PHR-Mediated Pi Starvation Response Mobile Messenger RNAs Represent Noncoding Transcripts in Recipient Tissues.

Nutritional deficiency for phosphate (Pi) or nitrogen triggers long-distance transport of specific mobile mRNAs, but little is known about the underlying regulation, function, and structural features of these mobile nutrient starvation-specific mRNAs. Here, heterografting and high-throughput sequencing are used to explore the landscape of long-distance mRNA transport in Arabidopsis under normal and Pi-starvation conditions. Hundreds of Pi starvation response (PSR)-specific mobile mRNAs are discovered, although their abundance is constant between normal and Pi starvation conditions. The mobility of these PSR-specific mobile mRNAs is largely dependent on PHOSPHATE STARVATION RESPONSE (PHR) function, based on mutant analysis. Notably, translatome analysis and transgenic experiments reveal that these PHR-mediated PSR-specific mobile mRNAs are translated in donor tissues, but not in recipient tissues. Further, these mobile mRNAs harbored a more unfolded 5' UTR than nonmobile mRNAs, non-PSR-mobile mRNAs, and nitrogen starvation-response mobile mRNAs. The study reveals that these PSR-specific mobile mRNAs are transported to recipient tissues to carry out a function independently of their encoded protein.