MADS-Box Genes are Involved in Cultivar- and Temperature-Dependent Formation of Multi-pistil and Polycarpy in Prunus avium L.

The frequent occurrence of polycarpy is the most serious problem directly compromising sweet cherry productivity in warm regions of the world. MADS-box genes play an important role in regulating the pistil development; however, limited evidence is available for understanding the regulatory mechanisms of MADS-box genes underlying multi-pistil formation in sweet cherry. In our study, we found that the multi-pistil occurred more frequently in the warm region of Shanghai than the cool region of Dalian. Particularly, the multi-pistil rate of ‘Tieton’ reaches 80–90%, which is much higher than that of ‘Lapins’ with 20–30% in Shanghai. PaAG, PaTM6 , and PaMADS3/4/5/12 were found to be sensitive to different natural temperatures related to the formation of multiple pistils according to the quantitative real-time PCR assay. Moreover, the heat shock element in the promoter of PaMADS12 was identified. Using the GUS histochemical assay, we found that the expression level of the β-glucuronidase in the transgenic N. benthamiana leaves containing the GUS reporter gene driven by the PaMADS12 promoter was much higher at 35 °C than that at 25 °C. This suggested that PaMADS12 is a heat-induced transcription factor functioning in multi-pistil formation. Together, these results indicated that heat induced the expression of PaMADS12 , and PaAG, PaTM6 , and PaMADS3/4/5/12 were important components of the regulatory network controlling multi-pistil formation in sweet cherry.