Lateral or horizontal gene transfer (HGT), the transfer of genetic material between reproductively isolated species, is central to the archaeal and bacterial evolution (Keeling & Palmer, 2008), while the prevalence and importance of this process in the evolution of multicellular organisms remain unclear. Recent evidences indicate that mitochondrial DNAs of land plants are unusually active in HGT relative to plastidial and nuclear genomes (Bock, 2010). Most cases described to date have involved both single and massive transferred gene per species (Mower et al., 2010). Particularly, the HGT example reported in Amborella trichopoda implies acquisition of at least a few dozen and probably hundreds of foreign mitochondrial genes from both vascular and non-vascular plants (Bergthorsson et al., 2004). Cedrus (true cedar) is one of 11 commonly accepted genera in Pinaceae that includes four species localized in two distinct geographical areas around the world: the Himalayan foothills (C. deodara) and the Mediterranean (C. atlantica found in North Africa, C. libani in Turkey, Syria and Lebanon, and C. brevifolia in Cyprus) (Qiao et al., 2007). Here, we report that mitochondria of all four cedar taxa possess an intact introns-interrupting rps3 gene sharing the same genomic context with a downstream overlapping rpl16 gene, as also well documented in some gymnosperm and angiosperm lineages analyzed to date (Regina & Quagliariello, 2010). RT-PCR analysis confirmed that the two genes are cotranscribed as a dicistronic unit that subsequently undergoes post-transcriptional processing. Astonishingly, in Mediterranean cedar species, but not in C. deodara, we found additional rps3 and rpl16 copies, both of these displaying distinctive structural characteristics and high sequence divergence when compared with “native” ones. On the other hand, the near-identity to the hortologous loci of several flowering plants as well as phylogenetic analyses allow us to infer that the extra rps3 and rpl16 sequences detected in C. atlantica, C. libani and C. brevifolia are most likely the result of a HGT event from an angiosperm donor. However, unlike the “native” rps3 and rpl16 genes, the “foreign” copies are only incomplete sequences (or pseudogenes) and, indeed, no corresponding RT-PCR products were obtained. The subcellular location of the rps3 and rpl16 angiosperm-type genes in the Mediterranean Cedrus species, the potential plant donor, the molecular mechanism and implication of this plant-to-plant genetic material exchange within an evolutionary framework will be also discussed. Our study provides new information about the dynamic nature, organization and expression of plant mitochondrial genes, and contributes to assess the magnitude and extent of mitochondrial genetic diversity among the four species of the genus Cedrus of whose we still have limited knowledge.
INFERENCE AND CHARACTERIZATION OF HORIZONTALLY TRANSFER RPS3 AND RPL16 GENES IN CEDRUS SP. MITOCHONDRIA
REGINA, Teresa Maria Rosaria
2012-01-01
Abstract
Lateral or horizontal gene transfer (HGT), the transfer of genetic material between reproductively isolated species, is central to the archaeal and bacterial evolution (Keeling & Palmer, 2008), while the prevalence and importance of this process in the evolution of multicellular organisms remain unclear. Recent evidences indicate that mitochondrial DNAs of land plants are unusually active in HGT relative to plastidial and nuclear genomes (Bock, 2010). Most cases described to date have involved both single and massive transferred gene per species (Mower et al., 2010). Particularly, the HGT example reported in Amborella trichopoda implies acquisition of at least a few dozen and probably hundreds of foreign mitochondrial genes from both vascular and non-vascular plants (Bergthorsson et al., 2004). Cedrus (true cedar) is one of 11 commonly accepted genera in Pinaceae that includes four species localized in two distinct geographical areas around the world: the Himalayan foothills (C. deodara) and the Mediterranean (C. atlantica found in North Africa, C. libani in Turkey, Syria and Lebanon, and C. brevifolia in Cyprus) (Qiao et al., 2007). Here, we report that mitochondria of all four cedar taxa possess an intact introns-interrupting rps3 gene sharing the same genomic context with a downstream overlapping rpl16 gene, as also well documented in some gymnosperm and angiosperm lineages analyzed to date (Regina & Quagliariello, 2010). RT-PCR analysis confirmed that the two genes are cotranscribed as a dicistronic unit that subsequently undergoes post-transcriptional processing. Astonishingly, in Mediterranean cedar species, but not in C. deodara, we found additional rps3 and rpl16 copies, both of these displaying distinctive structural characteristics and high sequence divergence when compared with “native” ones. On the other hand, the near-identity to the hortologous loci of several flowering plants as well as phylogenetic analyses allow us to infer that the extra rps3 and rpl16 sequences detected in C. atlantica, C. libani and C. brevifolia are most likely the result of a HGT event from an angiosperm donor. However, unlike the “native” rps3 and rpl16 genes, the “foreign” copies are only incomplete sequences (or pseudogenes) and, indeed, no corresponding RT-PCR products were obtained. The subcellular location of the rps3 and rpl16 angiosperm-type genes in the Mediterranean Cedrus species, the potential plant donor, the molecular mechanism and implication of this plant-to-plant genetic material exchange within an evolutionary framework will be also discussed. Our study provides new information about the dynamic nature, organization and expression of plant mitochondrial genes, and contributes to assess the magnitude and extent of mitochondrial genetic diversity among the four species of the genus Cedrus of whose we still have limited knowledge.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
