*4.4. Ka/Ks Analysis of TPS Family Members in Rosaceae*

We chose six representative Rosaceae species for selection pressure analysis, including *P. persica*, *P. mume*, *M. domestica*, *P. betulifolia*, *F. vesca*, and *R. chinensis*. For each species, its TPSs paralogs were determined based on their phylogenetic relationship. If they belong to the same clade and derive from a single gene that was duplicated recently, we assumed they were paralogs. Sometimes those paralogs that arose from a duplication after the speciation event are called "within-species" paralogs [22]. The CDS and protein sequences of each TPS pair were used to compute the Ka (non-synonymous rates) and Ks (synonymous rates) by Ka/Ks calculator (http://services.cbu.uib.no/tools/kaks, accessed on 2 Octomber 2021). The date (*T*) of the duplication events was estimated by the formula *T* = Ks/2λ, where λ represents the estimated clock-like rate of synonymous substitution; in dicots, it was 1.5 × <sup>10</sup>−<sup>8</sup> substitutions/synonymous site/year [35].
