Phenotype Characterization And Preliminary Gene Mapping Of A Novel Bisexual Mutant Tassel Silk Florets (Tsf1) In Maize

Maize is monoecious plant. It's an ideal system for studies sex determination in maize. While many researches have been done in the molecular basis of sex determination, however, it molecular mechanism bare comparatively lack. We first reported a spontaneous mutant with tassel silk florets 1(tsf1) .It was found from the inbred line ShanDan 9. In order to identify the phenotype characterization and the rule of inheritance of tsf1,we choose the wide type of k12,dan340? crossnd with the tsf1 mutant and structured F2 populations on that basis,we preliminarily gene mapping of the mutant.1. The maize mutant tsf1 is a natural mutant. In flowering stage, the tassel of tsf1 plants were covered by fuzzy silks .the tsf1 characterized by a complete reversal of sex in tassel florets, the staminate tassel florets of tsf1 convert to the perfect florets. Appearance of seed in tassel is typical phenotype of tassel seed mutants, but there is no seed produced in tassel of tsf1 mutant. In wide type plants, one spikelet will initiate two floret primordiums, upper floret and lower floret, and the lower floret will abort in late stage of ear development. Some of lower florets don't degenerate in the ear of tsf1 plants. From the picture taken by SEM, we can find non-degraded lower florets easily. Additional, one or two irregular branches can be observed generally at the base of ear in tsf1 plant.2. We further analyzed the pollen viability of mutant plants. Based on investigation of TTC staining, the pollen viability of wide type and tsf1 is 98% and 89.26% respectively. It looked that the pollen of tsf1 have lower viability, but about 90 percent of pollen still are fertility. So, we believe that the tassel pistils of tsf1 are sterile, although the tassel was covered with fuzzy silk.3. To understand the genetic behavior of the tsf1 phenotype, Two F2 population (the mutant line tsf1 crossed with the wild type line k12 or dan340) were constructed and the flower patterns of 627 individuals were investigated in the field for genetic analysis. The segregation ratio between mutants and normal individuals of the two F2 populations indicate that the tsf1 phenotype was controlled by a single recessive gene. 4. Polymorphism of 106 SSR markers were detected between the DNA pools of tsf1 and wide type plants, PCR amplification and electrophoresis detection showed that only 5 pairs of them tsf6-13, tsf6-25, tsf6-35, tsf6-10,zag1 were polymorphic between the two parents. The gene tsf1 was located on chromosome 6 between SSR markers zag1 and tsf6-35, which linked to tsf1 with the genetic distances of 4.2 and 5.4cMThis study analyzes the phenotypic differences of tsf1 and other known bisexual mutant, cleared that tsf1 was controlled by a pair of recessive gene which located on chromosome six long arm. This gene located between zag1 marked by SSR and tsf6-35, and the result are contributed for the map-based cloning of tsf1.