However, unlike AtSPL7,
CRR1, and PpSBP2 are not members of SPL clade-I (Figure 1).
This suggests either that a function in copper homeostasis has
evolved multiple times independently, or has been lost multiple times following speciation and gene duplication (Figure 3).
Given the lack of data for this trait across a diversity of SPL genes,
future studies explicitly testing for copper homeostasis in divergent SPL protein clades will be required to distinguish between
these alternative hypotheses.