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内容記述 |
The ANS gene encoding anthocyanidin synthase catalyzes 2-oxoglutarate-dependent oxidation of leucoanthocyanidins to yield anthocyanidins in the biosynthesis pathway of anthocyanin pigments. The ANS gene was first isolated from maize and snapdragon, mutants of which are deficient in pigmentation: the mutations in the A2 (ANS) gene caused by insertion of transposons in maize control coloration in the aleurone layer of the kernel and a large deletion mutation including the candi (ANS) gene in snapdragon confers completely acyanic flowers. Although several ANS cDNAs were isolated from various tissues of plants including flowers of petunia and torenia subsequently, no insertion mutations in the ANS genes affecting flower pigmentation have been reported.<br /> The wild-type Japanese morning glory (Ipomoea nil or Pharbitis nil) bears blue flowers, and a number of mutants related to the color and shape of its flowers have been isolated since the 17th century in Japan. All of the mutants available are spontaneous mutants and most of them were isolated more than 60 years ago. Several lines of evidence indicate that an En/Spm-related transposable element Tpn1 and its relatives are common spontaneous mutagens in the plant. Here he describe that three spontaneous mutants displaying stable white flowers and a newly isolated mutable line exhibiting white flowers with red sectors are caused by insertion of Tpn1-related transposable elements into the ANS gene of the Japanese morning glory.<br /> Three stable white flower mutants, r-3, Carol White and Waisei-asagao-hakushoku, were found to carry an identical insertion of the 6.6-kb Tpn1 -related transposable element, Tpn8, at the promoter of the ANS gene. No excision of Tpn8 could be detected by PCR analysis, indicating that the insertion mutation appeared to be quite stable. While Carol White and Waisei-asagao- hakushoku showed stable null mutant phenotype, r-3 displayed a leaky phenotype since pale red pigmentation was observed when its flowers were wilting. In consistent with this notion, reduced but significant amount of the ANS mRNA accumulation was detected by RT-PCR analysis in the floral organs of the r-3 mutant.<br /> Another newly isolated mutable line, Shibori-chidori, that exhibits white flowers with red spots and sectors, was isolated about three years ago from a red flower cultivar Beni-chidori. Molecular analysis showed that the 6.4-kb Tpn1-variant, Tpn9, inserted into the unique intron of the ANS gene. The flower variegation is due to the somatic excision of Tpn9 from the ANS gene. Tpn9 and Tpn1 are 6422 bp and 6412 bp, respectively, and their size differences are mainly due to the lengths of a particular A-stretch within the elements. Compared with Tpn1, Tpn9 contains 13 single nucleotide alterations.<br /> To their knowledge, the mutants described here are the first ANS insertion mutants deficient in flower pigmentation. Since the mutable line Shibori-chidori was isolated recently, Tpn1-related elements still act as an active spontaneous mutagen that would generate new interesting traits in the Japanese morning glory. |
要旨・審査要旨 / Abstract, Screening Result (231.4 kB)
