Abstract
During evolution of land plants, the first colonizing species presented leafy-dominant gametophytes, found in non-vascular plants (bryophytes). Today, bryophytes include liverworts, mosses, and hornworts. In the first seedless vascular plants (lycophytes), the sporophytic stage of life started to be predominant. In the seed producing plants, gymnosperms and angiosperms , the gametophytic stage is restricted to reproduction. In mosses and ferns, the haploid spores germinate and form a protonema, which develops into a leafy gametophyte producing rhizoids for anchorage, water and nutrient uptakes. The basal gymnosperms (cycads and Ginkgo) reproduce by zooidogamy. Their pollen grains develop a multi-branched pollen tube that penetrates the nucellus and releases flagellated sperm cells that swim to the egg cell. The pollen grain of other gymnosperms (conifers and gnetophytes) as well as angiosperms germinates and produces a pollen tube that directly delivers the sperm cells to the ovule (siphonogamy). These different gametophytes, which are short or long-lived structures, share a common tip-growing mode of cell expansion. Tip-growth requires a massive cell wall deposition to promote cell elongation, but also a tight spatial and temporal control of the cell wall remodeling in order to modulate the mechanical properties of the cell wall. The growth rate of these cells is very variable depending on the structure and the species, ranging from very slow (protonemata, rhizoids, and some gymnosperm pollen tubes), to a slow to fast-growth in other gymnosperms and angiosperms. In addition, the structural diversity of the female counterparts in angiosperms (dry, semi-dry vs wet stigmas, short vs long, solid vs hollow styles) will impact the speed and efficiency of sperm delivery. As the evolution and diversity of the cell wall polysaccharides accompanied the diversification of cell wall structural proteins and remodeling enzymes, this review focuses on our current knowledge on the biochemistry, the distribution and remodeling of the main cell wall polymers (including cellulose, hemicelluloses, pectins, callose, arabinogalactan-proteins and extensins), during the tip-expansion of gametophytes from bryophytes, pteridophytes (lycophytes and monilophytes), gymnosperms and the monocot and eudicot angiosperms.
Highlights
The early non-vascular plants that successfully colonized land are thought to have been similar to extant bryophytes
This review highlights our current knowledge on the composition, distribution, and functional aspects of biosynthesis and remodeling of the main cell wall polymers including pectins, hemicelluloses, callose, cellulose, arabinogalactanproteins and extensins during the tip-expansion of gametophyte cells in bryophytes, pteridophytes, gymnosperms and the monocot and eudicot angiosperms
These external signals originate from the atmosphere, the soil, water and biotic interactions for protonemata and rhizoids, or from female tissues for pollen grains and pollen tubes
Summary
The early non-vascular plants that successfully colonized land are thought to have been similar to extant bryophytes. Honkanen et al (2016) demonstrated that several genes involved in rhizoid formation and growth in M. polymorpha were involved in root hairs as Menand et al (2007) mentioned on P. patens rhizoids This reveals that the mechanisms for constructing the tip-growing cells with absorption and anchorage functions were conserved among land plants and were active in the earliest ones (Jones and Dolan, 2012). This review highlights our current knowledge on the composition, distribution, and functional aspects of biosynthesis and remodeling of the main cell wall polymers including pectins, hemicelluloses, callose, cellulose, arabinogalactanproteins and extensins during the tip-expansion of gametophyte cells (protonemata, rhizoids and pollen tubes) in bryophytes, pteridophytes (lycophytes and monilophytes), gymnosperms and the monocot and eudicot angiosperms
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