Yuka Fukuie1, Hana Shimoyama1,2, Toshikazu Morishita3,4, Daisuke Tsugama1,5, Kaien Fujino6. 1. Laboratory of Crop Physiology, Research Faculty of Agriculture, Hokkaido University, Kita 9 Nishi 9 Kita-ku, Sapporo-shi, Hokkaido, 060-8589, Japan. 2. Division of African Area Studies, Graduate School of Asian and African Area Studies, Kyoto University, 46 Yoshida-shimo-adachi-cho, Sakyo-ku, Kyoto-shi, Kyoto, 606-8304, Japan. 3. National Agriculture and Food Research Organization (NARO) Hokkaido Agricultural Research Center, Memuro Upland Farming Research Station, Shinsei, Memuro, Kasai, Hokkaido, 082-0081, Japan. 4. Radiation Breeding Division, Institute of Crop Science, NARO, 2425 Kamimurata, Hitachiomiya, Ibaraki, 319-2293, Japan. 5. Asian Natural Environmental Science Center, The University of Tokyo, 1-1-1 Midori-cho, Nishi-tokyo-shi, Tokyo, 188-0002, Japan. 6. Laboratory of Crop Physiology, Research Faculty of Agriculture, Hokkaido University, Kita 9 Nishi 9 Kita-ku, Sapporo-shi, Hokkaido, 060-8589, Japan. kaien@res.agr.hokudai.ac.jp.
Abstract
MAIN CONCLUSION: Tartary buckwheat rice-type cultivars, which allow easy dehulling, lacked periclinal cell divisions that proceed underneath the epidermis in the proximity of ovary midribs in non-rice-type cultivars. The easy dehulling in these cultivars was associated with a G→A substitution in an AGAMOUS ortholog. Ease of dehulling in Tartary buckwheat (Fagopyrum tataricum) can affect the quality of its products. Tartary buckwheat cultivars that allow easy dehulling are called rice-type cultivars. The rice and non-rice hull types are determined by a single gene, but this gene is unclear. Here, we show that cells underneath the epidermis in the proximity of ovary midribs undergo periclinal cell divisions in non-rice-type cultivars but do not in a rice-type cultivar. The cells that arose from the periclinal cell divisions later underwent lignification, which should increase mechanical strength of hulls. In RNA sequencing, a partial mRNA of an AGAMOUS ortholog in Tartary buckwheat (FtAG) was found to be absent in the rice-type cultivar. Cloning of this gene revealed that this is a 42-bp deletion due to a G→A substitution at a splice acceptor site in the FtAG genomic region. In F2 progeny derived from a cross between non-rice-type and rice-type cultivars, all the rice-type plants exhibited the homozygous A/A allele at this site, whereas all the Tartary-type plants exhibited either the homozygous G/G allele or the heterozygous A/G allele. These results suggest that FtAG is a candidate for the gene that determines ease of dehulling in Tartary buckwheat. The DNA marker that we developed to distinguish the FtAG alleles can be useful in breeding Tartary buckwheat cultivars.
MAIN CONCLUSION: Tartary buckwheat rice-type cultivars, which allow easy dehulling, lacked periclinal cell divisions that proceed underneath the epidermis in the proximity of ovary midribs in non-rice-type cultivars. The easy dehulling in these cultivars was associated with a G→A substitution in an AGAMOUS ortholog. Ease of dehulling in Tartary buckwheat (Fagopyrum tataricum) can affect the quality of its products. Tartary buckwheat cultivars that allow easy dehulling are called rice-type cultivars. The rice and non-rice hull types are determined by a single gene, but this gene is unclear. Here, we show that cells underneath the epidermis in the proximity of ovary midribs undergo periclinal cell divisions in non-rice-type cultivars but do not in a rice-type cultivar. The cells that arose from the periclinal cell divisions later underwent lignification, which should increase mechanical strength of hulls. In RNA sequencing, a partial mRNA of an AGAMOUS ortholog in Tartary buckwheat (FtAG) was found to be absent in the rice-type cultivar. Cloning of this gene revealed that this is a 42-bp deletion due to a G→A substitution at a splice acceptor site in the FtAG genomic region. In F2 progeny derived from a cross between non-rice-type and rice-type cultivars, all the rice-type plants exhibited the homozygous A/A allele at this site, whereas all the Tartary-type plants exhibited either the homozygous G/G allele or the heterozygous A/G allele. These results suggest that FtAG is a candidate for the gene that determines ease of dehulling in Tartary buckwheat. The DNA marker that we developed to distinguish the FtAG alleles can be useful in breeding Tartary buckwheat cultivars.