Abstract
Key messageThe fasciclin-like arabinogalactan proteins organization into four groups is conserved and may be related to specific roles in developmental processes across angiosperms.Fasciclin-like arabinogalactan proteins (FLAs) are a subclass of arabinogalactan proteins (AGPs), which contain fasciclin-like domains in addition to typical AGP domains. FLAs are present across all embryophytes, and despite their low overall sequence similarity, conserved regions that define the fasciclin functional domain (FAS) have been identified, suggesting that the cell adhesion property is also conserved. FLAs in Arabidopsis have been organized into four subgroups according to the number and distribution of functional domains. Recent studies associated FLAs with cell wall-related processes where domain organization seemed to be related to functional roles. In Arabidopsis, FLAs containing a single FAS domain were found to be important for the integrity and elasticity of the plant cell wall matrix, and FLAs with two FAS domains and two AGP domains were found to be involved in maintaining proper cell expansion under salt stress conditions. The main purpose of the present work was to elucidate the expression pattern of selected FLA genes during embryo and seed development using RT-qPCR. AtFLA8 and AtFLA10, two Arabidopsis genes that stood out in previous microarray studies of embryo development, were further examined using promoter-driven gene reporter analyses. We also studied the expression of cork oak FLA genes and found that their expression partially parallels the expression patterns of the putative AtFLA orthologs. We propose that the functional organization of FLAs is conserved and may be related to fundamental aspects of embryogenesis and seed development across angiosperms. Phylogenetic studies were performed, and we show that the same basic four-subgroup organization described for Arabidopsis FLA gene classification is valid for most Arabidopsis FLA orthologs of several plant species, namely poplar, corn and cork oak.
Highlights
Angiosperms are the vastest group of land plants (Wikström et al 2001; Jiao et al 2011)
As part of our contribution to the study of Arabidopsis and cork oak sexual reproduction (Costa et al 2015; Lopes et al 2016), we describe in the present work the developmental expression pattern of different Fasciclin-like arabinogalactan proteins (FLAs) genes in four different species: Arabidopsis, poplar, corn and cork oak, concluding that the expression patterns of this class of arabinogalactan proteins (AGPs) is conserved across these species and is potentially important for embryogenesis and seed development
The putative FLA sequences from these distantly related species cluster into four groups following the classification proposed for Arabidopsis FLAs (Johnson et al 2003; Fig. 1B)
Summary
Angiosperms are the vastest group of land plants (Wikström et al 2001; Jiao et al 2011). One of the most important characteristics of the flowering plants is the production of seeds. Seeds are consumed by humans, incorporated into animal feed and transformed into high-value-added products (FAO 2016). Seed development is the aftermath of pollination. Pollen lands on the stigma producing a pollen tube that transports the two sperm cells into the embryo sac for double fertilization: one fertilizes the egg cell to form the embryo, while the other fuses with the central cell to form the endosperm. The embryo and endosperm develop in such an interconnected way that embryogenesis is normally considered in the context of seed development
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