velezensis YC7010 at 2 × 107 CFU/ml to Arabidopsis rhizosphere induced higher accumulation of hydrogen peroxide, cell death, and callose deposition in leaves compared to untreated plants at 6 days after infestation of GPA. Salicylic acid, jasmonic acid, ethylene, and abscisic acid were not required to confer defense against GPA in Arabidopsis plants treated by B. velezensis YC7010. Bacterial treatment with B. velezensis YC7010 significantly reduced settling, feeding and reproduction of GPA on Arabidopsis leaves via strongly expressing senescence-promoting gene PHYTOALEXIN DEFICIENT4 (PAD4) while suppressing BOTRYTIS-INDUCED KINASE1 (BIK1). These results indicate that B. velezensis YC7010-induced systemic resistance to the GPA is a hypersensitive response mainly dependent on higher expression of PAD4 with suppression of BIK1, resulting in more accumulation of hydrogen peroxide, cell death, and callose deposition in Arabidopsis.

Arabidopsis ACTIN-DEPOLYMERIZING FACTOR3 Is Required for Controlling Aphid Feeding from the Phloem

“…However, since the GPA infestation-associated increase in callose deposition was also attenuated in the pad4 mutant, we suggest that the impact of ADF3 on callose deposition in response to GPA infestation is likely exerted via ADF3's engagement of the PAD4 defense-signaling pathway. The contribution of PAD4 in promoting callose deposition is further supported by a recent study, which showed that the endophytic Bacillus velezensis-induced resistance against the GPA was accompanied by an increase in callose deposition, which was dependent on PAD4 (Rashid et al, 2017).…”

Induction of Systemic Resistance against Insect Herbivores in Plants by Beneficial Soil Microbes

“…Rhizobacterial stimulation of LOX activates the oxylipin pathway to change fatty acids into reactive hydroperoxides, which can be further modified into diverse defense metabolites ( Shah, 2005 ; Cawoy et al, 2014 ). Exposure of Arabidopsis roots with the endophytic bacterium, B. velezensis YC7010, can induce systemic resistance to aphids due to the increased accumulation of H 2 O 2 , cell death and deposition of callose in leaves ( Rashid et al, 2017 ). The collective data indicate that ROS accumulation in plants interacting with microbes is an early defense response against insect predation.…”

Silicon modulates multi-layered defense against powdery mildew in Arabidopsis

“…3) or overexpression of PMR4/GSL5 (Ellinger et al 2013) confers resistance to powdery mildew. Lastly, PAD4-dependent resistance to aphids is also associated with increased callose deposition (Rashid et al 2017), similar to Simediated resistance to insects (Yang et al 2018) or even nematodes (Zhan et al 2018), despite that in the latter cases whether resistance is PAD4-dependent remains to be tested. Therefore, it is possible that PAD4 (but not EDS1) may play a critical role in the deposition of a basal level of PMR4-dependent callose to papillae, thus explaining the PAD4-dependence of high Si-mediated resistance against powdery mildew pathogens.…”