The CsANT1-CsCUC2/CsCYCD3;1 regulatory module coordinates leaf margin development and cell proliferation in cucumber.

Leaf shape is a critical agronomic trait that determines plant architecture and cultivation value, but its genetic and molecular mechanisms remain elusive. Here, we found two natural cucumber mutants, jtll and 10yjy, characterized by little, deeply lobed leaves with reduced cell number and auxin levels. Despite originating from distinct genetic backgrounds, both mutants were fine-mapped to the same locus encoding the AP2-like transcription factor AINTEGUMENTA 1 (CsANT1), thereby revealing a novel role of ANT in leaf lobe formation. Furthermore, CsANT1 modulates auxin distribution along leaf margins via repressing the transcription of CsCUC2, which governs leaf margin morphogenesis. Meanwhile, CsANT1 directly activates Cyclin D3 (CsCYCD3;1) transcription to promote cell proliferation and regulate leaf size. Thus, CsANT1 coordinates leaf morphogenesis by synergistically regulating auxin transport and cell proliferation. Notably, the little and lobed leaf architecture conferred by CsANT1 resembles maple leaves and has high ornamental value. Cucumber varieties derived from this natural mutant have already been commercialized and highly popular for home potted horticulture. Overall, our findings reveal a CsANT1-CsCUC2/CsCYCD3;1 regulatory module governing leaf morphogenesis and provide genetic resources and a theoretical foundation for cucumber leaf shape improvement.