A Novel <scp>AP2</scp> / <scp>ERF</scp> Transcription Factor Controls Trichome Initiation and Fruit Development in Cucumber

Trichomes, the hair-like outgrowths of the plant epidermis, are critical for defence, reproduction and development. However, the underlying molecular mechanisms governing their initiation remain elusive. Here, we identified CsGL2, an AP2/ERF transcription factor, as a key integrator controlling trichome initiation and fruit development in cucumber. Genetic and molecular studies indicate that CsGL2 activates CsGL1/Mict, subsequently triggering the morphogenesis of multicellular trichomes. Beyond epidermal fate, CsGL2 upregulates the tubercle regulator Tu together with the cytokinin rate-limiting enzyme gene IPT1, thereby initiating fruit tubercles through cytokinin-linked pathways. Notably, we found that ovule-specific CsGL2 activates the parthenocarpy gene CsNPF1, and CsGL2 overexpression markedly increases the frequency of seedless fruit set. Thus, our findings establish a switch-based mechanism for progressive cell-fate specification in multicellular epidermal organs. This reveals how a single transcription factor integrates transcriptional and hormonal pathways to coordinate distinct developmental programmes.