Expression of five expansin genes during softening of Fragaria chiloensis fruit: Effect of auxin treatment

The Chilean strawberry fruit (Fragaria chiloensis) has potential as a new exotic berry. The rate of softening differs between F chiloensis and its related species Fragaria x ananassa. The expression profiles of five expansin genes isolated from E x ananassa were analyzed during softening of F chiloensis fruit and the regulatory effect of auxins on them observed. The rapid decrease in fruit firmness observed between the large green and the turning stages of E chiloensis correlated with the large increase in transcript accumulation of FaEXP2 and FaEXP5. FaEXP4 and FaEXP6 had lower expression levels in F chiloensis than in F x ananassa, and expression profiles were not related to fruit softening. Auxins strongly repressed the expression of FaEXP1 and FaEXP2, and had a minor repressive effect on FaEXP4 and FaEXP5. In addition, tissue-specific expression was probed in different E chiloensis tissues: FaEXP2 and FaEXP5 transcripts were found only in fruit tissues, while FaEXP4 and FaEXP6 transcripts were also found in runners, roots, leaves and flowers. In conclusion, most of the strawberry-expansin genes are expressed in E chiloensis and some family members are closely related to fruit softening, especially FaEXP2 and FaEXP5. This study reveals the repressive effect of auxins on the expression of those expansin genes related to softening in E chiloensis fruit. (C) 2009 Elsevier B.V. All rights reserved.