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 PtrSAUR. The auxin signaling pathway plays an essential role in regulating the growth and development of roots. In this study, we found that in citrus Poncirus trifoliata, PtrIAA12, 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 PtrIAA12 significantly enhanced and suppressed the elongation of primary roots, respectively. Further analysis revealed that PtrIAA12 could interact with some members of PtrARFs, of which, PtrARF8 was identified to be the transcriptional factor of PtrSAUR17. Investigation of PtrSAUR17 transgenic plants verified that PtrSAUR17 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 PtrSAUR17.