Functional genomic approaches in cereal rusts

Cereal rust fungi are pathogens of major importance to agriculture, threatening cereal production worldwide. Targeted breeding for resistance, based on information from fungal surveys and population structure analyses of virulence, has been effective. Nevertheless, breakdown of resistance occurs frequently and continued efforts are needed to understand how these fungi overcome resistance and to determine the range of available resistance genes. The development of genomic resources for these fungi and their comparison has released a torrent of new ideas and approaches to use this information to assist pathologists and agriculture in general. The sequencing of gene transcripts and the analysis of proteins from haustoria has yielded candidate virulence factors among which could be defence-triggering avirulence genes. Genome-wide computational analyses, including genetic mapping and transcript analyses by RNA sequencing of many fungal isolates, will predict many more candidates. Functional assays, such as leaf infiltration using Agrobacterium for delivery of cloned fungal effectors, are being developed. This will allow the screening of wheat germplasm for novel resistance genes for breeding. Comparative analyses have also revealed fungal virulence genes, providing fungal targets for disease control in host-produced RNAi approaches.