Abstract: Phi thickenings are peculiar secondary cell wall thickenings that form reinforcing bands around the radial walls of cortical cells in plant roots, a location where only a primary cell wall would normally be found. These thickenings are widespread in the plant kingdom, being present in the roots of taxa as diverse as epiphytic orchids, gymnosperms, apples and Brassica. It has been suggested that the thickenings help to mechanically stabilise the growing root tip. However, research into their development and function has been lacking, partly because of a lack of suitable models.

We have demonstrated that phi thickenings are rapidly induced In Brassica primary roots in response to both osmotic stress and to mechanical stimulation of the root's surface. Moreover, both pathways are transduced by the stress hormone jasmonic acid. This rapid induction system not only provides a tool with which the functions of these enigmatic structures might be clarified, but has been used to investigate the induction of phi thickenings at a genetic level. In collaboration with the NSW Department of Primary Industry, the molecular development of phi thickenings has been studied in Brassica breeding populations and through genome wide association studies (GWAS) in B. napus. A potential phi thickening developmental mutant has been uncovered, and candidate genes associated with QTLs linked to the phi thickening developmental pathway have been identified.

Biography: Following an undergraduate degree at Sydney University and a PhD in the old RSBS at ANU, David completed postdoctoral positions in the Netherlands, Japan and the USA and then spent 5 years as an ARC Research Fellow back at RSBS. After his PhD and post-doctoral work which focused on the structure and functions of the cytoskeleton in plants, his research since taking a faculty position at the University of Canterbury in Christchurch in 2008 has focused on the plant cell wall, predominantly in Arabidopsis and orchids. However, extensive collaborations with Canterbury's Forestry School involved investigations of cell wall development in commercial species such as radiata pine, eucalyptus and mahogany. In 2016, David moved to the University of Newcastle and established a new research group that targeted a specific class of plant cell wall, the phi thickenings of the root cortex. This research has used the Brassica primary root as a model system for both cell and molecular genetics investigations of these enigmatic structures. More recently, with his wife having been appointed to the University of Canberra, he has joined RSB as a visitor