CsIAGLU Regulates the Angle of Leaf Petiole by Affecting Endogenous Content of Auxin in Cucumber (Cucumis sativus L.)

The leaf angle is an important factor determining plant shoot architecture that may boost crop yield by increasing photosynthetic efficiency and facilitating high-density planting. Auxin is an important phytohormone involved in leaf angle regulation. Here, we identified two Single-Nucleotide Polymorphisms (SNPs) in the Indoleacetic Acid (IAA) glucosyltransferase gene CsIAGLU in 80 re-sequenced cucumber lines, of which the CsIAGLU(717G,1234T) is the dominant allele associated with a small leaf pedicle angle (LPA), whereas CsIAGLU(717C,1234A) is linked with a large LPA. CsIAGLU was highly expressed in leaves and petioles. In natural cucumber populations, the expression of CsIAGLU was negatively correlated with the LPA. The mutation of CsIAGLU induced by the CRISPR-Cas9 system resulted in elevated free IAA levels and enlarged cell expansion on the adaxial side of the petiole base, thus producing a greater LPA. Consistently, exogenous IAA treatment led to increased LPA and cell size. Therefore, our findings suggest that CsIAGLU functions as a negative regulator of LPA development via auxin-mediated cell expansion in cucumber, providing a valuable strategy for cucumber breeding with small LPAs.