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 materials 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 masses 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.