Development and Pollination Regulated Accumulation and Glycosylation of a Stylar Transmitting Tissue-Specific Proline-Rich Protein.

Abstract

The extracellular matrix of stylar transmitting tissues of many angiosperms is enriched in secretory material$ that are believed to be important for interactions with pollen tubes. We have previously characterized two related cDNAs (TTS-1 and TTS-2) for stylar transmitting tissue-specific proline-rich proteins (TTS proteins) from Nicotiana tabacum. We show here that TTS proteins are highly glycosylated proteins with apparent molecular mames ranging between 50 and 100 kD. Results from chemical and enzymatic deglycosylation suggest that TTS proteins have N-linked glycosyl groups, and the extensive glycosylation most probably has resulted from modifications at the proline residues. TTS proteins are localized to the intercellular regions between neighboring transmitting tissue cells, the space in which pollen tubes elongate as they migrate from the stigma toward the ovary. TTS mRNA and protein levels are regulated during pistil development and by pollination. The levels of TTS mRNAs and proteins increase with flower development and reach the maximal levels as flowers approach anthesis. These maximal levels are maintained in the styles for at least 3 to 4 days after pollination, during which time pollen tubes elongate and reach the ovary. Spatially, TTS mRNAs and proteins accumulate first in the stigmatic end of young styles, and their levels progressively increase toward the basal end as pistils mature. Pollination stimulates the levels of TTS mRNAs and proteins in hand-pollinated young styles, which normally accumulate relatively low levels of these TTS gene products. Pollination also qualitatively affects TTS mRNAs and proteins. In pollinated styles, TTS mRNAs are shorter than those in unpollinated styles and underglycosylated TTS protein species begin to accumulate. The elaborate regulatory mechanisms governing TTS mRNAs and proteins during development and by pollination strongly suggest that these proteins may play a functional role in the process of pollination.

Pollination induces mRNA poly(A) tail‐shortening and cell deterioration in flower transmitting tissue

“…When assayed without their poly(A) tails after reannealing with AC44, oligo-dT, and treated with RNase H, the 3' "I-I'S fragments from both the U and L halves of the style were reduced to a discrete band representing the 3' "I-I'S RNA fragments without any poly(A) tails (Figure 2f). Results in Figure 2 We showed previously that pollination induces an increase in the level of TTS mRNAs, and a shortening of their lengths (Wang et aL, 1993; Figure 2g). Using the strategies described above (Figure 2a-d), we showed that "l-rS mRNAs in the pollinated styles had shorter poly(A) tails than those in the unpollinated styles (Figure 2g and h).…”

“…The amounts of two of these mRNA species declined after pollination while the third class of poly(A) tail-shortened mRNAs, TTS (transmitting tissue-specific) mRNAs, was maintained at very high levels for several days after pollination despite extensive transmitting tissue deterioration. I-FS mRNAs are synthesized from two highly homologous genes encoding transmitting tissue extracellular matrixspecific pollen tube growth-promoting and -attracting glycoproteins needed for optimal in vivo pollen tube growth Wang et aL, 1993;Wu et al, 1995). The results presented here suggest that mechanisms exist in the pollinated style to preserve essential mRNAs amidst significant RNA degradative activities within the deteriorating transmitting tissue cells.…”

Arabinogalactan-proteins: structure, expression and function

“…Vol. 58,2001 Multi-author Review Article The GPI anchor has a partial b-galactosyl substitution (*) of its core oligosaccharide and includes a phosphoceramide lipid composed primarily of phytosphingosine and tetracosanoic acid [35]. Potential sites of cleavage by phospholipase C (PLC) and phospholipase D (PLD) are also indicated; cleavage at one or both of these sites would release the AGP from the plasma membrane into the extracellular matrix.…”

“…In contrast, few AGP antibodies are directed against the core protein, which is typically extensively glycosylated. Two notable exceptions are the PAP antibody, which has reactivity directed against a putatively unglycosylated, Lys-rich region of a tomato AGP known as LeAGP-1, and an antibody which has reactivity directed against a bacterially expressed tobacco TTS core protein (table 1) [10,58]. These antibodies have proven useful in localizing the respective expression of an individual AGP core protein (i.e.…”

“…Vol. 58,2001 Multi-author Review Article cleaved in vitro and in vivo to release proteins, including AGPs, from the plasma membrane [33,34]. Thus, the model that emerges is that AGPs containing a GPI anchor are associated with the plasma membrane and are cleaved so as to release the AGP to and beyond the cell wall.…”