Cheon Kyeong-Seong, Nakatsuka Akira, Tasaki Keisuke, Kobayashi Nobuo
Faculty of Life and Environmental Science, Shimane University, Matsue, Japan.
Genomics Division, National Institute of Agricultural Sciences, Rural Development Administration, Jeonju, South Korea.
Front Plant Sci. 2018 Jan 9;8:2239. doi: 10.3389/fpls.2017.02239. eCollection 2017.
Floral shape in higher plants typically requires genetic regulation through MADS transcription factors. In Japan, hundreds of azalea cultivars including flower shape mutations have been selected from the diversity of endogenous species and natural hybrids since the early 17th century, the Edo era (1603-1867). The long-lasting trait, known as "Misome-shō" in Japanese, has been identified in several species and cultivar groups of evergreen azaleas ( L.) from three hundred years ago in Japan. However, the natural mutation conferring the long-lasting trait in azalea remains unknown. Here, we showed MADS-box gene mutations in long-lasting flowers, 'Nikkō-misome,' 'Kochō-zoroi,' 'Chōjyu-hō,' and × 'Amagi-beni-chōjyu.' All of the long-lasting flowers exhibited small-sized corollas with stomata during long blooming. In the long-lasting flowers, transcript of the homolog was reduced, and an LTR-retrotransposon was independently inserted into exons 1, 2, and 7 or an unknown sequence in exon 1 in gDNA of each cultivar. This insertion apparently abolished the normal mRNA sequence of the homolog in long-lasting flowers. Also, long-lasting flowers were shown from F2 hybrids that had homozygous alleles. Therefore, we concluded that the loss of function of the homolog through a transposable element insertion may confer a stable long-lasting mutation in evergreen azaleas.
高等植物的花型通常需要通过MADS转录因子进行基因调控。自17世纪初江户时代（1603 - 1867年）以来，日本从本地物种和天然杂种的多样性中选育出了数百个包括花型突变在内的杜鹃花品种。在日本，一种名为“御装祥”的持久性状在300年前的几个常绿杜鹃（Rhododendron）物种和品种群中就已被发现。然而，赋予杜鹃持久性状的自然突变仍不清楚。在此，我们展示了“日光御装”“蝶装”“长寿法”和杂交品种“天城红长寿”等持久花中的MADS盒基因突变。所有持久花都表现出在长时间开花期间带有气孔的小型花冠。在持久花中，RcMADS homolog的转录本减少，并且一个LTR反转录转座子独立插入到每个品种gDNA的外显子1、2和7或外显子1中的一个未知序列中。这种插入显然消除了持久花中RcMADS homolog的正常mRNA序列。此外，F2杂种中具有纯合RcMADS等位基因的植株也表现出持久花。因此，我们得出结论，通过转座元件插入导致RcMADS homolog功能丧失可能赋予常绿杜鹃稳定的持久突变。
