Abstract
The adaptation of plants to land required multiple morphological innovations. Among these include a variety of lateral organs that are initiated from apical meristems, in which the mantainance of undifferentiated stem cells is regulated by the homeodomain WUSCHEL-RELATED (WOX) transcription factors. Expansion of the WOX gene family has been associated with whole genome duplication (WGD) events and postulated to have been pivotal to the evolution of morphological complexity in land plants. Previous studies have classified the WOX gene family into three superclades (e.g., the ancient clade, the intermediate clade, and the modern clade). In order to improve our understanding of the evolution of the WOX gene family, we surveyed the WOX gene sequences from 38 genomes and 440 transcriptomes spanning the Viridiplantae and Rhodophyta. The WOX phylogeny inferred from 1039 WOX proteins drawn from 267 species with improved support along the backbone of the phylogeny suggests that the plant-specific WOX family contains three ancient superclades, which we term Type 1 (T1WOX, the WOX10/13/14 clade), Type 2 (T2WOX, the WOX8/9 and WOX11/12 clades), and Type 3 (T3WOX, the WUS, WOX1/6, WOX2, WOX3, WOX4 and WOX5/7 clades). Divergence of the T1WOX and T2WOX superclades may predate the diversification of vascular plants. Synteny analysis suggests contribution of WGD to expansion of the WOX family. Promoter analysis finds that the capacity of the WOX genes to be regulated by the auxin and cytokinin signaling pathways may be deeply conserved in the Viridiplantae. This study improves our phylogenetic context for elucidating functional evolution of the WOX gene family, which has likely contributed to the morphological complexity of land plants.
Highlights
The radiation of plants in their quest for land was accompanied by morphological innovations, such as 3D growth, roots, leaves, and flowers [1,2,3,4]
WOX5 expression in the quiescent center (QC) of root [23] is regulated by the protein complexes of (1) the double APETALA2 (AP2)-domain transcription factors PLETHORAs (PLTs) [24,25,26], (2) the GRAS family transcription factor SCARECROW (SCR)[27, 28], and (3) the TEOSINTE-BRANCHED CYCLOIDEA PCNA (TCP) transcription factors [29, 30], which bind to the PLTbinding site in the WOX5 promoter [31]
AUX/ IAA family members are absent from green algae [122] and AUXIN RESPONSE FACTOR (ARF) genes are not found in chlorophytes [121], our result suggests that the capability of WUSCHEL-RELATED HOMEMOBOX (WOX) genes to be regulated by auxin signaling pathway was established early in Viridiplantae, most components of the pathway did not evolve until the emergence of the land plants [121,122,123]
Summary
The radiation of plants in their quest for land was accompanied by morphological innovations, such as 3D growth, roots, leaves, and flowers [1,2,3,4]. WUS promotes stem cell proliferation in floral meristems, and helps activate the Type 2 MADS-box gene AGAMOUS (AG), which specifies reproductive floral organ identity and determinate growth of floral meristems, in collaboration with another transcription factor, LEAFY (LFY) [16,17,18,19]. Another WOX gene, WOX5, maintains the stem cell niche in the root apical meristem (RAM) [12, 20,21,22]. Besides WUS and WOX5, the other 13 members of the WOX gene family in Arabidopsis (Arabidopsis thaliana), except WOX10, have been funcitonally characterized to regulate meristem development in embryos, as well as vegetative and reproductive organs (Table 1)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
