NOTE EVIDENCE FOR TUBULAR MATING STRUCTURES INDUCED IN EACH MATING TYPE OF HETEROTHALLIC GONIUM PECTORALE (VOLVOCALES, CHLOROPHYTA) 1 Yuko Mogi Department of Biological Sciences, Graduate School of Science, University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-0033, Japan Takashi Hamaji Department of Botany, Laboratory of Plant Molecular Genetics, Kyoto University, Oiwake-cho, Kita-shirakawa, Sakyo-ku, Kyoto 606-8502, Japan Masahiro Suzuki Department of Biological Sciences, Graduate School of Science, University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-0033, Japan Patrick Ferris Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, Arizona 85721, USA Toshiyuki Mori Waseda Institute for Advanced Study (WIAS), Waseda University, 1-6-1 Nishiwaseda, Shinjuku-ku, Tokyo 169-8050, Japan Yukihiro Kabeya, Shin-ya Miyagishima Center for Frontier Research, National Institute of Genetics, 1111 Yata, Mishima, Shizuoka 411-8540, Japan and Hisayoshi Nozaki 2 Department of Biological Sciences, Graduate school of Science, University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-0033, Japan Gametes were induced separately in cultures of each mating type of the heterothallic, isogamous colonial volvocalean Gonium pectorale O. F. Mu ¨ll. to examine the tubular mating structure (TMS) of both mating types plus and minus (plus and minus), referred to as ‘‘bilateral mating papillae.’’ Addition of dibutyryl cyclic adenosine monophosphate (DcAMP or db-cAMP) and 3-isobutyl-1-methylxan- thine (IBMX) to approximately 3-week-old cultures of each mating type induced immediate release of naked gametes from the cell walls. Both plus and minus gametes formed a TMS in the anterior region of the protoplasts. Accumulation of actin was visualized by antibody staining in the TMS of both mating types as occurs in the TMS (fertiliza- tion tubule) of the plus gametes of the unicellular volvocalean Chlamydomonas reinhardtii P. A. Dang. Induction of naked gametes with a TMS in each mating type will be useful for future cell biological and evolutionary studies of the isogametes of colo- nial volvocalean algae. Key index words: bilateral mating papilla; Chloro- phyta; Gonium pectorale; isogamete; mating type; sexual reproduction; tubular mating structure; Volvocales Abbreviations: DcAMP (db-cAMP), dibutyryl cyclic adenosine monophosphate; IBMX, 3-isobutyl-1- methylxanthine; MID, minus dominance gene; minus , mating type minus; plus , mating type plus; RT-PCR, reverse transcription–polymerase chain reaction; TMS, tubular mating structure The colonial volvocalean algae are composed of both isogamous and anisogamous ⁄ oogamous species and form a recently derived monophyletic group (Nozaki et al. 2000, 2003, Herron et al. 2009). This group includes the multicellular, oogamous model species Volvox carteri (Kirk 1998, Ferris et al. 2010) and is closely related to the unicellular, isogamous model species C. reinhardtii (Harris et al. 2008). Thus, the colonial Volvocales represent a model lineage to study the evolutionary linkage between isogamy and oogamy ⁄ anisogamy. In C. reinhardtii, only one of the two conjugating isogametes forms a TMS called a ‘‘fertilization tubule’’ (Friedmann et al. 1968); this sex is desig- nated ‘‘mating type plus’’ (plus), and it lacks the minus dominance gene (MID) that determines 1 Received 25 August 2011. Accepted 18 October 2011. 2 Author for correspondence: e-mail nozaki@biol.s.u-tokyo.ac.jp. J. Phycol. 48, 670–674 (2012) Ó 2012 Phycological Society of America DOI: 10.1111/j.1529-8817.2012.01149.x 670