Movement of ACC oxidase 3 mRNA from seeds to flesh promotes fruit ripening in apple.

Xenia, the phenomenon in which the pollen genotype directly affects the phenotypic characteristics of maternal tissues (i.e., fruit ripening), has applications in crop production and breeding. However, the underlying molecular mechanism has yet to be elucidated. Here, we investigated whether mobile mRNAs from the pollen affect the ripening and quality-related characteristics of the fruit using cross-pollination between distinct Malus domestica (apple) cultivars. We demonstrated that hundreds of mobile mRNAs originating from the seeds are delivered to the fruit. We found that the movement of one of these mRNAs, ACC oxidase 3 (MdACO3), is coordinated with fruit ripening. Salicylic acid treatment, which can cause plasmodesmal closure, blocks MdACO3 movement, indicating that MdACO3 transcripts may move through the plasmodesmata. To assess the role of mobile MdACO3 transcripts in apple fruit, we created MdACO3-GFP-expressing apple seeds using MdACO3-GFP-overexpressing pollen for pollination and showed that MdACO3 transcripts in the transgenic seeds move to the flesh, where they promote fruit ripening. Furthermore, we demonstrated that MdACO3 can be transported from the seeds to fruit in the fleshy-fruited species tomato and strawberry. These results underscore the potential of mobile mRNAs from seeds to influence fruit characteristics, providing an explanation for the xenia phenomenon. Notably, our findings highlight the feasibility of leveraging diverse pollen genomic resources, without resorting to genome editing, to improve fruit quality.