Characterization of FaSPT, a SPATULA gene encoding a bHLH transcriptional factor from the non-climacteric strawberry fruit

The involvement of basic-helix-loop-helix (bHLH) transcription factors in essential physiological and developmental processes is well established. Although a lot of animal bHLH proteins were characterized functionally, much less bHLHs of plant origin have been studied so far. Using a cDNA-AFLP approach, a ripening-related SPATULA gene was identified from strawberry fruit (Fragaria × ananassa Duch.), which encodes a bHLH protein. It is an orthologue of an Arabidopsis SPATULA protein, which has an important role in carpel and fruit development. Our experiments revealed that FaSPT is repressed by auxin in green fruits, and shows different expression patterns in receptacles at various stages of fruit ripening by ethylene treatment. Moreover, we applied a reverse genetic tool to elucidate the in planta function of FaSPT in early fruit development.To our knowledge, this work is the first report for the characterization of a SPATULA gene from a non-climacteric fruit.

Research highlights
► The importance of plant bHLH transcriptional factors in essential developmental processes like stress responses, carpel and epidermal development, fruit dehiscence, anthocyanin biosynthesis, phytocrome signaling is well established.
► In this study FaSPT, a SPATULA gene encoding a bHLH protein was isolated and examined from the non-climacteric strawberry. We studied the regulation of FaSPT in response to auxin and ethylene, moreover we applied a transient-gene silencing assay to down-regulate FaSPT expression in strawberry fruit.
► Our results indicate that FaSPT is an essential transcriptional factor involved in strawberry fruit developmental processes.