植物の永続的な成長を支える分子機構を解明～成長点の司令塔を担う転写因子が鍵～

2025-12-26

2025-12-25 東京理科大学

東京理科大学、京都大学、東北大学、帝京大学などの研究チームは、コケ植物ゼニゴケを用いて、植物が一生にわたり成長し続ける「無限成長」を可能にする分子機構を解明した。成長点の幹細胞領域で高発現する転写因子MpARF2は、植物ホルモン・オーキシンへの応答を抑制しつつ、オーキシン生合成を促進するという二重の役割を担っていた。幹細胞で作られたオーキシンは周辺領域へ輸送され、器官形成を促す一方、幹細胞自身はその影響を受けない。つまり幹細胞領域は、周囲の分化を制御する「司令塔(オーガナイザー)」として機能しており、MpARF2がその中核因子であることが示された。本成果は植物の発生原理と進化理解を深め、将来的な作物改良や成長制御技術への応用が期待される。研究成果はCurrent Biologyに掲載された。

図1　ゼニゴケの野生型株とMpARF2遺伝子を破壊したMparf2^ge株

<関連情報>

Bクラスのオーキシン応答因子MpARF2は自由生活植物配偶体の分裂組織の組織化に必須である The B-class auxin response factor MpARF2 is essential for meristem organization in free-living plant gametophytes

Eduardo Flores-Sandoval ∙ Hidemasa Suzuki ∙ Jessica A. Lazner ∙ … ∙ Takayuki Kohchi ∙ Ryuichi Nishihama ∙ John L. Bowman
Current Biology Published:December 5, 2025
DOI:https://doi.org/10.1016/j.cub.2025.11.015

Highlights

The auxin response factor MpARF2 determines totipotency in Marchantia
MpARF2 promotes stem cell identity by creating a low-auxin-response environment
A- and B-ARFs competitively control auxin biosynthesis to form a meristem organizer
Meristematic auxin is actively exported by MpPIN1 to promote distal organogenesis

Summary

Land plants (embryophytes) are multicellular eukaryotes with a remarkable capacity to grow continuously during their life span. They achieve this by maintaining a reservoir of pluripotent stem cells in their meristems. In embryophytes, including both bryophytes and tracheophytes, the haploid gametophytic generation is inferred to be ancestrally free living. Gametophyte meristems are sites of auxin biosynthesis, but auxin promotes differentiation, and conversely, a lack of auxin results in the loss of differentiation. We report that in the liverwort Marchantia polymorpha, pluripotent stem cells are protected from auxin-mediated differentiation by the single B-class auxin response factor (MpARF2), an embryophyte-specific gene that antagonizes auxin responses. We describe the critical role of MpARF2 in meristem establishment and maintenance using reporter lines, loss- and gain-of-function alleles, and gene-interaction experiments. Mparf2 knockdown and knockout alleles, respectively, fail to maintain and form a functional meristem across developmental transitions, while overexpression of MpARF2 is sufficient to create additional meristems in dormant gemmae. Despite being an auxin-signaling antagonist, MpARF2 positively regulates auxin production by activating a YUCCA (MpYUC2) auxin biosynthetic enzyme in stem cells. Conversely, auxin responses mediated by the single A-ARF (MpARF1) antagonize both auxin production and MpARF2 expression in differentiating neighbor cells, creating a multicellular incoherent feedforward loop that limits meristem size. We propose that MpARF2 and auxin form a meristem organizer—modulating auxin insensitivity at the site of auxin production while providing signaling information to surrounding differentiating cells—and that this organizer was critical for the emergence of indeterminate growth in the ancestral embryophyte.