Biology Reference
In-Depth Information
In the A. thaliana female sterile feronia and sirene mutants, wild type pollen
tubes enter the mutant ovules but fail to cease growth or burst. In addition to
this defect, multiple pollen tubes gain access to feronia and sirene mutant ovules
[3,35]. Based on these results, it was suggested that repulsion of supernumerary
tubes does not initiate until pollen tube reception occurs. Our observations with
wild type pollen tubes in this in vitro assay indicate this is not the case - repul-
sion responses occurred well before tube growth terminated or tubes released their
cytoplasm (n = 50, Fig. 3j, 3n). Moreover, while previous work suggested that
female gametophyte cells release an inhibitory signal [3,35], our results show that
repulsion initiated soon after the pollen tubes entered the micropyle and long
before they reached the female gametophyte (Fig. 3). Thus, this work points to a
diffusible repulsive signal that is sufficient to override the ovule attractant. This
signal may be derived directly from the diploid cells that surround the micropyle,
from the female gametophyte, or from the successfully targeted, but unlysed, pol-
len tubes.
Conclusion
Based on the results described here, we have defined three signaling events that
regulate pollen tube guidance in A. thaliana: i) contact-mediated competence
conferred by the stigma and style, ii) diffusible ovule-derived attractants and iii)
repellents exuded from recently-targeted ovules. The species specificity and diffu-
sion properties of the ovule attractant are consistent with a protein signal, while
the abrupt transmission and response to the repellent suggests the activity of a
small molecule, a peptide, or post-translational modifications to signals present
before fertilization. This investigation also provides a platform to confirm the
roles of candidate guidance molecules and to explore the phenotypes of A. thali-
ana mutants, including those that affect the development of diploid [9,10] and
haploid [3,16,35] female tissues or pollen tubes [36]. The ability to characterize
interspecies pollination interactions with this assay could lead to improvements
in generating novel plant hybrids, a process that often requires in vitro manipula-
tions [37].
Methods
Plant Growth and Material
Pollen was derived from LAT52:GFP transgenic lines (Columbia background).
Stigmas, styles, and ovules were from the A. thaliana male sterile mutant, ms1
(CS75, Landsberg background) or from A. arenosa (CS3901), O. pumila
