| Rice is an important stable crop worldwide. Although it’s vegetative organs and floral organs are not the final production organs, their development has important influence on productiom and quality of grain. Therefore, the studies of the key regulatory genes’ function on these rice organs also have great significance to high yield and quality breeding.A rice mutant, dwarf and deformed flower 2 (ddf2), was characterized in the present paper, deriving from tissue-culture generations of indica restorer 602. At the heading stage, the plant’s height, panicle length, width and length of leaves and internodes were measured in the ddf2 mutant and the wild type. Moreover, the phenotype and histology analysis of stem, leaf and spikelet were conducted. A population contained 1,024 F2 mutants from the Zhonghualllddf2 cross was used to map the DDF2 gene. The expression of candidate gene was detected by real time qPCR. The main results are as follows:1.Phenotypic identification of ddf2Compared with the wild type, the ddf2 displayed dwarfing trait since jointing stage. At heading stage, ddf2 plants’height is only 57.71%. The length and width of first leaf, second leaf, third leaf as well as each internode in dd/2 mutant were all much shorter and thinner than those in the wild type. In addition, the panicle in ddf2 mutant is 15.55cm, was shortened significantly. These results indicate that the size of mutant’s leaf and stem is smaller than wild type.2. Histological analysis of stems and leavesAccording to the histology analysis, the width between two large veins of leave was decreased dramatically in ddf2 mutant, while no obvious difference in the numbers of large and small veins were observed between the ddf1 mutant and the wild type. Further analysis showed that the size and number of mesophyll cells in ddf2 leaves were all reduced significantly. Furthermore, parenchyma cells were significantly reduced in size and number in ddf2 stems, while there was no difference in number of vascular bundle in stem between the ddf2 mutant and the wild type. These results indicated both the cell division and cell expansion were inhibited in ddf2 leaves and stems.3. Floral morphology analysisThe spikelet and floral organs in ddf2 mutant display serious defects. In ddf2 florets, the lemmas were distorted while the paleas were degraded in whorl 1. The stamens were degenerated seriously or transformed into pistil-like organs in whorl 3. Elongated sterile lemma and extra florets were often observed in some ddf2 spikelets.4. Genetic analysisDue to ddf2 unable to produce normal seed, the mutation was maintained only by DDF2/ddf2 heterozygotes. XinonglA and Zhonghuall was crossed with the DDF2/ddf2 heterozygote for for genetic analysis. Both of the F1 progenies represented normal. In the F2 progenies, for the combinations of XinonglAlddf2 and Zhonghua11/ddf2, the plants could be classified as two groups according to the phenotype has no significant difference with the ratio of 3:1. Genetic analysis indicated that ddf1 was a nuclear recessive gene.5. Fine mapping of gene DDF2 and candidate genes analysisBy using 1,024 F2 mutants from the Zhonghua11/ddf2 cross, through the BSA method, the DDF2 gene was mapped between In/Del markers S-11 and S-14 on the short arm of chromosome 11 near the centromere, with genetic distances of 0.049cM and 0.098cM, respectively, and an approximate physical distance of 90.295kb. The gene was co-segregating with another In/Del marker S-24. There were 12 MSU annotation genes within the mapping region. Based on the real time qRCR, we found that the expression of LOC_Os11g17600, encoding exocyst complex component Sec3_C protein, was down regulated in the ddf2 mutant. Then, the LOC_Os11g17600 was considered as candidate gene of DDF2. |
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