When faced with attack by disease-causing organisms, plants rely on an elaborate surveillance system that detects pathogens and triggers a battery of defences to protect the host. Recent studies on the DNA of plants have uncovered an extensive collection of genes that direct this recognition of harmful organisms. These disease resistance genes (R genes) are present in hundreds to thousands of copies, and generally reside in large clusters on the plant genome. SurprisingIy, all of these R genes possess regions of similar DNA sequence that encode highly-conserved
protein structures essential for effective plant defence. Despite this similarity,
different genes can provide resistance to pathogenic organisms as diverse as
bacteria, viruses, fungi and nematodes (see our background story in the January
2001 issue of The Australian Cottongrower). In earlier work we successfully cloned a
small selection of R gene-like DNA sequences, known as resistance gene analogues
or RGAs, from cotton. In this project we proposed to extend the existing work, and as
a result we have now targeted the two major classes of R-genes in plants (NBS-LRR
and STK types). We also proposed to characterise these different genes, and have
attempted to link DNA polymorphism within the genes with Verticillium disease resistance in Australian cotton cultivars.