Arabidopsis MORC1 (Microrchidia) is required for multiple levels of immunity. We identified 14 MORC1-interacting proteins (MIPs) via yeast two-hybrid screening, eight of which have confirmed or putative nuclear-associated functions. While a few MIP mutants displayed altered bacterial resistance, MIP13 was unusual. The MIP13 mutant was susceptible to <i>Pseudomonas syringae</i>, but when combined with <i>morc1/2</i>, it regained wild-type resistance; notably, <i>morc1/2</i> is susceptible to the same pathogen. MIP13 encodes MED9, a mediator complex component that interfaces with RNA polymerase II and transcription factors. Expression analysis of defense genes <i>PR1</i>, <i>PR2</i>, and <i>PR5</i> in response to avirulent <i>P. syringae</i> revealed that <i>morc1/2 med9</i> expressed these genes in a slow but sustained manner, unlike its lower-order mutants. This expression pattern may explain the restored resistance and suggests that the interplay of MORC1/2 and MED9 might be important in curbing defense responses to maintain fitness. Indeed, repeated challenges with avirulent <i>P. syringae</i> triggered significant growth inhibition in <i>morc1/2 med9</i>, indicating that MED9 and MORC1 may play an important role in balancing defense and growth. Furthermore, the <i>in planta</i> interaction of MED9 and MORC1 occurred 24 h, not 6 h, postinfection, suggesting that the interaction functions late in the defense signaling. Our study reveals a complex interplay between MORC1 and MED9 in maintaining an optimal balance between defense and growth in Arabidopsis.