Fine Mapping Of Yl(t) Gene Using Yellow Leaf Rice Mutant, And Analysis Of Physiological And Biochemical Characteristics Of Six Mutants With Stable High Percentage Of Chalkiness In Rice Grains

Fine Mapping of yl(t) Gene Using yellow leaf Rice MutantThe mutant employed in this experiment is a type of virescent yellow leaves mutant yl(t) which obtained from an rice variety K17B treated by 60Coγ-ray. Mutant leaves show fully yellow colour till trefoilstage and turns green gradually. In order to investigate the mechanism underlyiing the mutant phenotype, we compared development of chloroplast morphology and fluorescence parameters between mutant and its wild type. Futhermore, we finely mapped the locus of Yl(t) to 63-kb region. The main results are as follows:1. Genetic analysis of yl(t) mutant. F2 population was constructed from a cross between yl(t) mutant and Nipponbare. All F1 plants from the cross displayed wild type phenotype, and their F2 progeny showed a separation ratio of 3:1(green: virescent yellow plants,χ2<χ20.05=0.209; P>0.05). Therefore, the phenotype of yl(t) mutant was controlled by a single recessive gene.2. Comparing with wild type, the yl(t) mutant exhibited significantly reduction in total chlorophyll and chlorophyll a, b content without significantly change at the Chla/Chlb ratio. The yl(t) mutant appeared to turn green about 20 days after germination, the pigment content graduate increased, but slightly lower to the level of wild type.3. The results of plastid structures observed by transmission electron microscopy showed that, compared with wild-type, chloroplast in two-leaf-old yl(t) mutant had less well-developed hypoplasia, and fine thylakoid and grana were hardly observed. Even in mature leaves, some chloroplasts in yl(t) were still in decomposition state.4. After construction of F2 mapping population, the yl(t) locus was roughly mapped to a 353-Kb DNA region on the long arm of chromosome 6, and fine mapped the yl(t) locus to a 63-kb region flanked by InDel 26 and InDel 38 markers based on 1381 homozygous mutant plants. Eight genes were included in the region predicted by GRAMENE. However, no sequences and the transcription levels difference was found within these genes between the yl(t) mutant and wild type. It suggests that the virescent yellow leaf mutant phenotype may be caused by some unknown-factor which needed to be found in further research.Analysis of Physiological and Biochemical Characteristics of Six Mutants with Stable High Percentage of Chalkiness in Rice GrainsChalkiness is an important quality character in rice, which is affected by comprehensive effects of genetic and environmental factors. Here, we used six stable severe chalky mutants to analyze the fluctuation of the key enzyme activities associated with starch synthesis, sucrose content, starch content, and the ratio of amylose to total starch in mature grains. The results suggest that physiological studies of grain development are essential to reveal the formative mechanism of chalky rice. The main results were as follows.1. To screen stable high percentage of chalkiness mutants, the T-DNA insertion mutant pool of cultivar Nipponbare was planted in Beijng and Nanjing from 2005 to 2008.Six mutants with stable high percentage of chalkiness (>80% vs. <20 in Nipponbare) in rice grains were selected. The stable high chalky ratio in these mutants suggested the traits are suitable for further study.2. Plants of mu1, mu2, mu5, mu6 are positive in hygromycin label test, whlie plants of mu3, mu4 are negative in hygromycin label test.3. Six mutants are all white belly rice and no visible difference in mutants and wild type stained by iodine. Relative to wild type, the content of fructose, sucrose and total soluble sugar increased in all six mutants, especially in mu2,mu5.4. According the enzyme activity compared with wild type, the six mutants can be divided into three groups: mu1 and mu2 have lower sucrose synthase activity in the whole grain filling, higher AGPase activity in the early grain filling and higher SSⅠand total soluble starch synthase activity in the late grain filling. mu3 and mu6 have lower SSⅠ, total soluble starch synthase, pullulanase and isoamylase activity in the early grain filling and higher isoamylase activity in the late grain filling. The third group including mu4 and mu5, which present higher sucrose synthase in the early and middle grain filling, lower total soluble starch synthase activity in the whole grain filling, lower isoamylase activity in the early grain filling and higher isoamylase activity in the late grain filling.