Title: Arabidopsis SRFR1 dampens defenses against herbivory by Spodoptera exigua and parasitism by Heterodera schachtii

Ellie Nguyen

Oklahoma State University, USA



Plants are constantly exposed to a variety of pathogenic microbes and pests. Thus, plants have developed diverse mechanisms to fine-tune defense responses to different types of enemies. Cross-regulation between these signaling pathways may allow the plant to prioritize one response over the other. Then, what is the connection between biotrophic microbe- and herbivorous insect–triggered resistance signaling pathways that converge on one gene? In previous work, we identified SUPPRESSOR OF rps4-RLD 1 (SRFR1), as a negative regulator of effector-triggered immunity against the bacterial pathogen Pseudomonas syringae pv. tomato. In the Arabidopsis accession RLD, the recessive srfr1 mutation confers ENHANCED DISEASE SUSCEPTIBILITY1 (EDS1)-dependent resistance to DC3000(avrRps4) in leaves. Here we examined whether SRFR1 also regulates resistance to a herbivorous insect in leaves and to a cyst nematode in roots. Surprisingly, srfr1-1 plants showed increased resistance to herbivory by the beet armyworm Spodoptera exigua and to parasitism by the cyst nematode Heterodera schachtii compared to RLD. Using quantitative real-time PCR (qRT-PCR) to measure the transcript levels of SA- and jasmonate/ethylene (JA/ET) pathway genes, we found that enhanced resistance of srfr1-1 plants to S. exigua correlated with specific upregulation of the MYC2-branch of the JA-pathway concurrent with suppression of the SA-pathway. In contrast, the greater susceptibility of RLD is accompanied by simultaneously increased transcript levels of SA-, JA-, and JA/ET-signaling pathway genes. This finding suggests a novel form of resistance in Arabidopsis to the biotrophic pathogen H. schachtii or a root-specific regulation of the SA pathway by EDS1, and places SRFR1 at an intersection between multiple defense pathways.