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 (TALE) homeobox genes (four KNOTTED-like homeobox (KNOX) and three BEL1-like homeobox (BELL) genes) identified after next generation sequencing (NGS) and assembly of the sporophyte and gametophyte transcriptomes of the endangered fern species Vandenboschia speciosa. Among the four KNOX genes, two belonged to the KNOX1 class and the other two belonged to the KNOX2 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 V. speciosa lifecycle, as well as in the control of the transition between both phases. Vandenboschia speciosa VsKNAT3 (a KNOX2 class protein) as well as VsBELL4 and VsBELL10 proteins have higher expression levels during the sporophyte program. On the contrary, one V. speciosa KNOX1 protein (VsKNAT6) and one KNOX2 protein (VsKNAT4) seem important during the development of the gametophyte phase. TALE 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 (VsKNAT3, VsKNAT6, VsBELL4, and VsBELL6) 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 TALE homeobox genes in V. speciosa, and gives novel insights about the role of these genes in fern development.
Highlights
The phylogenetic position of ferns as the sister lineage of seed plants makes the study of developmental genes in these vascular plants highly useful, and necessary to open new insights on plant evolutionary developmental biology [1,2,3,4,5,6,7]
three amino acid loop extension (TALE) 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 (VsKNAT3, VsKNAT6, VsBELL4, and VsBELL6) are upregulated in a non-alternating population in which only independent gametophytes are found
We identified the specificity of the amplified products by sequencing the quantitative reverse transcription polymerase chain reaction (qRT-PCR) products
Summary
The phylogenetic position of ferns as the sister lineage of seed plants makes the study of developmental genes in these vascular plants highly useful, and necessary to open new insights on plant evolutionary developmental biology [1,2,3,4,5,6,7]. One out of seven populations of this species located in the south of the Iberian Peninsula shows only the gametophyte phase All these features make this species an attractive species for the analysis of different developmental and evolutionary topics, including the ones with important implications for conservation biology. In this context, it is highly interesting to unravel and understand the genetics behind the control of the alternation of the two fern lifecycle phases by characterizing and analyzing homeobox genes, an issue for which the analysis of gametophyte independent populations of V. speciosa might represent an important advance
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