PtrIAA12-PtrARF8 Complex Regulates the Expression of PtrSAUR17 to Control the Growth of Roots in Poncirus trifoliata

The root system is an important determinant affecting the growth, adaptivity and stress resistance of citrus plants. Currently, the genetic regulatory network underlying root growth and development in citrus remains largely unknown. We report that a PtrAUX/IAA-ARF complex mediates the growth and development of roots in citrus through regulating the transcription of <i>PtrSAUR</i>. The auxin signaling pathway plays an essential role in regulating the growth and development of roots. In this study, we found that in citrus <i>Poncirus trifoliata</i>, <i>PtrIAA12</i>, encoding a canonical Aux/IAA protein, was highly expressed in the meristem and elongation zone of the root. Functional characterization showed that overexpression and silence of <i>PtrIAA12</i> significantly enhanced and suppressed the elongation of primary roots, respectively. Further analysis revealed that PtrIAA12 could interact with some members of <i>PtrARFs</i>, of which, PtrARF8 was identified to be the transcriptional factor of <i>PtrSAUR17</i>. Investigation of <i>PtrSAUR17</i> transgenic plants verified that <i>PtrSAUR17</i> is a key gene regulating the growth of roots in citrus. In conclusion, PtrIAA12 and PtrARF8 are the key members of the AUX/IAA-ARF complex in citrus controlling the growth and development of roots through regulating the transcription of <i>PtrSAUR17</i>.