Abstract
Radiation randomly induces chromosomal mutations in plants. However, it was recently found that the frequency of flower-color mutants could be specifically increased by upregulating anthocyanin pathway gene expression before radiation treatments. The mechanisms of chlorophyll biosynthesis and degradation are active areas of plant study because chlorophyll metabolism is closely connected to photosynthesis. In this study, we determined the dark/light treatment conditions that resulted in upregulation of the expression levels of six chlorophyll pathway genes, uroporphyrinogen III synthase (HEMD), uroporphyrinogen III decarboxylase (HEME2), NADPH-protochlorophyllide oxidoreductase (POR) A (PORA), chlorophyll synthase (CHLG), chlorophyllase (CLH2), and red chlorophyll catabolite reductase (RCCR), and measured their effects on the γ-irradiation-induced frequencies of leaf-color mutants in two Cymbidium cultivars. To degrade chlorophyll in rhizomes, 60–75 days of dark treatment were required. To upregulate the expressions of chlorophyll pathway genes, 10 days of light treatment appeared to be optimal. Dark/light treatments followed by γ-irradiation increased chlorophyll-related leaf mutants by 1.4- to 2.0-fold compared with γ-ray treatment alone. Dark/light treatments combined with γ-irradiation increased the frequency of leaf-color mutants in Cymbidium, which supports the wider implementation of a plant breeding methodology that increases the mutation frequency of a target trait by controlling the expression of target trait-related genes.
Highlights
IntroductionPhysical mutagens, such as X-rays [1,2,3], γ-rays [4,5,6], and ion particles [1,3,7,8,9], and chemical mutagens, such as ethyl methanesulfonate [1,3,10,11,12] and N-nitroso-N-methylurea [13,14,15], have been widely used to induce mutations in various plants
Takata et al [32] reported that the ratio of DNA double-strand breaks to γ-irradiation was higher in decondensed chromatin than in condensed chromatin, and Venkatesh et al [33] verified that sensitivity to γ-irradiation, in terms of DNA double-strand breaks, was higher in euchromatin than heterochromatin regions
Kim et al [37] demonstrated that sucrose and methyl jasmonate treatments increase the frequency of flower-color mutants induced by γ-irradiation in chrysanthemum, which confirms the upregulated expressions of several anthocyanin pathway genes
Summary
Physical mutagens, such as X-rays [1,2,3], γ-rays [4,5,6], and ion particles [1,3,7,8,9], and chemical mutagens, such as ethyl methanesulfonate [1,3,10,11,12] and N-nitroso-N-methylurea [13,14,15], have been widely used to induce mutations in various plants. Hase et al [34] suggested that radiation could increase the mutation frequency for flower color when the genes involved in flower-color synthesis are highly expressed. The effect of sucrose treatment on the expression of anthocyanin pathway genes, an important mechanism for altering flower color [35], has been demonstrated in Arabidopsis [36]. A sucrose treatment followed by a radiation treatment increases the frequencies of flower-color mutants in chrysanthemum and petunia, no anthocyanin pathway gene expression levels were measured [28,34]. Kim et al [37] demonstrated that sucrose and methyl jasmonate treatments increase the frequency of flower-color mutants induced by γ-irradiation in chrysanthemum, which confirms the upregulated expressions of several anthocyanin pathway genes
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