Hydroxyproline-rich glycoproteins in plant reproductive tissues: structure, functions and regulation

Abstract

The plant reproductive process of pollination involves a series of interactions between the male gametophyte (the pollen grain or pollen tube) and extracellular matrix (ECM) molecules secreted by different cell types along the pollen tube growth pathway in the female organ, the pistil. These interactions are believed to signal and regulate the pollen tube growth process to effect successful delivery of the sperm cells to the ovules where fertilization takes place. Hydroxyproline-rich glycoproteins secreted by plant cells are believed to play a broad range of functions, ranging from providing structural integrity to mediating cell-cell interactions and communication. The pistil and pollen tube ECM is enriched in these highly glycosylated proteins. Our discussions here will focus on a number of these proteins for which most information has been available, from Nicotiana tabacum, its self-incompatible relative N. alata, and Zea mays. In addition, the regulation of the synthesis and glyco-modification of one of these proteins, TTS (transmitting tissue-specific) protein from N. tabacum will be discussed in the light of how differential glycosylation may be used to regulate molecular interactions within the ECM.

The Arabidopsis SOS5 Locus Encodes a Putative Cell Surface Adhesion Protein and Is Required for Normal Cell Expansion

“…SOS5 has high sequence similarity to an endosperm-specific protein from maize ( Figure 6A) and to some pollen surface proteins (data not shown), suggesting a possible role for SOS5 in pollination and/or embryogenesis. Some AGPs also have been shown to play important roles in plant reproduction (Wu et al, 2001).…”

Using Genomic Resources to Guide Research Directions. The Arabinogalactan Protein Gene Family as a Test Case

“…AGPs that have not been published previously (Schultz et al, 2000;Gaspar et al, 2001) are indicated in bold. interpreting DNA microarray results (Wu et al, 2001a). Arabidopsis plants were grown in liquid culture for 8 d. After this time, plants were transferred to low-pH liquid media, either with or without Al.…”

PlusandMinusSexual Agglutinins fromChlamydomonas reinhardtii

“…A second possible agglutination modality, therefore, is that the heads make adhesive contacts with opposite-type shafts. In Solanaceous plants, chimeric HRGPs (the solanaceous lectins) have been shown to recognize sugar residues in chitin Van Damme et al, 2004), and the Cysrich extensin-like proteins expressed in the flowers of Nicotiana tabacum have also been suggested to function as lectins (Wu et al, 2001). By analogy, the agglutinin heads may prove to include surface-localized lectin motifs that recognize distinctive carbohydrate moieties carried by the shafts of the opposite mating type, perhaps displayed in a recognized pattern.…”

“…The plus and minus versions from C. reinhardtii are encoded by different genes and possess complementary adhesive properties, but they also share common features: (1) they are both huge monomeric glycoproteins (native molecular mass > 1000 kD; Adair et al, 1983); (2) their association with the flagellar surface is disrupted by EDTA (Adair et al, 1982), indicating that they are extrinsic membrane proteins; (3) they are both chimeric (Kieliszewski and Lamport, 1994), possessing a large globular head and a fibrous shaft ; (4) they are members of the Hyprich glycoprotein (HRGP) family (Cooper et al, 1983) found as well in the cell walls of most green organisms (reviewed in Cassab, 1998;Serpe and Nothnagel, 1999) and implicated in sexual interactions in higher plants (reviewed in Wu et al, 2001).…”