UniProt release 2012_05
Published May 16, 2012
Headline
Sex by deception
All is fair in love and war and… species survival, including the most brazen cheating. In this context, strategies developed by orchids of the genus Ophrys to attract pollinators are astounding. While the majority of flowering plants achieve pollination by exploiting the food-seeking behavior of animals, Ophrys uses alternative ploys that exploit their mate-seeking behavior. These beautiful flowers imitate female insects to attract males, predominantly male hymenoptera. They mimic the insect body through one modified petal, called the labellum, but the misleading cues are not only visual and tactile: they are also chemical. During development the Ophrys labellum accumulates substances that mimic sex pheromones – which consist mostly of cuticular hydrocarbons, such as alkanes and alkenes – that induce the pollinator to attempt mating (pseudocopulation) with the labellum. During pseudocopulation, pollen becomes attached to the hapless suitor, which transfers this pollen to other flowers when it is once again enticed into pseudocopulation.
This pollination system is highly specialized, with each orchid species targeting a single pollinator with chemical cues consisting of alkenes whose specificity is determined by the precise position of the double bonds. This allows even closely related Ophrys species, living in the same environment and in the absence of geographic barriers, to remain reproductively separated, since they attract different insects. The enzymes involved in Ophrys alkene synthesis have been recently identified. The SAD2 desaturase has the catalytic activity and tissue-specific expression pattern (i.e preferentially in the labellum) expected for a determinant of pollination specificity. Small differences in the expression level or sequence of SAD2 homologs could explain the observed differences in desaturation among Ophrys species, and hence the selective attraction of specific pollinators. Although alignments of orthologous SAD2 sequences from Ophrys sphegodes and O. exaltata indicate striking identity, as yet uncharacterized variations could conceivably affect the precise reaction products.
As of this release, SAD2 gene products have been manually annotated in UniProtKB. They can be retrieved by searching the Swiss-Prot section for SAD2 in ‘Gene names’ (gene:SAD2 AND reviewed:yes). Both available sequences (from O. sphegodes and O. exaltata) can be selected and aligned directly from the search output.
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Update to Reference proteomes in UniProtKB
With the significant increase in the number of complete genomes sequenced, it is critically important to organize this data in a way that allows users to effectively navigate the growing number of available complete proteome sequences. In collaboration with Ensembl and the NCBI Reference Sequence collection, UniProt began this organization by defining a set of ‘reference proteomes’. These were first introduced in UniProt release 2011_09 and the keyword ‘Reference proteome’ was created to allow their easy retrieval.
The number of reference proteomes has grown from 455 in UniProt release 2011_09 to 549 in release 2012_05. The proteomes have been selected to provide broad coverage of the tree of life, and constitute a representative cross-section of the taxonomic diversity to be found within UniProtKB.
The reference proteome will be continuously reviewed as new proteomes of interest become available and as existing taxonomic classifications are revised. We would very much welcome feedback on our current list of reference proteomes and suggestions for new candidates via help@uniprot.org.