Search

Oryza meyeriana is highly resistant to rice bacterial blight (BB) and this resistance trait has been transferred to cultivated rice (O. sativa) using asymmetric somatic hybridization. However, no resistance genes have yet been cloned. In the present study, a progeny of the somatic hybridization with high BB resistance was crossed with a rice cultivar with high BB susceptibility to develop an F2 population. Using bulked segregant analysis (BSA), 17 polymorphic markers that were linked to rice BB resistance were obtained through scanning a total of 186 simple sequence repeats (SSR) and sequence-tagged site (STS) markers, evenly distributed on 12 chromosomes. A genetic linkage map was then constructed based on the 17 linkage markers and the F2 segregating population, which was followed by mapping for quantitative trait loci (QTLs) for BB resistance. Three QTLs were identified on chromosomes 1, 3 and 5, respectively, and the alleles of the resistant parent at any of the QTLs increased BB resistance. All of the three QTLs had a strong effect on resistance, explaining about 21.5%, 12.3% and 39.2% of the resistance variance, respectively. These QTLs were different from the loci of the BB resistance genes that have been identified in previous studies. The QTLs mapped in this work will facilitate the isolation of novel BB resistance genes and their utilization in rice resistance breeding.

Lesion mimic mutants (LMMs) are plants that spontaneously form lesions without pathogen infection or external stimulus and exhibit resistance to pathogens. Here, a rice LMM was created by ethyl methane sulfonate mutagenesis, named as hpil (hydrogen peroxide induced lesion). Diaminobenzidine and trypan blue staining showed that large amounts of H2O2 were produced and cell death was occurred at and around the parts of lesion mimic in the rice leaves. The phenotype of hpil is controlled by a single recessive gene, localized at a 2 Mb interval on chromosome 2. The data suggested that hpil is a novel LMM with enhanced bacterial and fungal disease resistance, and multiple pathogenesis-related proteins (PRs) were up-regulated. The proteomes of leaves at three positions (different degrees of lesion mimic severity) were characterized in hpil compared with its wild type plant. Differentially expressed proteins were detected by two dimensional difference gel electrophoresis and 274 proteins were identified by MALDI TOF/TOF™. These proteins were related to metabolic process, cellular process and response to stimulus, with mostly down-regulated in hpil leaves. Many of these proteins were related to the Calvin cycle, photosynthetic electron transport chain, glycolysis/gluconeogenesis and phosphonates pathways. Some resistance-related proteins including 14-3-3 proteins, OsPR10 and antioxidases such as peroxidase, superoxide dismutase and ascorbate peroxidase were up-regulated in leaves with lesion mimic. These results provide the foundation for cloning of the target gene and shed light on the mechanism involved in autoimmunity of rice.