Expression analysis suggests potential roles for PH-LIKE (PHL) genes in diploid strawberry Fragaria vesca L. seedling hormone response and fruit development

Acidity is a critical determinant for fruit sweetness in fleshy fruits. A recent molecular genetic study in sweet melon has revealed that the PH gene, encoding a protein most closely related to the Arabidopsis auxin efflux carrier family (PILS), acts as a critical regulator of fruit acidity. To provide insights into the possible role of PH-LIKE (PHL) genes in strawberry fruit acidity control, we identified a total of six PHL genes, FvPHL1 to FvPHL6, in a diploid strawberry fruit model system, Fragaria vesca L. Yellow Wonder 5AF7. These FvPHL genes exhibit distinct organ expression patterns. FvPHL1, the melon PH ortholog, was expressed in roots, leaves, flowers and fruits, while FvPHL2/3/6 were preferentially expressed in fruits. In addition, FvPHL genes exhibit fruit development and ripening-related expression patterns. Interestingly, FvPHL1/3/5/6 were all induced by exogenous auxin treatments in seedlings. In addition, FvPHL5 was slightly inhibited by abscisic acid (ABA), while the other five PHL genes were up-regulated by ABA in seedlings. However, auxin and ABA did not seem to affect FvPHL expression in developing fruits. These results indicate that some of FvPHL genes may be involved in auxin and ABA response in seedling growth and act in fruit development including acidity control.