micro RNA159-targeted Sl GAMYB transcription factors are required for fruit set in tomato.

The transition from flowering to fruit production, namely fruit set, is crucial to ensure successful sexual plant reproduction. Although studies have described the importance of hormones (i.e. auxin and gibberellins) in controlling fruit set after pollination and fertilization, the role of micro RNA-based regulation during ovary development and fruit set is still poorly understood. Here we show that the micro RNA159/ GAMYB1 and -2 pathway (the miR159/ GAMYB1/2 module) is crucial for tomato ovule development and fruit set. MiR159 and Sl GAMYBs were expressed in preanthesis ovaries, mainly in meristematic tissues, including developing ovules. Sl MIR159-overexpressing tomato cv. Micro-Tom plants exhibited precocious fruit initiation and obligatory parthenocarpy, without modifying fruit shape. Histological analysis showed abnormal ovule development in such plants, which led to the formation of seedless fruits. Sl GAMYB1/2 silencing in Sl MIR159-overexpressing plants resulted in misregulation of pathways associated with ovule and female gametophyte development and auxin signalling, including AINTEGUMENTA-like genes and the miR167/ Sl ARF8a module. Similarly to Sl MIR159-overexpressing plants, Sl GAMYB1 was downregulated in ovaries of parthenocarpic mutants with altered responses to gibberellins and auxin. Sl GAMYBs likely contribute to fruit initiation by modulating auxin and gibberellin responses, rather than their levels, during ovule and ovary development. Altogether, our results unveil a novel function for the miR159-targeted Sl GAMYBs in regulating an agronomically important trait, namely fruit set. [ABSTRACT FROM AUTHOR]