| Summary: | The PIN-FORMED (PIN) proteins represent the most important polar auxin transporters in plants. Here, we characterized the <i>PIN</i> gene family in two olive genotypes, the <i>Olea europaea</i> subsp. <i>europaea</i> var. <i>sylvestris</i> and the var. <i>europaea</i> (cv. ‘Farga’). Twelve and 17 <i>PIN</i> genes were identified for vars. <i>sylvestris</i> and <i>europaea</i>, respectively, being distributed across 6 subfamilies. Genes encoding canonical OePINs consist of six exons, while genes encoding non-canonical OePINs are composed of five exons, with implications at protein specificities and functionality. A copia-LTR retrotransposon located in intron 4 of <i>OePIN2b</i> of var. <i>europaea</i> and the exaptation of partial sequences of that element as exons of the <i>OePIN2b</i> of var. <i>sylvestris</i> reveals such kind of event as a driving force in the olive <i>PIN</i> evolution. RNA-seq data showed that members from the subfamilies 1, 2, and 3 responded to abiotic and biotic stress factors. Co-expression of <i>OePINs</i> with genes involved in stress signaling and oxidative stress homeostasis were identified. This study highlights the importance of <i>PIN</i> genes on stress responses, contributing for a holistic understanding of the role of auxins in plants.
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