The CsTIE1–CsAGL16 module regulates lateral branch outgrowth and drought tolerance in cucumber

Drought stress and lateral branches are both important factors affecting crop yield. Cucumber is a widely planted vegetable crop that requires a large amount of water during its production and varieties with few lateral branches are preferred. However, the mechanisms regulating cucumber drought tolerance and lateral branch development remain largely unclear. The MADS-box transcription factor <i>AGAMOUS-LIKE 16</i> (<i>CsAGL16</i>) was recently found to be a key positive regulator in cucumber shoot branching acting by stimulating abscisic acid (ABA) catabolism. In this study, we demonstrated that cucumber TCP interactor containing EAR motif protein 1 (CsTIE1) directly interacts with CsAGL16 at protein level and promotes lateral branch outgrowth through the CsAGL16-<i>CsCYP707A4</i> mediated ABA pathway in cucumber. Additionally, mutation of <i>CsAGL16</i> resulted in decreased drought tolerance, while overexpression of <i>CsAGL16</i> significantly enhanced drought tolerance in cucumber. Similarly, the drought resistance of <i>Cstie1</i> mutants was significantly reduced. However, overexpression of <i>CsAGL16</i> can enhance the drought tolerance of <i>Cstie1</i> mutants and promote their lateral branch outgrowth. These results indicated that the CsTIE1-CsAGL16 module was crucial for both lateral branch development and drought response, providing a strategy for cultivating drought-tolerant cucumber varieties with appropriate branch outgrowth.