The <scp>SCOOP12</scp> ‐ <scp>MIK2</scp> module regulates Arabidopsis root meristem development via the <scp>PLETHORA</scp> transcription factors

Plants have evolved intricate mechanisms to balance growth and defense through complex signaling networks. Previous studies have focused on aerial parts or crop yield, but little is known about the regulation of root growth under pathogen attack. Here, we report that the SERINE RICH ENDOGENOUS PEPTIDE12 (SCOOP12) immune signaling peptide regulates root meristem development via the receptor-like kinase MALE DISCOVERER 1-INTERACTING RECEPTOR-LIKE KINASE 2 (MIK2) and the MAPK cascade in Arabidopsis. We demonstrated that SCOOP12 treatment reduced the number of root meristematic cells by suppressing the expression of key molecular regulators, including PLETHORA1 (PLT1) and PLT2, which are essential for maintaining root stem cell niche (SCN) activity. Physiological and cell biological experiments revealed that MIK2 and MPK6 are required for SCOOP12-mediated root growth regulation, as the mik2 and mpk6 mutants presented reduced sensitivity to SCOOP12-induced effects. Further biochemical evidence indicates that MPK6 directly phosphorylates PLT1 and PLT2. The plt1-4 plt2-2 double mutant also presented diminished responses to SCOOP12, confirming the central role of PLT1/2 in this regulatory network. Our work elucidated a molecular pathway through which SCOOP12 modulates root meristem activity, providing insights into the trade-off between plant growth and immunity.