Speaker: David Jackson, Cold Spring Harbor Laboratory professor

Title: "Trafficking of developmental mRNAs through plasmodesmata- the how and the why"

Abstract: Plant development relies on pools of stem cells that are maintained through activity of the KNOTTED1 (KN1) homeobox (KNOX) family transcription factors. These factors act in a non-cell-autonomous manner, and their mRNA and protein are selectively transported between cells via plasmodesmata, membrane-lined nanochannels that mediate the trafficking of a variety of signal molecules between cells. Plants also use messenger RNAs (mRNAs) as mobile signals for long-distance communication. However, the mechanisms underlying mRNA transport are largely unknown. We previously established a screen for evaluating the selective transport of maize KN1 in arabidopsis. Using this screen, we isolated KN1 trafficking defective mutants in Ribosomal RNA-Processing Protein 44 (AtRRP44A), a catalytic subunit of the RNA exosome that participates in the degradation and processing of various classes of RNA in eukaryotes. While cell-to-cell trafficking of KN1 mRNA requires RRP44A, its catalytic activity is not required, suggesting this may represent a moonlighting function. Furthermore, we found that RRP44A can localize to plasmodesmata, and using the MS2 system to label RNAs in vivo, we found that it mediates cell-to-cell trafficking of KN1 mRNA. Our study suggests that RRP44A mediates cell to cell trafficking of homeobox mRNAs through plasmodesmata to control stem cell-dependent processes in plants.

Funding acknowledgement: National Science Foundation

Hosts: Erik Vollbrecht, genetics, development and cell biology (GDCB) professor; Joe Aung, GDCB assistant professor