Gene Families from the Arabidopsis thaliana Pollen Coat Proteome

Abstract

The pollen extracellular matrix contains proteins mediating species specificity and components needed for efficient pollination. We identified all proteins >10 kilodaltons in the Arabidopsis pollen coating and showed that most of the corresponding genes reside in two genomic clusters. One cluster encodes six lipases, whereas the other contains six lipid-binding oleosin genes, including GRP17, a gene that promotes efficient pollination. Individual oleosins exhibit extensive divergence between ecotypes, but the entire cluster remains intact. Analysis of the syntenic region in Brassica oleracea revealed even greater divergence, but a similar clustering of the genes. Such allelic flexibility may promote speciation in plants.

A reference map of the Arabidopsis thaliana mature pollen proteome

“…Furthermore, approximately 4% of the pollen polypeptides are predicted to reside in the nucleus, $5% are presumably associated with the cytoskeleton, $1.6% reside in the vacuole, $0.8% in the cell wall, $0.8% in the ribosome, and the localization of $7% of the proteins cannot currently be predicted. Notably, none of the Arabidopsis pollen coat proteins described in the study of Mayfield et al [17] was identified in our analysis. The extreme hydrophobic properties of these proteins could mean that they were not extracted in our experimental conditions.…”

“…In this study, the authors were able to identify $150 protein spots that varied among different stages of anther development. So far, the only reported proteome analysis in A. thaliana described the constituents of the pollen coat [17]. The work presented here reports the application of proteome analysis techniques to characterize the Arabidopsis mature pollen stage.…”

Signaling Events in Pollen Acceptance or Rejection in the Arabidopsis Species

“…This may involve changes in the lipid properties of the pollen-stigma interface through the actions of lipid-binding oleosin-like proteins or lipases that have been identifi ed in the A. thaliana pollen coat (Mayfi eld et al 2001 ). For example, the pollen glycine-rich protein 17 (GRP17) contains an oleosin domain that has been implicated in this role (Mayfi eld and Preuss 2000 ).…”

“…Interestingly, the exl4 mutant pollen initiated hydration at a similar time to wild-type pollen but then displayed a slower rate of hydration (Updegraff et al 2009 ). Both the grp17 and exl4 mutants displayed mild hydration phenotypes, and it may be that multiple members of the corresponding gene families (Mayfi eld et al 2001 ) need to be knocked out to see a more pronounced hydration defect. Other unknown factors may are also involved in controlling pollen hydration.…”

“…A number of small pollen coat proteins could potentially act as signaling molecules for putative receptors in the stigma papilla (Mayfi eld et al 2001 ;Vanoosthuyse et al 2001 ), and several Brassica candidates for promoting pollen adhesion have been proposed (Doughty et al 1998 ;Luu et al 1997Luu et al , 1999Takayama et al 2000a ). However, there are likely other unknown signaling proteins responsible for activating a cellular response in the stigmatic papilla to promote acceptance of the compatible pollen grain.…”