BACKGROUND: Land plants (embryophytes) are monophyletic and encompass four major clades: liverworts, mosses, hornworts and polysporangiophytes. The liverworts are resolved as the earliest divergent lineage and the mosses as sister to a crown clade formed by the hornworts and polysporangiophytes (lycophytes, monilophytes and seed plants). Alternative topologies resolving the hornworts as sister to mosses plus polysporangiophytes are less well supported. Sporophyte development in liverworts depends only on embryonic formative cell divisions. A transient basal meristem contributes part of the sporophyte in mosses. The sporophyte body in hornworts and polysporangiophytes develops predominantly by post-embryonic meristematic activity. SCOPE: This paper explores the origin of the sporophyte shoot in terms of changes in embryo organization. Pressure towards amplification of the sporangium-associated photosynthetic apparatus was a major driver of sporophyte evolution. Starting from a putative ancestral condition in which a transient basal meristem produced a sporangium-supporting seta, we postulate that in the hornwort-polysporangiophyte lineage the basal meristem acquired indeterminate meristematic activity and ectopically expressed the sporangium morphogenetic programme. The resulting sporophyte body plan remained substantially unaltered in hornworts, whereas in polysporangiophytes the persistent meristem shifted from a mid-embryo to a superficial position and was converted into an ancestral shoot apical meristem with the evolution of sequential vegetative and reproductive growth. CONCLUSIONS: The sporophyte shoot is interpreted as a sterilized sporangial axis interpolated between the embryo and the fertile sporangium. With reference to the putatively ancestral condition found in mosses, the sporophyte body plans in hornworts and polysporangiophytes are viewed as the product of opposite heterochronic events, i.e. an anticipation and a delay, respectively, in the development of the sporangium. In either case the result was a pedomorphic sporophyte permanently retaining juvenile characters.
BACKGROUND:Land plants (embryophytes) are monophyletic and encompass four major clades: liverworts, mosses, hornworts and polysporangiophytes. The liverworts are resolved as the earliest divergent lineage and the mosses as sister to a crown clade formed by the hornworts and polysporangiophytes (lycophytes, monilophytes and seed plants). Alternative topologies resolving the hornworts as sister to mosses plus polysporangiophytes are less well supported. Sporophyte development in liverworts depends only on embryonic formative cell divisions. A transient basal meristem contributes part of the sporophyte in mosses. The sporophyte body in hornworts and polysporangiophytes develops predominantly by post-embryonic meristematic activity. SCOPE: This paper explores the origin of the sporophyte shoot in terms of changes in embryo organization. Pressure towards amplification of the sporangium-associated photosynthetic apparatus was a major driver of sporophyte evolution. Starting from a putative ancestral condition in which a transient basal meristem produced a sporangium-supporting seta, we postulate that in the hornwort-polysporangiophyte lineage the basal meristem acquired indeterminate meristematic activity and ectopically expressed the sporangium morphogenetic programme. The resulting sporophyte body plan remained substantially unaltered in hornworts, whereas in polysporangiophytes the persistent meristem shifted from a mid-embryo to a superficial position and was converted into an ancestral shoot apical meristem with the evolution of sequential vegetative and reproductive growth. CONCLUSIONS: The sporophyte shoot is interpreted as a sterilized sporangial axis interpolated between the embryo and the fertile sporangium. With reference to the putatively ancestral condition found in mosses, the sporophyte body plans in hornworts and polysporangiophytes are viewed as the product of opposite heterochronic events, i.e. an anticipation and a delay, respectively, in the development of the sporangium. In either case the result was a pedomorphic sporophyte permanently retaining juvenile characters.
Authors: John F Emery; Sandra K Floyd; John Alvarez; Yuval Eshed; Nathaniel P Hawker; Anat Izhaki; Stuart F Baum; John L Bowman Journal: Curr Biol Date: 2003-10-14 Impact factor: 10.834
Authors: Elizabeth M Ruszala; David J Beerling; Peter J Franks; Caspar Chater; Stuart A Casson; Julie E Gray; Alistair M Hetherington Journal: Curr Biol Date: 2011-06-09 Impact factor: 10.834
Authors: Karen S Renzaglia; Juan Carlos Villarreal; Bryan T Piatkowski; Jessica R Lucas; Amelia Merced Journal: Plant Physiol Date: 2017-04-18 Impact factor: 8.340
Authors: Fay-Wei Li; Tomoaki Nishiyama; Manuel Waller; Eftychios Frangedakis; Jean Keller; Zheng Li; Noe Fernandez-Pozo; Michael S Barker; Tom Bennett; Miguel A Blázquez; Shifeng Cheng; Andrew C Cuming; Jan de Vries; Sophie de Vries; Pierre-Marc Delaux; Issa S Diop; C Jill Harrison; Duncan Hauser; Jorge Hernández-García; Alexander Kirbis; John C Meeks; Isabel Monte; Sumanth K Mutte; Anna Neubauer; Dietmar Quandt; Tanner Robison; Masaki Shimamura; Stefan A Rensing; Juan Carlos Villarreal; Dolf Weijers; Susann Wicke; Gane K-S Wong; Keiko Sakakibara; Péter Szövényi Journal: Nat Plants Date: 2020-03-13 Impact factor: 15.793