Fig. 8

A working model for MdFLP in response to gravity during the gravitropism of adventitious roots of apple. Under gravity, MdFLP acts upstream of PIN-FORMED (MdPIN3 and MdPIN10) and directly regulates their expression by binding to the AGCCG motif of their promoters. Additionally, the apple auxin response factor MdARF19 influences the expression of those auxin efflux carriers and the establishment of the GSA of adventitious roots of apple in response to gravity by direct activation of its expression of MdFLP. On the other hand, MdARF19 may also directly regulate the expression of other PINs by affecting auxin reflux and thus regulating GSA