Rice Genetics IV - IRRI books - International Rice Research Institute

Deletion mutants for functionalgenomics: progress in phenotyping,sequence assignment, and databasedevelopmentH. Leung, C. Wu, M. Baraoidan, A. Bordeos, M. Ramos, S. Madamba, P. Cabauatan,C. Vera Cruz, A. Portugal, G. Reyes, R. Bruskiewich, G. McLaren, R. Lafitte, G. Gregorio,J. Bennett, D. Brar, G. Khush, P. Schnable, G. Wang, and J. LeachA collection of IR64 mutant populations has been established usingdiepoxybutane, fast neutron, and gamma ray mutagenesis. Phenotypic screeningis being conducted on about 12,000 M 3or M 4lines for morphologicalvariations and altered response to biotic and abiotic stresses. About 6% ofthe mutants exhibit morphological variations in the vegetative and reproductivestages. Disease-response mutants are recovered at approximately 0.3%.Based on the frequency of visible and conditional mutants observed underbiotic stresses, the number of mutated sites per genome is estimated to behigh (>10) in these mutants.Mutants are screened for gain and loss of resistance against bacterialblight, blast, sheath blight, and tungro viruses. We have identified mutantswith a gain in resistance to tungro viruses, blast, and bacterial blight. Lesionmimic mutants with enhanced resistance to both blast and bacterial blightare found. To dissect the defense pathways, double disease-response mutantshave been produced to examine the epistatic interactions and expressionprofiles of host defense genes. The mutant collection is being evaluatedfor tolerance of submergence and salinity. Mutants are also being screenedfor altered response under water stress at the flowering stage.Nucleotide-binding site and leucine-rich repeat sequences are used todetect genomic changes in loss-in-resistance mutants; however, the efficiencyof this approach is limited by the number of available candidate genes. Toefficiently assign DNA sequences to mutant phenotypes, we are developinga gene array-based screening strategy using subtractive cDNA/expressedsequence tag libraries enriched for stress-response genes. We are also producingadditional mutant populations to generate a range of deletion sizesthat are suitable for array-based and high-throughput PCR screening. As afirst step, we are using stress-response and morphological mutants withphenotypic and genetic descriptions to develop a mutant database to belinked to sequence databases. We expect the mutant database to grow asthe research community continues to use this mutant resource.Deletion mutants for functional genomics: . . . 239