Spotted leaf 5 (spl5), a lesion mimic mutant, was first identified in rice (Oryza sativa L.) japonica cv. Norin8 in 1978. This mutant exhibits spontaneous disease-like lesions in the absence of any pathogens and resistance
to rice blast and bacterial blight; however, the target gene has not yet been isolated. In the present study, we employed
a map-based cloning strategy to finely map the spl5 gene. In an initial mapping with 100 F2 individuals (spl5/spl5) derived from a cross between the spl5 mutant and indica cv. 93-11, the spl5 gene was located in a 3.3-cM region on chromosome 7 using six simple sequence repeat (SSR) markers. In a high-resolution
genetic mapping, two F2 populations with 3,149 individuals (spl5/spl5) were derived from two crosses between spl5 mutant and two indica cvs. 93-11 and Zhefu802 and six sequence-tagged site (STS) markers were newly developed. Finally, the spl5 gene was mapped to a region of 0.048cM between two markers SSR7 and RM7121. One BAC/PAC contig map covering these markers’
loci and the spl5 gene was constructed through Pairwise BLAST analysis. Our bioinformatics analysis shows that the spl5 gene is located in the 80-kb region between two markers SSR7 and RM7121 with a high average ratio of physical to genetic
distance (1.67Mb/cM) and eighteen candidate genes. The analysis of these candidate genes indicates that the spl5 gene represents a novel class of regulators controlling cell death and resistance response in plants.
"The SSCP–SNP assay developed on our HEGS platform is efficient and sensitive to most of the PCR products in the size range of 100–750 bp, requires minimum gel processing time and reasonably high throughput in nature (1,536 SNP data points per person per day) (Xu et al. 2009). Recently, Chen et al. (2009) delimited 80 kb candidate interval for spl5, flanked by SSR7 and RM7121, though this is slightly adjacent to the candidate region identified in the present study for the NF4050-8 causal locus. The 35 kb genomic interval delimited by the highresolution mapping contained seven ORFs, five of which are related to defense response and/or cell death and are considered potential candidate genes for the spl NF4050-8 lesion mimic locus. "
[Show abstract][Hide abstract] ABSTRACT: We evaluated a large collection of Tos17 mutant panel lines for their reaction to three different races of Magnaporthe oryzae and identified a lesion mimic mutant, NF4050-8, that showed lesions similar to naturally occurring spl5 mutant and enhanced resistance to all the three blast races tested. Nested modified-AFLP using Tos17-specific primers and southern hybridization experiments of segregating individuals indicated that the lesion mimic phenotype in NF4050-8 is most likely due to a nucleotide change acquired during the culturing process and not due to Tos17 insertion per se. Inheritance and genetic analyses in two japonica × indica populations identified an overlapping genomic region of 13 cM on short arm of chromosome 7 that was linked with the lesion mimic phenotype. High-resolution genetic mapping using 950 F(3) and 3,821 F(4) plants of NF4050-8 × CO39 delimited a 35 kb region flanked by NBARC1 (5.262 Mb) and RM8262 (5.297 Mb), which contained 6 ORFs; 3 of them were 'resistance gene related' with typical NBS-LRR signatures. One of them harbored a NB-ARC domain, which had been previously demonstrated to be associated with cell death in animals. Microarray analysis of NF4050-8 revealed significant up-regulation of numerous defense/pathogenesis-related genes and down-regulation of heme peroxidase genes. Real-time PCR analysis of WRKY45 and PR1b genes suggested possible constitutive activation of a defense signaling pathway downstream of salicylic acid but independent of NH1 in these mutant lines of rice.
[Show abstract][Hide abstract] ABSTRACT: A lesion-mimic phenotype in rice (Oryza sativa L.) spotted leaf 5 (spl5) indicates that wild-type SPL5 negatively regulates cell death and resistance responses. Previously, the spl5 gene was already mapped to the 80-kb region between two markers SSR7 and RM7121 through a map-based cloning approach. Here, we further showed that the spl5 gene was delimitated into a 15.1-kb genomic region by the high-resolution sequence target site (STS) markers. Subsequent sequencing in this region of spl5 mutant revealed that one candidate gene harbored a single-base deletion, resulting in a frame-shift mutation and a premature stop codon. Bioinformatic analysis showed that SPL5 gene encodes a putative splicing factor 3b subunit 3 (SF3b3) and might be involved in splicing reactions of pre-mature RNAs participating in the regulation of cell death and resistance responses. Further analysis showed that wild-type SPL5 did functionally complement the spl5 phenotype. The data presented here clearly indicate that the SPL5 negatively regulates cell death and resistance responses via modulating RNA splicing in plants.
[Show abstract][Hide abstract] ABSTRACT: A rice lesion mimic mutant, lm3, was obtained by the mutagenesis of an indica cultivar, 93-11, using γ-ray radiation. Brownish lesions appeared on the leaves of lm3 at the young seedling stage and persisted until the ripening stage. The lm3 mutant was characterised by a shorter plant height and delayed heading compared with the wild-type 93-11. A genetic analysis indicated that the lesion mimic phenotype was controlled by a single recessive gene. Using simple sequence repeat (SSR) markers, the target gene LM3 was first located between marker RM5748 and RM14906 on chromosome 3. We then developed Insertion-Deletion (InDel) markers to fine-map LM3, and the locus was localised to a 29 kb region defined by two InDel markers, In12571 and In12600. Five ORFs were predicted in the candidate region, and DNA sequencing detected a single-nucleotide polymorphism (SNP) in the coding region of LOC Os03g21900. The SNP in the fourth exon (C in 93-11; T in lm3) of LOC_Os03g21900 results in the substitution of a proline (P) with a serine (S) at the 140th amino acid of the deduced uroporphyrinogen decarboxylase protein. We did not detect polymorphisms in the other predicted ORF regions between lm3 and 93-11. These results suggest that LOC_Os03g21900 is the most likely candidate gene for LM3.
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