A Loss of DPA4 Mutant Reveals That the Boundary Gene CUC2 Promotes Adventitious Root Formation in Arabidopsis Leaf Explants via Repression of ULT1 and Increased Auxin Biosynthesis

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 sig-nal rapidly induces in leaf explants the expression of genes encoding enzymes of auxin biosynthesis resulting in elevated auxin levels and facilitated 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 repressor of CUP-SHAPED COTYLEDON 2 (CUC2), inhibits AR formation in de-tached leaves. Leaf explants of dpa4-2 and cuc2-1D mutants displayed both elevated CUC2 mRNA levels and increased rooting rates. We observed reduced expression of ULTRAPETALA1 (ULT1), a negative regulator of DNRR, while the auxin biosynthesis genes ASA1, YUC4, and YUC9 were upregulated in both mutants. Through pharmaco-logical 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 dpa4-2 cuc2-1D double mutants indicates that similar mechanisms promotes DNRR in both mutants. In summary, our study suggests that DPA4 suppresses AR formation likely by repression of CUC2 and activation of ULT1, which, in turn, suppresses endogenous auxin biogenesis and DNRR.