Abstract
Pollen tube guidance, a mechanism to guide pollen tubs to the ovule, is highly species specific and is thought to be one of a mechanism to prevent interspecies crosses. We have recently identified that a group of Defensin-like Cysteine-Rich Polypeptides, LUREs, are the pollen tube attractants secreted from the synergid cells of Torenia fournieri. We further tried to isolate LURE homologues from related species of T. fournieri and compare their sequences and functions for pollen tube guidance. We found one LURE-like protein, named TcCRP1, which is expressed exclusively in the synergid cell of T. concolor, had strong pollen tube attractant activity against T. concolor pollen tubes. TcCRP1 also showed weak attractant activity against T. fournieri pollen tubes. We also found a LURE-like gene that was not expressed in the ovule of T. concolor. Some key amino acids were substituted in its product, suggesting that this gene might be a pseudo-gene. These results suggested that diversification of Cysteine-Rich Polypeptides contribute pollen tube attraction activities. We are currently trying to identify key structure of LUREs for pollen tube attraction.
