Identification and Characterization of TALE Homeobox Genes in the Endangered Fern Vandenboschia speciosa

Abstract

We report and discuss the results of a quantitative reverse transcription polymerase chain reaction (qRT-PCR) analysis of the expression patterns of seven three amino acid loop extension (<i>TALE</i>) homeobox genes (four <i>KNOTTED-like homeobox</i> (<i>KNOX</i>) and three <i>BEL1-like homeobox</i> (<i>BELL</i>) genes) identified after next generation sequencing (NGS) and assembly of the sporophyte and gametophyte transcriptomes of the endangered fern species <i>Vandenboschia speciosa</i>. Among the four <i>KNOX</i> genes, two belonged to the <i>KNOX1</i> class and the other two belonged to the <i>KNOX2</i> class. Analysis of the deduced amino acid sequences supported the typical domain structure of both types of TALE proteins, and the homology to TALE proteins of mosses, lycophytes, and seed plant species. The expression analyses demonstrate that these homeodomain proteins appear to have a key role in the establishment and development of the gametophyte and sporophyte phases of <i>V. speciosa</i> lifecycle, as well as in the control of the transition between both phases. <i>Vandenboschia speciosa</i> VsKNAT3 (a KNOX2 class protein) as well as VsBELL4 and VsBELL10 proteins have higher expression levels during the sporophyte program. On the contrary, one <i>V. speciosa KNOX1</i> protein (VsKNAT6) and one KNOX2 protein (VsKNAT4) seem important during the development of the gametophyte phase. <i>TALE</i> homeobox genes might be among the key regulators in the gametophyte-to-sporophyte developmental transition in regular populations that show alternation of generations, since some of the genes analyzed here (<i>VsKNAT3</i>, <i>VsKNAT6</i>, <i>VsBELL4</i>, and <i>VsBELL6</i>) are upregulated in a non-alternating population in which only independent gametophytes are found (they grow by vegetative reproduction outside of the range of sporophyte distribution). Thus, these four genes might trigger the vegetative propagation of the gametophyte and the repression of the sexual development in populations composed of independent gametophytes. This study represents a comprehensive identification and characterization of <i>TALE</i> homeobox genes in <i>V. speciosa</i>, and gives novel insights about the role of these genes in fern development.