Abstract: 【Objective】A rice mutant, dwarf and deformed flower 2 (ddf2) , was characterized in the present paper. These results will provide a foundation for map-based cloning and functional analysis of the DDF2 gene. 【Method】 The ddf2 mutant was derived from tissue culture mutation generations of indica restorer 602. At the heading stage, the plant height, panicle length, width and length of leaves and internodes of the ddf2 mutant and wild type were measured. Moreover, the phenotype and histology analyses of stem, leaf and spikelet were conducted. A population containing 1 024 F₂ mutants from the zhonghua11/ddf2 cross was used to map the DDF2 gene. The expression of candidate genes were detected by real time PCR. 【Result】 The leaves and internodes of ddf2 mutant were all much shorter and thinner than those of the wild type, and the panicleof ddf2 mutant was shorter than that of the wild type. According to the histology analysis, the width between two large veins of leaf was decreased dramatically in ddf2 mutant, while no obvious difference in the numbers of large and small veins was observed between the ddf2 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 the number of vascular bundles 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. Additionally, the 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. Genetic analysis indicated that ddf2 was a nuclear recessive gene. By using 1 024 F₂ mutants from the zhonghua11/ddf2 cross, 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 distance of 0.049 cM and 0.098 cM, respectively, and an approximate physical distance of 90.295 kb. 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 qRT-RCR, it was found that the expression of LOC_Os11g17600, encoding an exocyst complex component Sec3_C protein, was down regulated in the ddf2 mutant. Then, the LOC_Os11g17600 was considered as candidate gene of DDF2.【Conclusion】DDF2 is considered to be a novel gene controlling both stem, leaf and floral organ development.

Key words: rice (Oryza Sativa), dwarf, floral organ, dwarf and deformed flower 2 (ddf2), gene mapping