DPA4 Suppresses Adventitious Root Formation via Transcriptional Regulation of CUC2 and ULT1, Decreasing Auxin Biosynthesis in Arabidopsis Leaf Explants

Plants have the capacity to form adventitious roots (ARs) from detached aerial organs, a process known as de novo root regeneration (DNRR). In Arabidopsis, wounding signals rapidly induce in leaf explants the expression of genes encoding enzymes of auxin biosynthesis, resulting in elevated auxin levels and facilitating AR formation. Here, we report that DEVELOPMENT-RELATED POLYCOMB TARGET IN THE APEX 4 (DPA4/NGAL3), a well-known regulator in seed size and leaf margin development, and a repressor of <i>CUP-SHAPED COTYLEDON 2</i> (<i>CUC2</i>), inhibits AR formation in detached leaves. Leaf explants of <i>dpa4-2</i> and <i>cuc2-1D</i> mutants displayed both elevated <i>CUC2</i> mRNA levels and increased rooting rates. We observed reduced expression of <i>ULTRAPETALA1</i> (<i>ULT1</i>), a negative regulator of DNRR, while the auxin biosynthesis genes <i>ASA1</i>, <i>YUC4</i>, and <i>YUC9</i> were upregulated in both mutants. Through pharmacological inhibition of YUCCA-mediated auxin biogenesis, we obtained evidence that the enhanced AR formation in both mutants is at least partially a result of increased auxin production. Genetic analysis of <i>dpa4-2 cuc2-1D</i> double mutants indicates that similar mechanisms promote DNRR in both mutants. In summary, our study suggests that <i>DPA4</i> suppresses AR formation likely by repression of <i>CUC2</i> and activation of <i>ULT1</i>, which, in turn, suppresses endogenous auxin biogenesis and DNRR.