Arabidopsis Tetraspanins Are Confined to Discrete Expression Domains and Cell Types in Reproductive Tissues and Form Homo- and Heterodimers When Expressed in Yeast      

Abstract

(L.C.B., P.Q., M.B., S.M.)Tetraspanins are evolutionary conserved transmembrane proteins present in all multicellular organisms. In animals, they are known to act as central organizers of membrane complexes and thought to facilitate diverse biological processes, such as cell proliferation, movement, adhesion, and fusion. The genome of Arabidopsis (Arabidopsis thaliana) encodes 17 members of the tetraspanin family; however, little is known about their functions in plant development. Here, we analyzed their phylogeny, protein topology, and domain structure and surveyed their expression and localization patterns in reproductive tissues. We show that, despite their low sequence identity with metazoan tetraspanins, plant tetraspanins display the typical structural topology and most signature features of tetraspanins in other multicellular organisms. Arabidopsis tetraspanins are expressed in diverse tissue domains or cell types in reproductive tissues, and some accumulate at the highest levels in response to pollination in the transmitting tract and stigma, male and female gametophytes and gametes. Arabidopsis tetraspanins are preferentially targeted to the plasma membrane, and they variously associate with specialized membrane domains, in a polarized fashion, to intercellular contacts or plasmodesmata. A membrane-based yeast (Saccharomyces cerevisiae) two-hybrid system established that tetraspanins can physically interact, forming homo-and heterodimer complexes. These results, together with a likely genetic redundancy, suggest that, similar to their metazoan counterparts, plant tetraspanins might be involved in facilitating intercellular communication, whose functions might be determined by the composition of tetraspanin complexes and their binding partners at the cell surface of specific cell types.

The VASCULATURE COMPLEXITY AND CONNECTIVITY Gene Encodes a Plant-Specific Protein Required for Embryo Provasculature Development

“…Expression levels of VCC and OPS affect both pattern complexity and the connectivity of veins in cotyledons. membrane or to the endoplasmic reticulum when expressed in protoplasts (Boavida et al, 2013). TET3 and a DUF1218-containing protein (AT1G15480) have been found to localize to the plasma membrane and to be enriched in plasmodesmata (Fernandez-Calvino et al, 2011).…”

Functional Analysis of Arabidopsis TETRASPANIN Gene Family in Plant Growth and Development

“…The TET gene family consists of different clades with duplicated or triplicated members (Cnops et al, 2006;Wang et al, 2012;Boavida et al, 2013), showing diverging expression profiles (Figs. 1-3).…”

“…Mutations in animal tetraspanins result in severe defects, such as incurable blindness and impaired fertility (Kaji et al, 2002;Goldberg, 2006). In plants, phylogenetic studies identified 17 tetraspanin genes in the Arabidopsis (Arabidopsis thaliana) genome, most of which are duplicated (Cnops et al, 2006;Wang et al, 2012;Boavida et al, 2013). Mutants of the Arabidopsis TETRASPANIN1/ TORNADO2/EKEKO (TET1/TRN2) show defects in leaf lamina symmetry and venation pattern, root epidermal patterning (Cnops et al, 2000(Cnops et al, , 2006, peripheral zone identity of the SAM (Chiu et al, 2007), and megasporogenesis (Lieber et al, 2011).…”

“…Mutants of the Arabidopsis TETRASPANIN1/ TORNADO2/EKEKO (TET1/TRN2) show defects in leaf lamina symmetry and venation pattern, root epidermal patterning (Cnops et al, 2000(Cnops et al, , 2006, peripheral zone identity of the SAM (Chiu et al, 2007), and megasporogenesis (Lieber et al, 2011). A number of Arabidopsis tetraspanins are expressed in reproductive tissues and at fertilization, and are localized at the plasma membrane of protoplasts (Boavida et al, 2013). However, a systematic analysis of all members of the plant TET gene family in embryonic and vegetative development and upon hormonal and environmental stimuli is lacking.…”

Intercellular communication in Arabidopsis thaliana pollen discovered via AHG3 transcript movement from the vegetative cell to sperm

“…Moreover, the two sperm cell membranes are connected to each other through a tetraspaninenriched microdomain (8). Although all these physical connections presumably ensure that the vegetative nucleus and the sperm cells move in the pollen tube as a unit (known as the "male germ unit"), they also may provide a route for intercellular communication.…”