Polymorphism of DNA sequences of cryptochrome genes is not associated with the photoperiodic flowering of wild soybean a
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Polymorphism of DNA sequences of cryptochrome genes is not associated with the photoperiodic flowering of wild soybean along a latitudinal cline Nobuchika Ishibashi • Hiroaki Setoguchi
Received: 14 October 2010 / Accepted: 10 December 2011 / Published online: 15 January 2012 Ó The Botanical Society of Japan and Springer 2012
Abstract Both cultivated soybean and its wild relative Glycine soja exhibit strong photoperiodic sensitivity at different latitudes. Recent studies have demonstrated that the blue light-absorbing cryptochrome gene, CRY1a, is involved in the photoperiodic flowering of soybeans. However, no sequence variation was found in the cDNA among cultivars at different latitudinal clines. In the present study, we examined whether positive selection due to polymorphisms in the cryptochrome genes of G. soja occurs. Partial DNA sequences, mainly exons, of cryptochrome genes CRY1a-1d and CRY2a–2c were analyzed for 18 accessions in the Japanese archipelago. The neutral evolutionary pattern of the polymorphisms for all cryptochrome genes except for CRY1a was summarized using Tajima’s D test and low nucleotide diversity was shown for all genes. Although CRY1a did not show neutral evolution, balancing selection was recognized in the intron while not in the exon. No geographical pattern of polymorphisms was observed in the cryptochrome genes. These results reject the possibility of cryptochrome genes being involved in the photoperiodic flowering of wild soybeans along a latitudinal cline. Keywords Balancing selection Cryptochromes Glycine soja Neutral evolution Photoreceptors
Electronic supplementary material The online version of this article (doi:10.1007/s10265-011-0470-6) contains supplementary material, which is available to authorized users. N. Ishibashi H. Setoguchi (&) Graduate School of Human and Environmental Studies, Kyoto University, Yoshida-nihonmatsucho, Sakyo-ku, Kyoto 606-8501, Japan e-mail: [email protected]
Introduction Soybean [Glycine max (L.) Merr.], one of the most important crops in the world, was domesticated in China about 3,000–5,000 years ago from its progenitor Glycine soja Sieb. & Zucc. (Hymowitz 1970). Presently, wild soybean (G. soja) is widely distributed in East Asia, including China, southeastern Russia, Korea, Taiwan, and Japan. In the Japanese archipelago, it is distributed from the islands of Hokkaido to Kyushu, with the exception of the Ryukyu Islands. Photoperiod is one of the most important environment factors in flowering in response to changing seasons (Garner and Akkard 1920). Most soybean varieties exhibit strong photoperiodic sensitivity, an adaptation to a narrow latitudinal range. Therefore, various soybean cultivars have been grown in suitable latitudinal ranges globally. This photoperiodic sensitivity to latitudinal cline originated from the nature of the wild soybean. Both G. max and G. soja exhibit strong photoperiodic sensitivities at the latitude of each habitat or cultivar [local cultivars and G. soja in China: Zhang
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