Signaling through Mobile mRNA: Lost in Translation?

Thieme et al. [1] demonstrated that a large population of mRNA is able to travel between plant organs via sieve elements and potentially act as a long-distance signaling molecule [2]. However, a mechanistic basis by which transcripts are selected for transport has not yet been identified. We will present our investigations into possible mechanisms for transport and show that experimental mRNA mobility data in Arabidopsis can be explained by transcript abundance and half-life [3]. This suggests that the majority of identified mobile transcripts can be accounted for by non-sequence-specific movement of mRNA from companion cells into sieve elements [3,4]. Recent results [5] show that a tRNA like motif can influence mobility, leading to the suggestion that this motif is necessary and sufficient to explain mobility. We discuss our abundance hypothesis in light of these new results and critically re-evaluate the current ideas for mRNA transport and function.