An immune-inducible trihelix transcription factor suppresses bacterial resistance in Arabidopsis thaliana

The plant innate immunity consists of the two interconnected mechanisms, pattern-triggered immunity (PTI) and effector-triggered immunity (ETI). Although much is known about how plants trigger immune responses upon pathogen recognition, the genetic program by which plants avoid an overshoot in pathogen-triggered immune responses remains largely unknown. Here, we discovered a trihelix transcription factor, GT-3a, as an immune-inducible negative regulator of bacterial resistance in Arabidopsis thaliana. Analysis of public RNA-seq data revealed that GT-3a is specifically induced by ETI activation not by PTI activation. Overexpression of GT-3a suppressed resistance against the bacterial pathogen Pseudomonas syringae pv. tomato DC3000 (Pto) and Pto-elicited expression of salicylic acid (SA)-responsive genes. Our results suggest that transcriptional induction of GT-3a circumvents the overshooting of SA-mediated defense responses during ETI. We transformed Arabidopsis thaliana Col-0 (CS60000) to generate transgenic lines that express C-terminally GFP-fused GT-3a transcription factor under the control of cauliflower mosaic virus 35S promoter. Col-0 and a selected transgenic line (GT3a-OE) were grown on soil in a growth chamber at 22 °C and 60% relative humidity with a 10/14 hours light/dark cycle. Leaves of 4- to 5-week-old Col-0 and GT3a-OE line were infiltrated with Pseudomonas syringae pv. tomato DC3000 (Pto) at OD600 0.001 using a needleless syringe. The infiltrated leaves were harvested 24 hours after infiltration. To generate three biological replicates, three independent experimental trials were carried out.