1.Topic: Plasmodesmata, not just Holes in the Wall

Reporter: Dr. Jens Tilsner, Lecturer and Group Leader of University of St. Andrews

Time: 9.00-11.00 a.m., Sep. 5, 2018(Wednesday)

Venue: Room 608, New Yifu Teaching Building, College of Life Science

Abstract

Plasmodesmata (PD) are nanopores that span the plant cell wall and connect the cytoplasm, plasma membrane (PM) and endoplasmic reticulum (ER) of neighbouring cells. They are essential for intercellular communication and domain formation during plant development. PD also serves as signalling hubs during defence responses against invading pathogens, and as conduits for the mobile RNA silencing signal. The permeability of PD is dynamically regulated.  Small molecules such as metabolites and hormones can diffuse through the channels, but macromolecules such as proteins and RNAs are transported between cells in a more specific manner. Despite their importance for plant biology, only few PD components have so far been identified and the mechanisms of their functional regulation remain poorly understood.

The plasma membrane within PD shows distinct features such as a unique protein composition and lack of lateral diffusion. Segregation of PM domains in organisms possessing a cell wall depends strongly on PM-wall interactions. The cell wall around PD is also modified compared to the surrounding ‘bulk’ cell wall. Thus, PD may comprise areas where unique membrane-wall contacts mediate both the PM domain segregation and the specific cell wall architecture that underpin the functional properties of these nanopores.

Additionally, the ER within PD is possibly the most tightly constricted membrane tube found in nature, and connected to the PM by unidentified tethering proteins, which qualifies PD as a unique type of membrane contact site. The extreme biophysical properties of the two PD membranes, and the properties of the PD membrane tethering proteins will be crucial to understanding the molecular basis for cell-to-cell communication in plants.

2.Topic: Push on through to the other Side, a New Hypothesis for how Tobacco Mosaic Virus Gets a few MDa through the Cell Wall

Reporter: Dr. Jens Tilsner, Lecturer and Group Leader of University of St. Andrews

Time: 9.00-11.00 a.m., Sep.13, 2018(Thursday)

Venue: Room 608, New Yifu Teaching Building, College of Life Science

Abstract

Plant viruses are major crop pathogens threatening food security, especially in developing countries. All plant viruses transport their genome from infected to naïve cells through membranous channels called plasmodesmata, in order to spread throughout their host. The virus-encoded proteins mediating this transport have been identified 30 years ago, but the molecular mechanism by which nucleic acid molecules several megadalton in size are transported through the extremely narrow (<10 nm free diameter) channels has not been elucidated. recently, we have shown that the 30k transport protein of tobacco mosaic virus, the first described and paradigmatic plant virus movement protein, forms rna- and membrane-bound polymers that we hypothesize to act as molecular “injection needles” pushing viral genomes through plasmodesmata into uninfected recipient cells.

Bibliography

Folimonova, SY & Tilsner, J 2018, ‘Hitchhikers, highway tolls and roadworks: the interactions of plant viruses with the phloem’ Current Opinion in Plant Biology, vol. 43, pp. 82-88. DOI: 10.1016/j.pbi.2018.02.001

Monsion, B, Incarbone, M, Hleibieh, K, Poignavent, V, Ghannam, A, Dunoyer, P, Daeffler, L, Tilsner, J & Ritzenthaler, C 2018, ‘Efficient detection of long dsRNA in vitro and in vivo using the dsRNA binding domain from FHV B2 protein’ Frontiers in Plant Science, vol. 9, 70. DOI: 10.3389/fpls.2018.00070

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