Identification of WOX Family Genes in Selaginella kraussiana for Studies on Stem Cells and Regeneration in Lycophytes

Abstract

Plant stem cells give rise to all tissues and organs and also serve as the source for plant regeneration. The organization of plant stem cells has undergone a progressive change from simple to complex during the evolution of vascular plants. Most studies on plant stem cells have focused on model angiosperms, the most recently diverged branch of vascular plants. However, our knowledge of stem cell function in other vascular plants is limited. Lycophytes and euphyllophytes (ferns, gymnosperms, and angiosperms) are two existing branches of vascular plants that separated more than 400 million years ago. Lycophytes retain many of the features of early vascular plants. Based on genome and transcriptome data, we identified WUSCHEL-RELATED HOMEOBOX (WOX) genes in Selaginella kraussiana, a model lycophyte that is convenient for in vitro culture and observations of organ formation and regeneration. WOX genes are key players controlling stem cells in plants. Our results showed that the S. kraussiana genome encodes at least eight members of the WOX family, which represent an early stage of WOX family evolution. Identification of WOX genes in S. kraussiana could be a useful tool for molecular studies on the function of stem cells in lycophytes.

Transcription Factors WOX11/12 Directly Activate WOX5/7 to Promote Root Primordia Initiation and Organogenesis

“…WOX11/12 are intermediate-clade WOX genes, while WOX5/7 are in the WUS clade (Supplemental Fig. S1A; Haecker et al, 2004;Sarkar et al, 2007;Mukherjee et al, 2009;Nardmann et al, 2009;van der Graaff et al, 2009;Zhao et al, 2009;Nardmann and Werr, 2013;Lian et al, 2014;Pi et al, 2015;Ge et al, 2016;Zeng et al, 2016). Therefore, we propose that the switch between the two clades of WOX genes represents the fate transition from root founder cells to root primordium cells in de novo root organogenesis.…”

A fern WUSCHEL-RELATED HOMEOBOX gene functions in both gametophyte and sporophyte generations

“…The progenitor of WOX genes existed in the last common ancestor of land plants and green algae and, through successive gene duplication and functional diversification, gave rise to the three clades of WOX genes [9, 12]. All land plants that have been examined, non-vascular and vascular alike, possess WOX genes of the ancient clade, while the intermediate clade only exists in vascular plants, and the modern clade is found in seed plants and ferns, but has not been found in lycophytes [13, 14]. Based on the presence of two subgroups of the intermediate clade in the lycophytes and sequence relatedness of only one subgroup to the modern clade WOX genes, it has been proposed that the intermediate subgroup shared a progenitor with the modern clade [11, 14].…”

“…All land plants that have been examined, non-vascular and vascular alike, possess WOX genes of the ancient clade, while the intermediate clade only exists in vascular plants, and the modern clade is found in seed plants and ferns, but has not been found in lycophytes [13, 14]. Based on the presence of two subgroups of the intermediate clade in the lycophytes and sequence relatedness of only one subgroup to the modern clade WOX genes, it has been proposed that the intermediate subgroup shared a progenitor with the modern clade [11, 14]. The modern clade, or the WUS clade, has experienced further expansion in seed plants as Picea abies possesses five and A. thaliana possesses eight WUS clade members [9, 15], compared to the single member found in the fern, Ceratopteris richardii [11].…”

Wound signaling: The missing link in plant regeneration

“…6,7 Many studies have tried to clarify the effects of wounding on regeneration by analysis of the genes downstream of wound signaling. [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] However, our knowledge about whether and how the above physical and chemical signals serve as wound signal (s) in plant regeneration is still limited.…”