Sang Yeop Sung

Analysis of the genetic relationship of gamma-irradiated in vitro mutants derived from standard-type chrysanthemum cv. Migok

In Korea, chrysanthemum is the second-most popular cutflower next to roses and can be divided into two main groups: spray and standard types according to their usage. The standard-type chrysanthemums are often used for condolence, and the important traits of this type include lack of branching and a long flowering period. This study was performed to compare the polymorphisms, genetic diversity, and genetic distances between the original variety and gamma-irradiated in vitro plants using amplified fragment length polymorphism (AFLP) markers. The in vitro explants derived from a standard-type flower, ‘Migok’, were gamma-irradiated at 0, 30, 50, 70, and 100 Gy, and the resulting genetic variations were more diverse in the in vitro populations than in the plants derived from conventional cuttings. We identified 83% (866 bands) of the polymorphisms using 12 primer combinations, and the highest polymorphism was detected using the M-CAT/E-ACC combination with a 30 Gy irradiation treatment. In addition, the genetic diversity and polymorphic information content value were the highest at 30 Gy irradiation of the in vitro population, whereas the genetic distance was the furthest between the 30 Gy-irradiated and other populations. Therefore, 30 Gy is the most effective dosage for inducing in vitro genetic variations in standard-type Migok.

Comparative gene expression analysis in a highly anthocyanin pigmented mutant of colorless chrysanthemum.

In this study, we investigated differentially expressed genes between the original chrysanthemum cultivar ‘Argus’ with white flower color and its gamma-ray irradiated mutant ‘ARTI-purple’ with purple flower color. The expression levels of anthocyanin biosynthetic genes were not associated with anthocyanin accumulations of Argus and ARTI-purple. Expressed sequence tags (ESTs) analysis was performed to identify a novel cDNAs encoding enzymes of specific plant metabolic pathways and the biological effects of gamma-ray mutation through alterations in expression in each flower. A total of 796 unigenes were isolated from chrysanthemum ray florets. These unigenes were functionally classified using gene ontologies and tentative pathway associations were established to 99 sequences in the Kyoto encyclopedia of genes and genomes. The expressions of the isolated ESTs were screened by cDNA dot blot hybridization. Seven differentially expressed genes were identified as being involved in carbohydrate and lipid metabolic pathways and five as transcription factor or signal transduction genes. Of particular note, decreased expression of CmMYB1 was identified at the ‘ARTI-purple’. The CmMYB1 shared high similarity with AtMYB4 and AtMYBL2 which is a negative regulator of anthocyanin and flavonol accumulation. Furthermore, two genes involved in lipid metabolism, enoyl-ACP reductase and [acyl-carrier-protein] S-malonyltransferase, were decreased in the ‘ARTI-purple’ flower. Our results suggest that the purple pigmentation of the ‘ARTI-purple’ is not just dependent on the expression of anthocyanin synthesis genes, and that the pigmentation may also affect other metabolic processing and the plant cell environment.

Genetic relationships among diverse spray- and standard-type chrysanthemum varieties and their derived radio-mutants determined using AFLPs

Gamma-ray irradiation is an important tool in ornamental plant breeding, particularly to induce flower-color variation. Standard-type chrysanthemum ‘Migok’ and spray-type ‘Argus’ have seven and four gamma-ray mutants, respectively, with novel flower colors. Genetic relationships among 26 chrysanthemum varieties or mutants were analyzed using amplified fragment length polymorphisms (AFLPs) with 20 fluorescently-labeled E+3/M+3 primer combinations (PCs). Clustering analysis was carried out using similarity coefficients and unweighted pair group method with arithmetic averages (UPGMA). The 20 PCs produced 2,837 bands, 95.6% of which were polymorphic. E-ACC/M-CAG had the most polymorphic bands (199) and high polymorphic information content, marker index, and resolving power values. Similarity coefficients ranged from 0.63 to 0.97 overall but were 0.73–0.83 in the 11 radio-mutants. The 26 varieties and radio-mutants were divided into four major UPGMA groups; the 11 radio-mutants formed two subgroups and 10 standard-type varieties or radio-mutants were closely clustered into another. The most promising mutant-specific marker candidates were PC E-ACG/M-CAG (47.5%) and E-ACA/M-CAT (44%) for the ‘Migok’ and ‘Argus’ families, respectively.