Morphological Characteristics And Genetic Mapping Of An Increased Stigma Mutant In Rice

The development of flower are the most obvious characteristics of flowering plants at growth stage, the process of floral organ is one of the important genetic characteristics. Rice is one of the most important food crops in the world, rice production and quality depend on the development of the floral organ. Study the mechanism of genic regulation will contribute to the development of molecular breeding of rice. As a gramineal model plant and a delegate of monocotyledon, genetic and molecular mechanism underlying the regulation of the rice floral organ development had become a hot spot of plant developmental biology. At present, most genes were isolated by screening the cDNA or DNA library with the probes homologous to sequences of dicot plants, and their functions were identified by the morphology of floral organs in transgenic plant. But the method limited greatly the understanding of the regulation on floral development. The mutant of rice floral organ was important for gene cloning and the studies on gene expression and its function. Research on rice reproductive mechanism has significant theory worthiness. With molecular biology techniques of rapid development, floral organ mutants are increasingly being identified by the cloning of new genes on the increase in the quantity and gene regulation function of depth have been cloned, it may eventually change the rice flower development through means of genetic engineering, and achieve high yield and quality purposes.A rice floral mutant was isolated from the progenies of the combination of C2/Mianxiang2480B.Floral malformed structures and its morphogenesis were identified by anatomical microscopy, paraffin slics, scanning electron microscopy and genetic analysis of mutant traits, furthermore, related genes were preliminary molecular mapped. Main results were as below:1. Compared with wild type, the mutant showed dwarf plant-height, small panicle, the flag leaf curled and tied at the adaxial part, smaller grain, somne narrow and crescent Chaffs are not closed, and flowering time significantly later than wild-type rice. Most of florets were made up of normal lodicule, increased stigma, more pistils, fewer stamens. Anatomy microscope results showed that 58% of them are many stigma, 29% of them are displayed stamen—origin pistils , 25% of them are the twin ovarys, 75% of them are abnormal anthers.2. The wild type and mutant were not different significantly at the beginning of floral primordium differentiation by SEM. But their appearance were obviously different at the beginning of stamen primordium. Wild-type into the pistil and stamen differentiation stage, spikelet primordium will conduct a balanced split, eventually to form six equal stamens arranged a Concentric circles around the pistil. In mutant type florets, the stamen development was at the different stage. Two stamen primordiums at the cross of lemma and palea developed firstly, and outward on both sides of the intersection to extrusion, showing the way with oval. At the same time, spikelet primordium is unequal division, ranging the number of stamen primordiums, showing non-concentric circles.3. Three F₂ groups separately plant, the segregation ratio of wild type plants to mutant plants in the population was accorded with 3:1. It indicated that the mutant was controlled by a single recessive gene.4. Polymorphisms between mutant and T116, with 512 pairs of SSR primers. The polymorphic markers were subsequently used to survey in a small population including the 2 parents, 4 wild type F₂ plants and 6 mutant F₂ plants. Results showed that 4 SSR markers RM162, RM6838, RM3183 and RM3827, located on chromosome 6, were obviously associated to the mutant phenotype. Those 4 markers were then utilized to survey all 92 mutant plants which come from the mutant×T116 in the same F₂ population. Thus, RM162,RM6838 and RM3183 were verified to be linked to mutant gene on one side, with genetic distances of 10.9CM,5.4CM and 2.2 CM, respectively, and another marker RM3827 were verified to be linked to mutant gene on the other side, with genetic distances of 12.0 CM, respectively.5. According to the ABC model of floral organ, the traits were changed in the third and forth whorls of the mutant type florets. We deduced that the phenomenon of twin-ovary and more stigmas in the forth whorls were from partly homeotic conversion of stamens into pistils. It was very similar to the phenotype for loss of B functional genes in Arabidopsis. Simultaneously, the mutant had malformation embryo sac and two ovules in the same ovary, which implied that D functional genes were included.