The polymerase-associated factor 1 complex modulates the growth-defense tradeoff in <i>Arabidopsis</i>

Plants have evolved sophisticated mechanisms to balance growth and defense. The evolutionarily conserved polymerase-associated factor 1 complex (PAF1C) plays multiple roles in transcription. Here, we show that PAF1C regulates the growth-defense tradeoff by repressing defense genes expression in <i>Arabidopsis</i>. Loss of PAF1C leads to increased expression of defense genes, enhanced disease resistance, but compromised growth. Mechanistically, PAF1C binds to defense genes, where it interacts with histone deacetylases, such as HDA6, to promote histone deacetylation, thereby repressing defense genes expression. The plant immune hormone salicylic acid (SA) promotes the interaction between PAF1 and the SA receptor NPR1, which functions as an E3 ubiquitin ligase to mediate the polyubiquitination and degradation of PAF1. Genetically, loss of PAF1 suppresses the immune defects of the <i>npr1</i> mutant, supporting the notion that PAF1 functions downstream of NPR1. Collectively, this study identifies the NPR1-PAF1C-HDA6 module that regulates the growth-defense tradeoff.