Figure 6.
Adventitious Root Initiation: A Proposed Model for a Regulatory Pathway.
ARF6, ARF8, and ARF17 and their regulatory microRNAs interact in a complex network (Gutierrez et al., 2009) and act upstream of GH3.3, GH3.5, and GH3.6. ARF6 and ARF8 are positive regulators of the three GH3s, whereas ARF17 is a negative regulator. GH3.3, GH3.5, and GH3.6 control each other’s expression through a pathway yet to be identified. The three GH3 genes control JA homeostasis. The JA-Ile level in the hypocotyl is determined by the JA level. The level of JA-Ile negatively regulates adventitious rooting through the activation of the COI1 signaling pathway. In conclusion, auxin controls adventitious root initiation through the activation of ARF6 and ARF8 proteins, leading to a downregulation of the inhibiting COI1 signaling pathway.