The Making of Fruit: Genomic Approaches to Understand Fruit Set in Wild Strawberry

Fruits represent a key evolutionary innovation for seed disposal and are only formed upon successful fertilization of flowers. The molecular mechanism underlying this fertilization-dependent fruit initiation, termed fruit set, is investigated in wild strawberry Fragaria vesca. The wild strawberry is emerging as a model system for the cultivated strawberry due to wild strawberry's diploidy, small and sequenced genome, and available genetic and genomic resources. RNA-seq was performed to investigate the molecular events before and after fertilization in dissected fruit tissues. Bioinformatic analysis of the RNA-seq data focuses on identifying the earliest signals responsible for fruit set. Analysis of phytohormone biosynthesis and signaling genes confirm the critical roles of auxin and GA in fleshy fruit initiation. Further, the endosperm tissue was found to play a more prominent role than embryo in the biosynthesis of auxin and GA for fruit initiation. In addition, we examined genes specifically expressed in the receptacle, whose development and enlargement is unique in strawberry. Both receptacle-specific protein coding genes and miRNAs were identified and the functions of these genes are being determined. Our studies are beginning to reveal the molecular underpinnings of early stage fruit development. Insights into early stage fruit initiation have laid the foundation for investigations into mechanisms underlying morphological diversity of different Rosaceae fruits.