Figure 1.

A Requirement of N-Glycosylation Sites in the SRKb Extracellular Domain for the Ability of the Stigma to Inhibit SCRb Pollen.

(A) Schematic structure of the full-length A. lyrata SRKb (top) and its extracellular domain (bottom) showing the location of the four structural subdomains (LLD1, LLD2, EGF-like, and PAN_APPLE) and hypervariable regions (hvI, hvII, and hvIII) that characterize SRK extracellular domains. The positions of the asparagine residues in the N-glycosylation motifs are shown by lollipops.

(B) Microscopic visualization of pollination phenotypes. Representative images are shown for phenotypes observed after pollination with SCRb pollen of stigmas from wild-type untransformed plants lacking SRKb [SRKb(-)] and from transformants expressing wild-type SRKb-FLAG (SRKb) or the mutant SRKb(000000)-FLAG [SRKb(000000)] protein. Note that stigmas expressing wild-type SRKb-FLAG exhibit an intense incompatibility response manifested by the failure of SCRb pollen to germinate and elaborate pollen tubes. By contrast, stigmas expressing the SRKb(000000)-FLAG mutant exhibit a compatible response and allow the growth of numerous SCRb pollen tubes similar to the stigmas of plants lacking SRKb. Bar = 100 μm.

(C) Immunoblot (IB) analysis of SRKb-FLAG proteins from untransformed plants [SRKb(-)] and plants transformed with AtS1pro:SRKb-FLAG [SRKb] and AtS1pro:SRKb(000000)-FLAG [SRKb(000000)]. The upper panel shows immunoblot analysis with anti-FLAG antibody, and the lower panel shows Coomassie blue (CBB) staining as loading control. The asterisk shows a degradation product of SRKb-FLAG.

[See online article for color version of this figure.]