TY - CONF

T1 - ORIGIN AND EVOLUTION OF APICAL MERISTEMS IN PLANTS

AU - Романова, Марина Андреевна

AU - Максимова, Анастасия

AU - Домашкина, Валентина Владимировна

AU - Войцеховская, Ольга Владимировна

N1 - Conference code: VII

PY - 2026/6/8

Y1 - 2026/6/8

N2 - A key feature of plant morphogenesis – the origin of new organs throughout life – is called apical, growth and is mediated by the apical meristems (AMs). Apical growth in bryophyte gametophytes (Anthocerotophyta, Marchantiophyta, Bryophyta) likely evolved from that in the gametophytes of algal ancestors, Charophyta. Whether apical growth in sporophytes resulted from the modification of gametophyte meristems or de novo is debatable.To access the origin and evolution of apical growth we analysed the structure and regulation of AM in gametophytes and sporophytes in all plant taxa. The presence of multiple initials and secondary plasmodesmata in the AM of gametophytes in Anthocerotophyta and Marchantiophyta and sporophytes in Lycopodiales and Isoetales suggests that post-cytokinetic plasmodesmata and simplex meristems arose in the common ancestor of land plants but were lost in gametophytes Bryophyta and sporophytes of Selaginellales and Polypodiopsida (Romanova et al., 2022).The key regulators of AM cells in angiosperms – C1KNOX – are sporophyte-specific. They regulate expression of zygotic genes in alga Chlamydomonas, diffuse cell proliferation in the embryo of Marchantiophyta, intercalary meristem in the sporophytes of Bryophyta. The shift of C1KNOX expression to the apical pole caused the emergence of AM in sporophytes (Romanova et al., 2023,2025).Homologues of the "organizer" of angiosperm AM – WUS – belong to T3 superclade of WOX and emerged in ferns, where regulated the apical growth in gametophytes and organogenesis in sporophytes. Functiong of AM regulation in sporophytes evolved only in WUS/WOX5 clade, that emerged in seed plants (Romanova et al., 2023).CLE/CLAVATA module emerged in the common ancestor of land plants and caused the transformation of the 2-D into 3-D thalli and branching in gametophytes of bryophytes. The role of regulation of the AM in sporophytes evolved in seed plants (Romanova et al., 2023).The switch between meristematic and organogenetic programs in angiosperms comes from antagonistic interaction between C1KNOX and "leaf regulators" (ARP, C3HDZ, YABBY, KANADI). Their homologues are found in bryophytes and likely arose in the common ancestor of land plants. However, neither in gametophytes of Bryophyta nor in sporophytes of non-seed plants they act antagonistic to the regulators of the AM, indicating that the organogenesis program may have resulted from modification of the shoot dichotomy program (Evkaikina et al., 2017, Romanova et al., 2021,2023).Overall presence of main angiosperm AM regulators in bryophyte gametophytes does not favor de novo emergence of AM in sporophytes of land plants.

AB - A key feature of plant morphogenesis – the origin of new organs throughout life – is called apical, growth and is mediated by the apical meristems (AMs). Apical growth in bryophyte gametophytes (Anthocerotophyta, Marchantiophyta, Bryophyta) likely evolved from that in the gametophytes of algal ancestors, Charophyta. Whether apical growth in sporophytes resulted from the modification of gametophyte meristems or de novo is debatable.To access the origin and evolution of apical growth we analysed the structure and regulation of AM in gametophytes and sporophytes in all plant taxa. The presence of multiple initials and secondary plasmodesmata in the AM of gametophytes in Anthocerotophyta and Marchantiophyta and sporophytes in Lycopodiales and Isoetales suggests that post-cytokinetic plasmodesmata and simplex meristems arose in the common ancestor of land plants but were lost in gametophytes Bryophyta and sporophytes of Selaginellales and Polypodiopsida (Romanova et al., 2022).The key regulators of AM cells in angiosperms – C1KNOX – are sporophyte-specific. They regulate expression of zygotic genes in alga Chlamydomonas, diffuse cell proliferation in the embryo of Marchantiophyta, intercalary meristem in the sporophytes of Bryophyta. The shift of C1KNOX expression to the apical pole caused the emergence of AM in sporophytes (Romanova et al., 2023,2025).Homologues of the "organizer" of angiosperm AM – WUS – belong to T3 superclade of WOX and emerged in ferns, where regulated the apical growth in gametophytes and organogenesis in sporophytes. Functiong of AM regulation in sporophytes evolved only in WUS/WOX5 clade, that emerged in seed plants (Romanova et al., 2023).CLE/CLAVATA module emerged in the common ancestor of land plants and caused the transformation of the 2-D into 3-D thalli and branching in gametophytes of bryophytes. The role of regulation of the AM in sporophytes evolved in seed plants (Romanova et al., 2023).The switch between meristematic and organogenetic programs in angiosperms comes from antagonistic interaction between C1KNOX and "leaf regulators" (ARP, C3HDZ, YABBY, KANADI). Their homologues are found in bryophytes and likely arose in the common ancestor of land plants. However, neither in gametophytes of Bryophyta nor in sporophytes of non-seed plants they act antagonistic to the regulators of the AM, indicating that the organogenesis program may have resulted from modification of the shoot dichotomy program (Evkaikina et al., 2017, Romanova et al., 2021,2023).Overall presence of main angiosperm AM regulators in bryophyte gametophytes does not favor de novo emergence of AM in sporophytes of land plants.

KW - SHOOT APICAL MERISTEM

KW - TRANSCRIPTION FACTOR

KW - EVOLUTION

M3 - Paper

SP - 121

EP - 121

Y2 - 8 June 2026 through 11 June 2026

ER -