| Rice is a leading cereal crop and staple food for over half of the world population. Tillering in rice is one of the most important agronomical traits that determine grain yield. Meanwhile, tillering in rice is also of developmental importance because tiller is a special type of branching, which is quite different from that of dicotplants. Therefore, it is significant in theory and valuable in production to investigate the mechanism of tillering. Identification and isolation of new tillering genes will help to investigate plant molecular biology mechanism of branching which could be applied in rice breeding to improve the field per unit via controlling the tillering number of rice plants and populations.Two rice mutants, mt1-1and mt1-2, characteristic of strong-tillering, were found in the progeny of Zhonghua 11 that was treated with 0.1 %EMS. Two mutants have several major features: fast tillering, profuse tillers, dwarf, and narrow leaves. Genetic analysis indicated that the mutated tillering trait was controlled by a recessive gene.In order to clone this multiple-tillering gene, F2 progeny of mt1-1//Dular were used to fine map this recessive multiple-tillering gene.It was roughly mapped on chromosome 1 of rice between two microsatellite markers SSRl49 and RM297, with genetic distances 0.80cM of and 3.l0cM, respectively.Compared with the known linkage map of rice, it could be inferred that the mutated tillering gene is situated on the long arm of chromosome 1 of rice. So far there has been no similar gene site reported on this region. It indicates that this is the first report of the two kind of gene here. Therefore, the gene is temporarily designated as MT1(MUTIPLE-TILLERING1).Then according to the known genomic sequences, four new polymorphic microsatellite markers, SSR-1-27 ,SSR-1-24, SSR-mt3 and SSR-mt4, which are between RM297 and SSRl49, were developed for fine mapping. And the MT1 gene was further mapped between two microsatellite markers SSR-1-24 and SSR-mt4 with the genetic distances of 0.18cM and 0.03cM, respectively. Based on the above information, a BAC contig , AP003376, was found to span MT1 locus, the region being delimited to about 30kb.Nucleotide sequence analysis showed that a gene encoded a protein which was 68% identical to Arabidopsis thaliana MAX4 (MORE AXILLARY GROWTH4)/CCD8. Therefore, PCR (Polymerase Chain Reaction) was employed to amplify this gene sequence from wild type Nipponbare and the mt1 mutants DNA. Sequencing analysis indicated that in the mt1-1 mutant, the MT1 gene had a deletion of 278bp at the start codon ATG site of the gene, which led to no protein being translated, while a 16bp sequence was inserted in the second exon in the mt1-2 mutant. Subsequently, complementary test was employed to prove our result. To transform a DNA fragment of full length MT1 gene to mt1-1 mutant, the tillering character of the transplants was recovered. It indicated that this gene was the actual gene MT1 which controlled the strong branching of rice. Additionally, a pilot study was done to analyze the expression of this gene here.
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