Identification of Long-Distance Mobile mRNAs Responding to Drought Stress in Heterografted Tomato Plants

Grafting is widely used as an effective strategy to enhance tolerance to biotic and abiotic stresses and improve fruit quality in horticultural crops. However, the molecular mechanisms of transcription and the regulatory functions in response to drought stress of mobile mRNAs remain poorly understood. In this study, we developed a grafting system based on the "one grafted plant-three samples" approach using the cultivated tomato/Solanum pennellii (Heinz 1706/LA 0716) heterografting system. A bioinformatics pipeline was developed based on RNA-seq to identify mobile mRNAs in the heterografting systems. A total of 61 upwardly and 990 downwardly mobile mRNAs were identified. Furthermore, we found that the mobility of mRNAs was not correlated with their abundance. The functional annotation and enrichment analysis indicated that mobile mRNAs were mainly involved in RNA binding, photosynthesis, photosystem, response to heat, and translation processes, and ultimately increased the drought tolerance of grafted plants. In addition, we also analyzed the RNA-binding proteins (RBPs) of downwardly mobile mRNAs and found that RBPs were conserved among species. Further, mobile mRNAs may be degraded during transportation. This study provides a pipeline for detecting mobile mRNAs in plant heterografting systems and offers new insights into future studies on long-distance mRNAs transport and regulatory mechanisms involved in drought stress responses.