| Chloroplast is the energy converter of green plants and it is essential for photosynthesis and the production of chlorophyll, hormones and metabolites. Although chloroplast has its own genome and mechanism of protein synthesis, the majority of proteins needed for chloroplast function are encoded in the nucleus, translated in cytoplasm and then imported into the chloroplast. As a consequence, normal chloroplast biogenesis and development requires exquisite regulation of gene expression between the nucleus, in which many of chloroplast protein components are encoded, and the chloroplast, in which the plastid-derived retrograde signal sent to modulate nuclear gene expression. Perturbation of the coordinated expression of genes between the nuclear and plastid genomes in mutants, leads to abnormal chloroplast development and decreased chlorophyll content. Rice is one of the most important food crops and a model monocotyledon for genomics research. Therefore, it is a value to study chloroplast development and mechanism of photosynthesis by rice leaf color mutants.In this study, a leaf color mutant "wgl58"was isolated from a rice recurrent population treated with EMS. We researched wgl58 by phenotype observation, agronomic traits investigation, physiological characteristics study, genetic analysis and gene mapping. The main results were as follows:1. Compared with the wild type, the leaves of mutant wgl58 appeared distinct white stripes along the vein from early stage to maturity, and showed obviously decreased pigment contents. In addition, the plant height, flag leaf length and width, seed setting rate and 1000-grain weight of mutant wgl58 obviously decreased.2. Mutant wgl58 was a thermo-sensitive mutant. Although the wild type plants showed increased leaf chlorophyll content under 22℃,27℃ and 32℃ conditions respectively, the wgl58 plants showed the lowest relative chlorophyll content, only 36.2% of the wild type, under 22℃ condition. However, it was the highest, up to 72.7% of the wild type, under 32℃ condition.3. The genetic analysis indicated that the mutant wgl58 was controlled by a single recessive gene. The gene was primary delimited to the region between the SSR markers RM3431 and RM3438 on the short arm of chromosome 6. Then, new InDel markers were developed for fine mapping based on the sequence differences between Oryza sativa subspecies indica and japonica and primers were designed based on the flanking sequences of In-Dels. Using the F2 population consisting of 1253 white-stripe-leaf individuals derived from a cross between wgl58 and "02428", the wgl58 gene was delimited to the region between the markers Ch6-819-1 and Ch6-825-1 which physical distance was 64 kb.4. There were 13 candidate genes predicted using the website Rice Genome Annotation Project in the target interval. The function annotation of the 13 candidate genes was conducted. The results indicated that LOC_Os06gl4620 encoded ribonucleotide reductase(RNR) small subunit. RNR is an essential enzyme for chloroplast biogenesis and development. So the gene LOC_Os06gl4620 might control the phenotype of mutant wgl58.5. The sequence of LOC_Os06g 14620 was downloaded from NCBI and 4 pairs of primers were designed using primer premier 5.0 or Primer 3 Input (version 0.4.0). The whole DNA sequence was amplified from the wild type and wgl58 plants respectively. DNA sequencing of LOC_Os06g 14620 revealed that a single-nucleotide change (G511T) occurred in the wgl58, which caused a amino acid mutation, Val to Phe. These results indicated that LOC_Os06g 14620 was the WGL58 gene and it was the allele of stl. But the phenotypes and point mutations of wgl58 and stl were different. The mutation of stl was occurred at the 119 base and its mutant phenotype exhibited at the L4 or L5 stage later than the mutant wgl58. |
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