Development and Cell Cycle Activity of the Root Apical Meristem in the Fern Ceratopteris richardii.

Ikram Blilou,Luis Herrera-Estrella,Alejandra Vasco,Alejandro Aragón-Raygoza,Alfredo Cruz-Ramírez

doi:10.3390/genes11121455

Abstract

Ferns are a representative clade in plant evolution although underestimated in the genomic era. Ceratopteris richardii is an emergent model for developmental processes in ferns, yet a complete scheme of the different growth stages is necessary. Here, we present a developmental analysis, at the tissue and cellular levels, of the first shoot-borne root of Ceratopteris. We followed early stages and emergence of the root meristem in sporelings. While assessing root growth, the first shoot-borne root ceases its elongation between the emergence of the fifth and sixth roots, suggesting Ceratopteris roots follow a determinate developmental program. We report cell division frequencies in the stem cell niche after detecting labeled nuclei in the root apical cell (RAC) and derivatives after 8 h of exposure. These results demonstrate the RAC has a continuous mitotic activity during root development. Detection of cell cycle activity in the RAC at early times suggests this cell acts as a non-quiescent organizing center. Overall, our results provide a framework to study root function and development in ferns and to better understand the evolutionary history of this organ.

Highlights

Exploring the diversity of plant lineages using evo-devo approaches provides insights of how different organs and certain innovations that integrate the sporophyte plant body emerged during the evolution of embryophytes [1] (Figure 1A)
We explored the early stages of Ceratopteris sporophyte to understand the embryo development and to track the emergence of the first root
Male gametophytes are filled with antheridia and circularized sperms are observed inside them (Figure 2A and Figure S1A)

Summary

Introduction

Exploring the diversity of plant lineages using evo-devo approaches provides insights of how different organs and certain innovations that integrate the sporophyte plant body emerged during the evolution of embryophytes [1] (Figure 1A). Several studies suggest that convergent evolutionary events took place in both extant tracheophyte lineages: lycophytes and euphyllophytes (ferns and seed plants; Figure 1A, blue circles). Root evolution in lycophytes is considered the first appearance of this organ in vascular plants, followed by a second evolutionary event which likely occurred in the ancestor of euphyllophytes [6] (Figure 1A). Ceratopteris richardii (Ceratopteris) is a subtropical fern in the Pteridaceae family, which has been considered “the Arabidopsis of the fern world” This fern presents certain advantages: easiness to culture in laboratory; short life cycle; genetic transformation techniques; and a draft genome sequence [8,9,10,11,12,13]. An accurate and complete characterization of its ontogenesis is necessary to pursue further research with this organism

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