CsSHR1 regulates compact plant architecture by mediating cell division in cucumber

A compact plant architecture is a crucial agronomic trait that enhances crop yields by allowing for increased planting densities, thereby meeting the growing food requirements. We previously identified a GRAS family transcription factor, SCARECROW-LIKE28 (CsSCL28), from cucumber (Cucumis sativus L.) that regulates this process. However, the underlying regulatory mechanism remains unknown. Here we demonstrated that CsSCL28 physically interacts with another GRAS family transcription factor SHORT-ROOT1 (CsSHR1). Knockout of CsSHR1 resulted in reduced plant height and leaf size. Overexpression of CsSHR1 regulates plant height and leaf size in cucumber in a dose-dependent manner. CsSHR1 positively regulates the transcription of CsSCL28. Genetic analyses revealed that CsSHR1 is epistatic to CsSCL28 in regulating cucumber plant architecture. Furthermore, CsSHR1 can directly activate the transcription of CsCYCD3;3, and ectopic overexpression of CYCD3;3 leads to an enlargement in leaf area. Biochemical data showed that CsSCL28 physically interacted with CsSHR1 to synergize its function by promoting the CsSHR1-mediated CsCYCD3;3 transcriptional activation. Importantly, appropriate overexpression of CsSHR1, which exhibits compact plant architecture, does not affect the yield per plant in cucumber. Thus, our findings reveal the genetic and molecular mechanism by which the CsSHR1 mediates compact plant architecture in cucumber. Our findings provide new gene targets for cucumber dense planting.