Trapping signal proteins through snares
Plant growth is an exceptionally complex process relying on the correct molecular signals in both time and space. When a cell extends and grows, its internal supporting skeleton must provide a precisely positioned framework. Furthermore, the signalling mechanisms in play must modulate chemical trafficking on the cell membrane. The EU-funded 'Studying plant cell secretion and membrane trafficking' (Cellsec) project investigated the action of two proteins in this web of interlinked pathways in polar growing cells. Polar growth is where extension is confined to a small part of their surface area. Prior to Cellsec, little was known about the action of spindle assembly checkpoint (SAC) and syntaxin, a so-called soluble NSF attachment protein receptor (SNARE) protein. SAC proteins are involved in activating many of the chemical cascades in the growth process. Syntaxin proteins play a major part in exocytosis, the process whereby small sacs (vesicles) of soluble chemicals are released from the cell membrane. Syntaxin is involved in the docking and fusion of the sacs with the cell membrane. This provides a mechanism for regulating membrane secretion in growth. Using mutant studies, the Cellsec team showed that although syntaxins are required, they do not provide the level of specificity required. This is provided by other signallers like calcium ions and the expression of a gene, PIP5K4. Expanding on the role of calcium ions in the environment, the scientists investigated the associated role of the genes for the so-called cyclic nucleotide gated channels (CNGCs). These cunning molecules respond to changes in charges on the cell membrane and so provide an 'electrical' switch for chemical processes. Sexual reproduction is at the heart of the creation of genetic variety in plants. As pollen tube growth is a crucial stage in plant sexual reproduction, the Cellsec research will be of interest to plant breeders and agro-industrial companies.
