Complex pathways control the shape of plant cells

US researchers have mapped a series of pathways that control the shape of plant cells, in what could be an important step towards customising how plants grow to suit particular agronomic needs.

Cotton production is a $25 billion industry in the United States, but the types of cotton that farmers can grow is of lesser quality than premium Egyptian or Pima cottons, which have smaller fibre diameters. Professor Daniel Szymanski from Pursue University used the model plant Arabidopsis to analyse how intracellular signalling networks pattern cell walls to generate particular cell shapes and sizes. This knowledge can be used to generate cotton fibre cells with smaller diameter or increased strength.

Writing in the journal Current Biology, Professor Szymanski and his colleagues described how microtubules and actin — protein polymers that form the cytoskeletons of plant cells — are organised to specify the mechanical properties of cell walls that define cell shape. The group found that microtubules entrap a protein called SPIKE 1 within the apex of a cell where SPIKE 1 recruits additional protein machineries that cause actin filaments to form. Actin filament networks are then organised as roadways for long-distance intracellular transport and the regulated delivery of cell wall materials that are necessary for cell growth.

“SPIKE 1 is a master regulator in cells; a switch that when activated determines the time and location where actin networks are polymerised,” Professor Szymanski said.

The location and activity of SPIKE1 is important, the study found. Without it, growth is misregulated, leading to distorted cell shapes that do not taper properly. The protein is thus one of a growing number of tools that could be used to program the size and shapes of economically important cells, including cotton fibres.

According to Professor Szymanski, this new understanding will also likely play a broader role in designing plants that have different cell shapes and sizes. He said, “Cells are building blocks for tissues and organs, and they have the potential to influence key traits like leaf size. This work provides a knowledge base that will enable cell, tissue and organ engineering.”

Image caption: Daniel Szymanski used the model plant Arabidopsis (in his hand) to map the complex pathways that control plant cell shape. The findings may be key to improving the quality of cotton (in the background) grown in the United States. Image credit: Purdue Ag Communication/Tom Campbell.