Benefits of research into MYB5 range from
improving seed crops to tackling male infertility.
Image: iStockphoto

A team of La Trobe University plant scientists led by Professor Roger Parish and Dr Song Li, have identified a missing link in the regulation of seed development. The researchers – whose work will link closely with the new Biosciences Research Centre (see Work starts on $230m Biosciences Centre earlier this year had their study published in the prestigious journal The Plant Cell.

Professor Parish says all seeds have an outer layer of cells – a seed coat that has a protective function. ‘In many seeds this outer cell layer produces mucilage which is secreted into the space between the cell membrane and the outer wall. ‘Upon hydration, the mucilage expands, the cell wall ruptures and a mucilage hydrogel is formed around the seed. This mucilage aids germination by retaining water and is thought to protect seed from infection.’

The La Trobe researchers asked: what controls the formation of this outer cell layer of the seed and the production of mucilage? They discovered a ‘missing link’, a third protein that combines with two other proteins to form a complex essential for seed coat development and mucilage production. Professor Parish explains the newly found protein (MYB5) belongs to the ‘so-called MYB family of transcription factors or “master switches”. The protein complex binds to regions of DNA involved in the turning on and off of genes.

‘When MYB5 protein production is prevented, the cell wall of the seed coat fails to develop normally and mucilage formation is inhibited.’ So what does the MYB5 protein do? In other words, what genes does the complex regulate and what are their functions?

La Trobe researchers have also identified genes whose expression is dependent on the ‘MYB5-complex’.

Novel enzymes

‘These genes,’ says Dr Li, ‘code for two novel enzymes that appear to be required for mucilage synthesis and a further novel enzyme involved in cell wall formation.’

The MYB5-complex also controls the expression of an unusual MYB-like protein that acts as a negative regulator of specific genes. This controls, among other things, the production of anthocyanin pigments responsible for the colours of many fruits and flowers. Their research also found that MYB5 functions as part of a three-protein complex required for leaf hair (trichome) development. Trichomes appear to provide protection against frost and solar radiation and reduce evaporation in windy locations.

The researchers say their work will help provide a better understanding of how plant cell walls are made, and throw light on the way in which mucilage is synthesised.

Mucilage has many practical applications. It is used in food processing as thickening and stabilising agents, and in medicine as demulsifiers.

‘For example, understanding seed coat mucilage and secondary cell wall synthesis will provide opportunities to improve the nutritional value of oilseed crops that are processed for oil and meal,’ Dr Li says. ‘And improving seed quality and germination will add value to grain crops.’ The La Trobe team is also studying a number of other plant MYB proteins, one of which is required for pollen development.

That work has already resulted in a new system for controlling male sterility and the development of a technology for producing hybrid seed. Their laboratory was recently awarded an ARC Linkage Grant to support a collaboration with Pacific Seeds, resulting in total funding of $800,000.