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BMC Evolutionary Biology

, 10:41

First Online: 12 February 2010Received: 08 May 2009Accepted: 12 February 2010


BackgroundThe availability of genome and transcriptome sequences for a number of species permits the identification and characterization of conserved as well as divergent genes such as lineage-specific genes which have no detectable sequence similarity to genes from other lineages. While genes conserved among taxa provide insight into the core processes among species, lineage-specific genes provide insights into evolutionary processes and biological functions that are likely clade or species specific.

ResultsComparative analyses using the Arabidopsis thaliana genome and sequences from 178 other species within the Plant Kingdom enabled the identification of 24,624 A. thaliana genes 91.7% that were termed Evolutionary Conserved EC as defined by sequence similarity to a database entry as well as two sets of lineage-specific genes within A. thaliana. One of the A. thaliana lineage-specific gene sets share sequence similarity only to sequences from species within the Brassicaceae family and are termed Conserved Brassicaceae-Specific Genes 914, 3.4%, CBSG. The other set of A. thaliana lineage-specific genes, the Arabidopsis Lineage-Specific Genes 1,324, 4.9%, ALSG, lack sequence similarity to any sequence outside A. thaliana. While many CBSGs 76.7% and ALSGs 52.9% are transcribed, the majority of the CBSGs 76.1% and ALSGs 94.4% have no annotated function. Co-expression analysis indicated significant enrichment of the CBSGs and ALSGs in multiple functional categories suggesting their involvement in a wide range of biological functions. Subcellular localization prediction revealed that the CBSGs were significantly enriched in proteins targeted to the secretory pathway 412, 45.1%. Among the 107 putatively secreted CBSGs with known functions, 67 encode a putative pollen coat protein or cysteine-rich protein with sequence similarity to the S-locus cysteine-rich protein that is the pollen determinant controlling allele specific pollen rejection in self-incompatible Brassicaceae species. Overall, the ALSGs and CBSGs were more highly methylated in floral tissue compared to the ECs. Single Nucleotide Polymorphism SNP analysis showed an elevated ratio of non-synonymous to synonymous SNPs within the ALSGs 1.99 and CBSGs 1.65 relative to the EC set 0.92, mainly caused by an elevated number of non-synonymous SNPs, indicating that they are fast-evolving at the protein sequence level.

ConclusionsOur analyses suggest that while a significant fraction of the A. thaliana proteome is conserved within the Plant Kingdom, evolutionarily distinct sets of genes that may function in defining biological processes unique to these lineages have arisen within the Brassicaceae and A. thaliana.

Electronic supplementary materialThe online version of this article doi:10.1186-1471-2148-10-41 contains supplementary material, which is available to authorized users.

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Autor: Haining Lin - Gaurav Moghe - Shu Ouyang - Amy Iezzoni - Shin-Han Shiu - Xun Gu - C Robin Buell


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