Genetic Identification Of A Dwarf Mutant K123d In Maize

Plant height is one of the important agronomic traits of crops, shorter stalk resources are the material basises of crop dwarf breeding. Dwarf has widely been applied to improve the lodging resistance and to breed the ideal plant type in crops, hence increase the crop yield. So expioring dwarf resources and studying its genetic characteristics and mechanism of dwarf clearly were important for plant breeding and application in production. The objective of this study was to compare the differences of main agronomic traits and sensitivity to the gibberellins between the wild type and dwarf mutant K123d derived from the inbred line K123 via spontaneous mutation. Genetic mating design was made by using K123d and 3 inbred lines with different plant height to analysis the genetic model of dwarf trait. SSR primers were used to locate the target gene. Target gene was cloned and the relationship between target gene and the known dwarf was clarified for laying the foundation for further study and application. The main results were as follows:1. Compared with wild type K123, maize dwarf mutant K123d had shortened stem internode,35.59% lower plant height,35.33% decreased tassel length.15.30% smaller leaf Angle, differences were extremely significant level. It indicated that the more upright leaf and the better plant type of mutant than wild type plants were good for cultivating ideal plant type. But K123d had 28.42% shorter ear length,5.25% decreased ear rows, 45.24% decreased row grains, a 48.22% reduction in grain yield, and the differences of ear length, row grains, grain yield were extremely significant. It indicated that the ear characters of dwarf mutant were poor, remaining to be further improved.2. No embryo seed of K123d and K123 could secrete alpha amylase degradating starch, made the AGAR plate appear transparent hollow after processing by 1 umol/LGA3. It could be infered that K123d was not belong to the gibberellin insensitive type.0,0.1,10,25,50 and 100 mu g/mlGA3 solution were respectively used to water seedling. The results showed that the gibberellin synthesis and transduction pathways of K123d were normal. With the increase of concentration of exogenous gibberellin applied, its endogenous gibberellin content increased significantly, and the seeding height of K123d returned to the wild type. It indicated that K123d is sensitive to gibberellin.3. Genetic mating experiment was carried out by using K123d and 3 inbred lines, which had different plant height. The results showed that the plant heights of F1 and BC2 populations were not segregated, and showed the normal plant. The plant height of BC1 and F2 and were segregated, the segregation ratio of their normal plants and dwarf plants examined by the x2 test were in accordance with the 1:1 and 3:1, respectively. The results indicated that the plant height of mutant K123d was controlled by a pair of recessive nuclear genes. The dwarf gene was temporarily named d123.4. By using K169/K123d-F2 as mapping population,6 pairs of polymorphism SSR markers between parents and F2 gene pool were screened from 583 pairs of SSR markers through bulked segregation analysis(BSA).48 recessive plant DNA of F2 population were amplified by 6 pairs of markers, amplification products were detected with a 6% denaturing polyacrylamide gel electrophoresis. Linkage analysis was done by MAPMAKER3.0. The target gene d123 was preliminary located on maize chromosome 1L between umc1278 and bnlg1564 with genetic distances of 12.8 and 7.3 cM respetively, nearby a known single recessive dwarf gene br2.5. Referencing br2 gene conserved sequence,8 pairs of specific primers were designed by primerer5.0 to clone target gene d123.The target products were recycled and purified to sequencing, the results sequence were joining together and alignment of the br2-like domain in d123 with br2 domain were performed by DNAMAN.The results showed that there were 12 bases substitution between d123 and br2 exons including 11 synonymous mutation bases. Only one mutation, the 531th amino acid on the 4th exon, the glutamate of br2 replaced by lysine of d123 in the same position. All the results demonstrated that the dwarf gene d123 might be one mutation gene derived from br2.