Molecular and phylogenetic characterization of the sieve element occlusion gene family in <it>Fabaceae </it>and non-<it>Fabaceae </it>plants

• Main Authors: Müller Boje, Reineke Anna R, Nordzieke Steffen, Jekat Stephan B, Ernst Antonia M, Rüping Boris, Bornberg-Bauer Erich, Prüfer Dirk, Noll Gundula A
• Format: Article
• Language: English
• Published: BMC 2010-10-01
• Series: BMC Plant Biology
• Online Access: http://www.biomedcentral.com/1471-2229/10/219

<p>Abstract</p> <p>Background</p> <p>The phloem of dicotyledonous plants contains specialized P-proteins (phloem proteins) that accumulate during sieve element differentiation and remain parietally associated with the cisternae of the endoplasmic reticulum in mature sieve elements. Wounding causes P-protein filaments to accumulate at the sieve plates and block the translocation of photosynthate. Specialized, spindle-shaped P-proteins known as forisomes that undergo reversible calcium-dependent conformational changes have evolved exclusively in the <it>Fabaceae</it>. Recently, the molecular characterization of three genes encoding forisome components in the model legume <it>Medicago truncatula </it>(<it>MtSEO1</it>, <it>MtSEO2 </it>and <it>MtSEO3</it>; SEO = sieve element occlusion) was reported, but little is known about the molecular characteristics of P-proteins in non-<it>Fabaceae</it>.</p> <p>Results</p> <p>We performed a comprehensive genome-wide comparative analysis by screening the <it>M. truncatula</it>, <it>Glycine max</it>, <it>Arabidopsis thaliana</it>, <it>Vitis vinifera </it>and <it>Solanum phureja </it>genomes, and a <it>Malus domestica </it>EST library for homologs of <it>MtSEO1</it>, <it>MtSEO2 </it>and <it>MtSEO3 </it>and identified numerous novel <it>SEO </it>genes in <it>Fabaceae </it>and even non-<it>Fabaceae </it>plants, which do not possess forisomes. Even in <it>Fabaceae </it>some <it>SEO </it>genes appear to not encode forisome components. All <it>SEO </it>genes have a similar exon-intron structure and are expressed predominantly in the phloem. Phylogenetic analysis revealed the presence of several subgroups with <it>Fabaceae</it>-specific subgroups containing all of the known as well as newly identified forisome component proteins. We constructed Hidden Markov Models that identified three conserved protein domains, which characterize SEO proteins when present in combination. In addition, one common and three subgroup specific protein motifs were found in the amino acid sequences of SEO proteins. <it>SEO </it>genes are organized in genomic clusters and the conserved synteny allowed us to identify several <it>M. truncatula </it>vs <it>G. max </it>orthologs as well as paralogs within the <it>G. max </it>genome.</p> <p>Conclusions</p> <p>The unexpected occurrence of forisome-like genes in non-<it>Fabaceae </it>plants may indicate that these proteins encode species-specific P-proteins, which is backed up by the phloem-specific expression profiles. The conservation of gene structure, the presence of specific motifs and domains and the genomic synteny argue for a common phylogenetic origin of forisomes and other P-proteins.</p>