An Al-LURE-ing Guidance System

Science Signaling  24 Mar 2009:
Vol. 2, Issue 63, pp. ec104
DOI: 10.1126/scisignal.263ec104

In flowering plants, germinated pollen grains form tubes that must directionally grow through the flower to deliver sperm cells to the egg cell. In the final phase of this journey, pollen tubes must enter the ovule through an opening known as the micropyle and grow toward and into one of the synergid cells located next to the egg cell. Synergid cells are thought to secrete a diffusible signal through a specialized cell wall structure called the filiform apparatus to guide pollen tubes, but the identity of these chemoattractants in several plant species has been elusive. Okuda et al. prepared a complementary DNA library from synergid cells in Torenia fournieri (bluewings or wishbone flower) and identified 16 transcripts that encoded a group of proteins that they named T. fournieri cysteine-rich polypeptides (TfCRPs). Immunofluorescence for TfCRP1 and TfCRP3 was detected only in synergid cells, at the surface of the filiform apparatus closest to the micropyle. T. fournieri pollen tubes grew toward beads that released TfCRP1 or TfCRP3 but not TfCRP2. Pollen tubes from a related species, Lindernia micrantha, did not grow toward the TfCRP1- and TfCRP3-releasing beads, which suggests that these chemoattractants are species specific. The authors renamed TfCRP1 and TfCRP3 LURE1 and LURE2, respectively. T. fournieri ovules that had been injected with antisense morpholino oligonucleotides against LURE1 or LURE2 attracted fewer pollen tubes compared with those injected with control morpholino oligonucleotides. Thus, the LUREs are one set of chemoattractants that guide growing pollen tubes in T. fournieri to their final destination.

S. Okuda, H. Tsutsui, K. Shiina, S. Sprunck, H. Takeuchi, R. Yui, R. D. Kasahara, Y. Hamamura, A. Mizukami, D. Susaki, N. Kawano, T. Sakakibara, S. Namiki, K. Itoh, K. Otsuka, M. Matsuzaki, H. Nozaki, T. Kuroiwa, A. Nakano, M. M. Kanaoka, T. Dresselhaus, N. Sasaki, T. Higashiyama, Defensin-like polypeptide LUREs are pollen tube attractants secreted from synergid cells. Nature 458, 357–361 (2009). [PubMed]