GENES INVOLVED IN THE CONTROL OF GROWTH AND DIFFERENTIATION IN PLANTS

The mechanisms underlying totipotency, the unique ability of isolated plant cells to regenerate into plants, offer developmental biology a u nique challenge. While it has been recognised for some time that phyto hormones, such as auxin and cytokinin, play a role in this process by inducing a variety of growth patterns in both isolated cells, unorgani sed callus and intact plants, the molecular basis of their action rema ins unknown. The molecular and biochemical analysis of the novel inter action between tumour-inducing soil bacteria and the wounded plant has provided a valuable insight into how plants respond to phytohormones. During tumour formation, the bacteria transfer to the genome of the h ost plant a variety of genes which either short circuit the normal pat hways of accumulation of phytohormones or modify how the plant cell re sponds to them. In parallel to these studies, we have been investigati ng plant genes involved directly or indirectly in the mechanism of phy tohormone action. Auxin-binding proteins (putative receptors) have bee n localised in various cellular locations and the genes encoding them are currently undergoing analysis. Recently, a novel form of T-DNA has been devised by which mutant plant cell lines can be generated which grow in culture in the absence of exogenously applied auxin. The tagge d genes, which are in effect plant cellular proto-oncogenes, are likel y to shed more light on how auxin serves to regulate growth and develo pment.