The Transcription Repressor Regulates Cell and Fruit Size in Apple Fruit.

Auxin plays an important role in regulating plant development, and () is a type of auxin-responsive gene and plays an important role in auxin signaling; to date, although 29 Aux/IAA proteins have been reported in , only parts of the family gene functions have been identified. We previously reported that a bud sport of 'Longfeng' (LF) apple (), named 'Grand longfeng' (GLF), which showed a larger fruit size than LF, has lower expression of . In this study, we identified the function of the gene in apple fruit size difference using -mediated genetic transformation. Overexpression of decreased the apple flesh callus increment and caused a smaller globular cell size. In addition, overexpression of in GLF fruit resulted in the reduction of apple fruit size, weight, and cell size, while silencing in LF apple fruit resulted in an increase in apple fruit weight and cell size. We suggest that the high auxin content depressed the expression of , and that the downregulated expression of led to the formation of GLF. Our study suggests a mechanism for fruit size regulation in plants and we will explore the transcription factors functioning in this process in the future.