Arabidopsis SRFR1 Dampens Defenses Against Herbivory by Spodoptera exigua and Parasitism by Heterodera schachtii

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 army worm 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 places SRFR1 at an intersection between multiple defense pathways.