Characterization And Gene Mapping Of An Albino Green-Revertible Mutant G₉ In Rice

Chloroplast development and chlorophyll metabolism is crucial to all plants in relation to photosynthesis. Also, mutations of them usually result in the differences of leaf color. A great deal chlorophyll-and chloroplast-associated mutations that affect leaf coloration and/or seedling viability now have been identified in rice. Albino green-revertible mutant is a special one among these mutants and its chlorotic leaves can resort to green with the development and growth of plant. This kind of mutant exhibit albino phenotype during the early growing stage owing to chlorophyll deficiency, but can produce chlorophyll to display green phenotype at the late growth-stage. Green revertible albino mutant expresses its mutant phenotype in growth stage-dependent manner. Such albino green-revertible mutants not only can be applied as leaf marker into thermo-sensitive genic male-sterile lines (TPGMS) and cytoplasmic male sterility (CMS) along with corresponding maintainer liners hybrid rice production, but also provide some theoretical basis and scientific knowledge for the chloroplast development in plants and functional genomics of photosynthesis.In this study, we focus on a new growth stage-dependent albino green-revertible rice mutant G9. The phenotype trait, pigment content, inheritance of the mutant, SSR haplotype between the mutant and its wild-type Guangzhan63S, as well as comparative analysis on F4 agronomy traits of G9/AM6 were investigated. Furthermore, the mutant gene was also mapped with SSRs and InDels markers.1. Phenotypic characterization of G9 mutantThe phenotypic expressivity of green-revertible albino in G9 was insensitive to temperature. Under paddy field conditions, G9 plants exhibited an abnormal albino phenotype up to the L4 stage, but then generated green leaves after the 4th leaf blade fully emerged from the sheath and the first three chlorotic leaves gradually reverted to green from the leaf vain toward the edge. Both the 4th leaf and the following leaves appeared normal green.2. The Chl contents of G9 mutantThe contents of Chla, Chlb at the L2 stage of G9 mutant were 0.24%,0.40% compared to those in Guangzhan63S. Although the Chla, Chlb concentrations at the L4 stage were still lower, the percentage of the two chlorophyll in G9 to its wild-type increased to 22.87%,42.66%, respectively. At the L6 stage, the Chla, Chlb concentrations of G9 were 97.34%,90.47%compared to those in Guangzhan63S. The leaf color of G9 mutant plants had consistent dynamic changes with the concentration of chlorophyll (CHL). These results demonstrated that the conformations of chlorophylls were delayed in G9.3. Genetic characterization of the G9 mutationThe F3 plants from G9XAM6 were planted and the leaf color segregation populations were analysed.The results indicated that separation ratio fitted for 3:1. Thus, the G9 mutant locus was controlled by a single nucleic recessive gene.4. The mapping of the mutated geneRM202 and RM287 were selected and used for analysis of 30 F2 mutant type individuals. The segregation of the G9 homozygote, heterozygote, and AM6 homozygote derived from the cross G9×AM6 were 10:19:1 and 21:9:0, respectively. This result implied that this mutated gene located between the SSR markers of RM202 and RM287 on chromosome 11. Moreover,63 more SSR loci and 36 InDels scattered between RM202 and RM287 on chromosome 11 as well as a total 859 mutant type F2 plants of G9/AM6 were used for mapping of the mutated gene. It could concluded that the clbGZ locus was in the region delimited by the InDels marker IDJ6 (0.16cM) and IDJ12 (0.25cM) with the physical distance of 1.34 Mb.5. Characterization of isogenic lines between G9 and its wild type144 SSR markers scattered on whole chromosomes in rice were used to determine the polymorphisms between G9 and its wild type. Among 110 pairs of SSR markers which amplified PCR products,109 SSR markers appeared no polymorphism between G9 and its wild-type except only one SSR-RM202 showed difference. The results showed that G9 mutant and Guzhang63S had a consistent single-genome and were highly isogenic lines.6. Effects of the mutated gene on the agronomic traits of F4 populationComparative analysis on F4 agronomy traits of G9/AM6 indicated that the mutated gene significantly decreased the total root number, the white root number, the length of the longest root and the plant height at the seedling stage, and the tillering ability, plant height, grain number per panicle, grain setting ratio,1000 grain weight as well as yield per plant at maturity, but didn't affect the effective tillers per plants.