The concept that proteins and small RNAs can move to and function in distant body parts is well established. However, non-cell-autonomy of small RNA molecules raises the question: To what extent are protein-coding messenger RNAs (mRNAs) exchanged between tissues in plants? Here we report the comprehensive identification of 2,006 genes producing mobile RNAs in Arabidopsis thaliana. The analysis of variant ecotype transcripts that were present in heterografted plants allowed the identification of mRNAs moving between various organs under normal or nutrient-limiting conditions. Most of these mobile transcripts seem to follow the phloem-dependent allocation pathway transporting sugars from photosynthetic tissues to roots via the vasculature. Notably, a high number of transcripts also move in the opposite, root-to-shoot direction and are transported to specific tissues including flowers. Proteomic data on grafted plants indicate the presence of proteins from mobile RNAs, allowing the possibility that they may be translated at their destination site. The mobility of a high number of mRNAs suggests that a postulated tissue-specific gene expression profile might not be predictive for the actual plant body part in which a transcript exerts its function.
Plants count on a wide variety of metabolic, physiological, and developmental responses to adapt their growth to variations in mineral nutrient availability. To react to such variations plants have evolved complex sensing and signaling mechanisms that allow them to monitor the external and internal concentration of each of these nutrients, both in absolute terms and also relatively to the status of other nutrients. Recent evidence has shown that hormones participate in the control of these regulatory networks. Conversely, mineral nutrient conditions influence hormone biosynthesis, further supporting close interrelation between hormonal stimuli and nutritional homeostasis. In this review, we summarize these evidences and analyze possible transcriptional correlations between hormonal and nutritional responses, as a means to further characterize the role of hormones in the response of plants to limiting nutrients in soil.
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